behavior

JoVE行動学は、人間や動物の行動を理解するための観察および実験手法を公開しています。このセクションには、内外の刺激に対する遺伝的原因と生理学的反応を分析する方法と、関係する脳領域を調べる方法が含まれています。

行動学

biochemistry

JoVE生化学は、生体分子（タンパク質、核酸、炭水化物、脂質、代謝物など）の構造と機能、および生物学的プロセス中に起こるそれらの相互作用と変換についての理解を深める方法を出版しています。

生化学

bioengineering

JoVE生物工学は、物理学と生命科学を融合して基本的な生物学的プロセスと機能を理解する方法と技術を出版しています。このセクションでは、病気の測定、診断、治療を改善するための物理科学的ツールとアプローチについても特集します。

生物工学

biology

JoVE生物学は、細胞生物学、分子生物学、生命体生物学の分野で使用される方法を出版しています。これは、標準的な技法の新しいアプリケーションから、生物の基本的な生物学的機能を理解することを目的とした新規のアプローチにまで及びます。

生物学

cancer research

JoVEがん研究は、がん生物学の研究で使用される技術を出版しています。このセクションでは、発がん、薬剤耐性のメカニズム、診断、転移、革新的な治療法に取り組む研究方法論を取り上げます。

がん研究

chemistry

JoVE化学は、分析化学、有機化学、高分子化学、物理化学、無機化学など、幅広い分野の方法を出版しています。このセクションには、高度なまたはユニークなアプリケーション向けの材料および低分子の設計・調整も含まれています。

化学

developmental biology

JoVE発生生物学では、分子、細胞、組織、器官、および生物全体のレベルにおける、試験管内および/または生体内での生物発生を研究するのに使用される方法と技術を出版しています。

発生生物学

engineering

JoVE工学では、工学と応用物理学で利用される方法と技術を出版しています。方法には、機械、電気、化学のエンジニア、物理学者、材料科学者からの寄稿が含まれます。

工学

environment

JoVE環境学は、地球のプロセスと生態系を研究し、環境問題に対処するための研究方法と技術を出版しています。このセクションでは、農業および食品科学だけでなく、幅広い学際的な環境研究分野からの実験室およびフィールドベースの方法を取り上げます。

環境学

genetics

JoVE遺伝学は、ゲノミクス、遺伝子発現、遺伝子工学、後生遺伝学など、遺伝学のすべての分野（すべての生物）に取り組む方法を出版しています。このセクションでは、塩基配列決定技術とその応用の進歩についても特に取り上げます。

遺伝学

immunology and infection

JoVE免疫学と感染では、病原体に対する生物学的反応、感染に対する免疫反応、基本的な微生物学、および感染性微生物に対する新しい治療法を評価するための方法と技術を出版しています。

免疫・感染学

medicine

JoVE医学では、生物医学研究方法と臨床応用を出版しています。このセクションでは、疾患の動物モデル、医療処置、手術、患者のケーススタディ、および臨床試験の方法論について説明します。

医学

neuroscience

JoVE神経科学では、脳と神経系の構造、機能、生理学、および病態生理学を研究するための方法を出版しています。このセクションには、神経疾患および神経障害の潜在的な治療基盤と外科技術も含まれています。

神経科学

jove journal

JoVE Journal

科学ビデオジャーナル。査読された論文。学際的。

https://cloudfront.jove.com/files/banners/journal/journal_lander.jpg

Research

2D NMR: Heteronuclear Single-Quantum Correlation Spectroscopy (HSQC)

Heteronuclear single-quantum correlation spectroscopy (HSQC) is a 2D NMR technique that reveals one-bond correlations between hydrogen and a heteronucleus. The HSQC experiment is similar to the heteronuclear correlation experiment (HETCOR) but is more sensitive. In the HSQC spectrum, the proton chemical shift is plotted on the horizontal F2 axis, while the 13C chemical shift is plotted on the vertical F1 axis. The corresponding proton and 13C spectra are also shown. The HSQC contour plot does not have any diagonal peaks. All the cross-peaks indicate the protons directly attached to each carbon in a molecule. Similar to the COSY spectrum, imaginary lines are drawn in horizontal and vertical directions to identify the correlated peaks.
For example, the HSQC spectrum of 2-chlorobutane has a carbon signal at 11 ppm that can be assigned to the shielded methyl group and correlated to the proton multiplet at 1.01 ppm. The carbon signal at 24.8 ppm arises from the deshielded methyl group, which correlates to the proton multiplet at 1.52 ppm. Similarly, the methylene carbon signal at 33.3 ppm and methine carbon signal at 60.4 ppm correlate to the multiplets at 1.72 and 3.96 ppm, respectively.&#160; HSQC is a very useful technique for structurally elucidating complex molecules and is routinely used in protein NMR studies.

Heteronuclear single-quantum correlation spectroscopy (HSQC) is a 2D NMR technique that reveals one-bond correlations between hydrogen and a ...

2D NMR: Overview of Heteronuclear Correlation Techniques

Heteronuclear correlation spectroscopy is an analytical technique that investigates the coupling between different types of nuclei, often a proton and an X-nucleus, such as carbon-13 or nitrogen-15. This method is commonly used in nuclear magnetic resonance (NMR) spectroscopy to gain insights into complex chemical compounds&#39; structural and compositional aspects. A typical heteronuclear correlation spectrum displays X-nucleus chemical shifts on one axis and a proton spectrum on the other axis. Cross-peaks reveal the connection between specific protons and X-nuclei.
The main heteronuclear correlation experiments include HETCOR, HSQC, HMQC, and HMBC. HSQC, HMQC, and HMBC record the proton spectrum, whereas the X-nucleus spectrum is recorded by standard heteronuclear correlation spectroscopy or HETCOR. The HETCOR-HMQC-HSQC group of experiments cannot detect X-nuclei without an attached proton. HETCOR is used when ultrahigh peak resolution is required along the X-nucleus axis.
The heteronuclear single quantum correlation technique, or HSQC, investigates proton-to-X-nucleus single bond correlations. In an HSQC experiment, polarization is transferred from a proton nucleus to a neighboring X-nucleus and then back to the proton nucleus. The signal from the proton nuclei is then recorded. HSQC generates a spectrum like that of heteronuclear multiple-quantum correlation spectroscopy or HMQC but uses a different suppression method, providing better X-nucleus resolution along the axis.
Heteronuclear multiple-bond correlation, or HMBC, is a proton-detected experiment, like HMQC but with a longer initial delay time. This experiment is used to observe long-range proton to X-nucleus connectivity separated by 2-3 bonds, with some experiments going out to 4 or 5 bonds. In an HMBC experiment, direct one-bond correlations are suppressed as part of the sequence. The spectra of HMBC give rise to cross peaks that correlate which protons are coupled to what other specific X-nucleus is more than one bond away. The gradient HMBC (gHMBC) pulse sequence offers better suppression of interfering signals, making it particularly useful for analyzing complex molecules with overlapping signals.

Heteronuclear correlation spectroscopy is an analytical technique that investigates the coupling between different types of nuclei, often a proton and an ...

2D NMR: Homonuclear Correlation Spectroscopy (COSY)

Homonuclear correlation spectroscopy, or COSY, is a 2-dimensional NMR technique that provides information about coupled protons. Typically, the geminal and vicinal coupling are observed. For example, consider the COSY spectrum of ethyl acetate, where its 1D proton NMR spectrum is plotted along the vertical and horizontal axes with their corresponding chemical shift scale. Three spots on the diagonal corresponding to the three peaks in the 1D proton spectrum are called diagonal peaks. The COSY spectrum is symmetric about the diagonal, with signals above and below the diagonal called cross-peaks or off-diagonal peaks. An imaginary line is drawn from diagonal peaks parallel to the horizontal axis, leading to a cross peak. A vertical line is then drawn from the same cross peak towards the diagonal peak to correlate the peaks. The off-diagonal peaks correlating the multiplets at 1.25 and 4.2 ppm indicate that the methyl protons are coupled to the methylene protons. The signal at 2 ppm is not associated with cross-peaks because the protons are not involved in homonuclear coupling. A COSY spectrum is useful when overlapping multiplets complicate the corresponding 1D spectrum.

Homonuclear correlation spectroscopy, or COSY, is a 2-dimensional NMR technique that provides information about coupled protons. Typically, the geminal ...

Insensitive Nuclei Enhanced by Polarization Transfer (INEPT)

Insensitive Nuclei Enhanced by Polarization Transfer (INEPT) is an advanced Nuclear Magnetic Resonance (NMR) technique specifically designed to detect and enhance the signals of low-abundance nuclei, such as carbon-13 and nitrogen-15, in small molecules. The fundamental principle behind INEPT is the transfer of polarization from a more abundant and highly polarizable nucleus, typically hydrogen-1, to the low-abundance nucleus of interest. This process effectively boosts the NMR signal of the low-abundance nuclei, making them more easily detectable.
The INEPT technique involves a series of carefully timed radiofrequency (RF) pulses applied to the sample. These RF pulses excite the more abundant nuclei, causing them to align their spins in a specific manner. Through the process of spin coupling, the polarization of the more abundant nuclei is then transferred to the low-abundance nuclei. As a result, the NMR signal of these low-abundance nuclei is significantly enhanced, allowing for a more detailed analysis of the molecular structure.
Various pulse sequences have been developed to improve the observability of these low-abundance nuclei when coupled to a high-receptivity nucleus. The INEPT pulse sequence combines a spin echo and selective population inversion, which includes 90&#176; and 180&#176; pulses on the high-sensitivity (the I spins) and low-sensitivity nuclei (the S spins), respectively. Coupling-constant-based delays between pulses facilitate magnetization transfer through space or bond interactions. Additional RF pulses and delays invert the low-gamma magnetization, producing an observable NMR signal. The net result is an enhanced NMR signal from low-gamma nuclei that would otherwise be challenging to detect.
Various pulse sequences have been developed to improve the detection of low-abundance nuclei when coupled with high-receptivity nuclei such as protons. The INEPT sequence yields enhanced signals for insensitive nuclei, with half of the CH group producing negative peaks and the other half positive peaks. This pattern allows for discrimination between different types of carbon-hydrogen bonds within the molecule.
Decoupling methods can be employed to enhance sensitivity and resolution in distinguishing various carbon-hydrogen bonds, making INEPT an invaluable tool in the chemical and pharmaceutical industries.

Insensitive Nuclei Enhanced by Polarization Transfer (INEPT) is an advanced Nuclear Magnetic Resonance (NMR) technique specifically designed to detect and ...

Two-Dimensional (2D) NMR: Overview

The 1D NMR spectrum of large and complex molecules like natural products has complicated splitting patterns and overlapping signals, which can be easily interpreted using 2-dimensional (2D) NMR. Unlike 1D NMR, 2D NMR has two frequency axes that provide the coupling information between the nucleus A and nucleus B in a molecule. The process from which 2D spectra are obtained has four steps.
The first step is the preparation period, during which nucleus A is excited with a radiofrequency pulse. The second step is the evolution or wait period t1, which is incremented systematically, and no data is observed during this period. The next step is the mixing period, in which a second radiofrequency pulse is introduced, which transfers the magnetization to the spins of nucleus B. In the last step, the magnetization of nuclear spins from B is detected during the acquisition time t2 for each t1. Time domains t1 and t2 are Fourier transformed into frequency domains f1 and f2, and these correspond to two dimensions of 2D spectra, while the third dimension is the intensity. In 2D experiments, coupling between the same kind of nucleus is called homonuclear 2D experiments, whereas coupling between two types of nucleus is called heteronuclear 2D experiments. 2D spectra can be displayed as stacked or contour plots. When presented as stacked plots, 2D spectra are difficult to interpret. The contour plot is the horizontal cross-section of a stacked plot where the size of the circles shows the signal intensity. Its interpretation is straightforward and it is preferred for data analysis.

The 1D NMR spectrum of large and complex molecules like natural products has complicated splitting patterns and overlapping signals, which can be easily ...

2D NMR: Overview of Homonuclear Correlation Techniques

Homonuclear correlation spectroscopy (COSY) is a powerful technique used in Nuclear Magnetic Resonance (NMR) spectroscopy to study the correlations between nuclei of the same type within a molecule. It provides information about scalar couplings between adjacent nuclei, which helps determine connectivity and structural information. There are several COSY variants, each with its unique strengths and experimental parameters.
COSY90 is the standard two-dimensional (2D) COSY experiment that utilizes a second 90-degree pulse to achieve high sensitivity and resolution. It excels in analyzing small to medium-sized molecules and provides information on directly coupled protons. COSY45, similar to COSY90, uses 45-degree pulses instead of 90-degree pulses. This results in reduced sensitivity but improved resolution.
Long-range COSY (LR-COSY) extends the COSY experiment to detect scalar couplings between nuclei further apart in the molecule. It achieves this by combining multiple pulse sequences and magnetization transfers.
Relayed COSY is a variant of COSY that adds extra pulses to the standard pulse sequence to produce cross-peaks between cross-peaks, showing specific molecular connections hidden by overlapping signals.
TOCSY (Total Correlation Spectroscopy), also known as HOHAHA (Homonuclear Hartmann-Hahn Spectroscopy), reveals all through-bond connectivity between all coupled nuclei. TOCSY is especially useful for analyzing molecules with overlapping signals and complex coupling patterns.
NOESY (Nuclear Overhauser Effect Spectroscopy) measures the nuclear overhauser effect, which arises from dipole-dipole interactions between nuclei. It provides information about spatial proximity and can be used to determine the three-dimensional structure of a molecule.
ROESY (Rotating-frame Overhauser Enhancement Spectroscopy) is similar to NOESY but employs a different mechanism to obtain through-space correlations. It provides information about spatial proximity and is particularly useful for studying molecules with weak NOE signals.
In conclusion, choosing a COSY variant depends on the molecule or reaction under investigation and the desired information. The right COSY variant can be determined based on molecular size, coupling complexity, and the need for spatial or long-range connectivity data.

Homonuclear correlation spectroscopy (COSY) is a powerful technique used in Nuclear Magnetic Resonance (NMR) spectroscopy to study the correlations ...

Double Resonance Techniques: Overview

Double resonance techniques in Nuclear Magnetic Resonance (NMR) spectroscopy involve the simultaneous application of two different frequencies or radiofrequency pulses to manipulate and observe two distinct nuclear spins. One important application of double resonance is spin decoupling, which selectively suppresses coupling with one type of nucleus while observing the NMR signal from another nucleus, simplifying the spectrum and enhancing resolution.
Spin decoupling is usually achieved by irradiating the sample atoms with a suitable radio frequency (rf) pulse sequence, effectively eliminating all the coupling with one nuclide. This simplifies the observed spectrum, making it easier to analyze and understand the relationships between different nuclei.
Double resonance experiments can be classified as heteronuclear or homonuclear, depending on whether the two sets of nuclei are of different isotopes or the same isotope, respectively. They can also be selective or nonselective, depending on whether the irradiating frequency covers only a portion or all of the resonance frequencies.
In nonselective heteronuclear decoupling, samples are exposed to an appropriate radiofrequency range to remove all coupling with one nuclide. However, increased external field strengths necessitate more powerful irradiation across broader frequency ranges. In certain instruments, continuous irradiation creates enough heat to cause damage to thermally sensitive samples.
To overcome these problems, modern methods using a series of pulses and exact timing delays, like J-modulated spin echo pulse sequences, can be employed to eliminate or adjust coupling effects within the spectrum.
For example, the attached proton transfer (APT) experiment applies a J-modulated spin echo pulse sequence to focus on the phase of detected carbon signals. Carbon atoms attached to an even number of protons exhibit positive signals in the spectrum, while those bonded to an odd number of protons appear as negative signals.
It utilizes a combination of a 180&#176; proton pulse and broadband decoupling to simplify spectral interpretation and assign multiplicities. The 180&#176; pulse is applied to the protons during the APT experiment. Its role is to refocus the spin coupling evolution that naturally occurs due to interactions between protons and carbons.
Specifically, after the 90&#176; pulse creates transverse magnetization, the 180&#176; pulse ensures that the effects of coupling are frozen during the initial period where the decoupler is turned off. This means the chemical shifts evolve only during the time 1/J&#8203; (the coupling constant period) after the first 180&#176; pulse.
By carefully timing this pulse sequence, the experiment isolates carbon multiplicities by utilizing the J-coupling between carbons and their attached protons. After the coupling evolution period (1/J&#8203;), broadband decoupling is turned on. This removes the J-coupling signals, collapsing multiplets into single peaks for each carbon resonance.
The decoupling ensures that carbon signals are free of splitting, allowing for a clear differentiation of signals based on phase (positive or negative) rather than splitting patterns.
The APT technique selectively enhances carbon signals, providing valuable information about carbon-proton connectivity, the number of attached hydrogen atoms, and the overall molecular structure.

Double resonance techniques in Nuclear Magnetic Resonance (NMR) spectroscopy involve the simultaneous application of two different frequencies or ...

&sup1;H NMR of Labile Protons:  Deuterium (&sup2;H) Substitution

This lesson illustrates the role of deuterium substitution in simplifying the NMR spectrum of compounds comprising labile protons. One method employed is the use of deuterium. Amongst the three isotopes of hydrogen, deuterium (2H) has a nucleus composed of one proton and one neutron. When the D2O solvent is added to a pure dry ethanol solution, its labile proton is substituted with deuterium.
<img alt="Figure1" src="/files/ftp_upload/12280/12280-PT_Figure_1.svg" style="text-align: center; height: 700px;" />
Figure 1. The comparison of the proton NMR spectra of pure dry ethanol and the same in D2O solvent.
The signals from deuterium are not observed in a proton NMR spectrum, as deuterium&#8211;proton coupling is negligible, and no spin-spin splitting occurs between them. As shown in Figure 1, the NMR spectra of pure ethanol and ethanol in deuterium, the disappearance of the triplet in the latter, confirms that it corresponds to the labile &#8211;OH proton. Furthermore, the methylene protons that initially showed up as a multiplet transform to a quartet, proving that the multiplet is due to the coupling with the &#8211;OH proton and the methyl protons.

This lesson illustrates the role of deuterium substitution in simplifying the NMR spectrum of compounds comprising labile protons. One method employed is ...

Nuclear Overhauser Enhancement (NOE)

Irradiation of a spin-active nucleus causes an increase or decrease in the signal intensity of neighboring nuclei that are not necessarily chemically bonded or involved in J-coupling. &#160;This phenomenon, called the Nuclear Overhauser Enhancement (NOE), results from through-space interactions between the nuclear spins. The NOE effect decreases with increasing internuclear distance and is generally not observed beyond 4 angstroms. In NOE, dipole-dipole interactions between neighboring spin-active nuclei result in the transfer of nuclear spin polarization. These interactions can cause an increase or decrease in the signal intensity, which results in a positive or negative NOE, respectively.
NOE can be applied to improve the signal intensity of less sensitive nuclei such as carbon-13. Proton-decoupled carbon-13 spectra show a positive NOE effect, where the carbon signal intensities are substantially increased compared to those in proton-coupled spectra.
Targeted irradiation of specific nuclei can also reveal through-space proximity, which helps confirm stereochemistry and verify spectral peak assignments. The NOE effect is also applied in 2D NMR experiments, such as Nuclear Overhauser Effect Spectroscopy (NOESY), to determine the 3D structure of proteins.

Irradiation of a spin-active nucleus causes an increase or decrease in the signal intensity of neighboring nuclei that are not necessarily chemically ...

&sup1;H NMR of Labile Protons: Temporal Resolution

Protons bonded to heteroatoms such as nitrogen and oxygen exhibit a range of chemical shift values. This is due to the varying degree of hydrogen bonding between the proton and the heteroatom in other molecules. The extent of hydrogen bonding affects the electron density around the proton, thereby giving different chemical shift values for the protons in the proton NMR spectrum.
The &#8211;OH proton in alcohols typically appears in the range of &#948; 2 to 5 ppm but can vary depending on the specific alcohol and conditions. This &#8211;OH proton undergoes rapid proton exchange with other molecules and is referred to as a labile proton. So, the exact &#948; value of the &#8211;OH proton and the spin-spin coupling involving the &#8211;OH proton and the other protons in the alcohol depends on the rate of the &#8211;OH proton exchange. The proton exchange rate, in turn, depends on multiple factors, including the purity of the alcohol sample, temperature, and solvent.
<img alt="Figure1" src="/files/ftp_upload/12279/12279-PT_Figure_1.svg" style="text-align: center; height: 350px;" />
Figure 1. The triplet of a &#8211;OH proton in the proton NMR spectrum of neat ethanol.
For example, the &#8211;OH proton exchange in a pure dry ethanol sample is very slow on the NMR time scale, giving enough time for the spin-spin coupling. Consequently, as depicted in Figure 1, the proton NMR spectrum of pure dry ethanol shows a triplet for the &#8211;OH proton due to the spin-spin coupling with adjacent methylene protons. The methylene protons are seen as a multiplet due to the coupling with the &#8211;OH proton and the methyl protons.
The presence of trace amounts of an acid or base increases the proton exchange rate. The proton exchange becomes rapid, and the NMR spectrometer only records an average of all the possible environments for the &#8211;OH proton.
<img alt="Figure2" src="/files/ftp_upload/12279/12279-PT_Figure_2.svg" style="text-align: center; height: 325px;" />
Figure 2. The broad singlet of a &#8211;OH proton in the proton NMR spectrum of neat ethanol.
As a result, as recorded in Figure 2, the &#8211;OH proton exhibits a broad singlet. The protons from the adjacent methylene group present a quartet where the splitting is caused only by the adjoining methyl group.

Protons bonded to heteroatoms such as nitrogen and oxygen exhibit a range of chemical shift values. This is due to the varying degree of hydrogen bonding ...

&sup1;H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR

The axial and equatorial protons in cyclohexane can be distinguished by performing a variable-temperature NMR experiment. In this process, except for one proton, the remaining eleven protons are replaced by deuterium. The deuterium substitution avoids the possible peak splitting caused by the spin-spin coupling between the adjacent protons. The remaining proton flips between the axial and equatorial positions.
<img alt="Figure1" src="/files/ftp_upload/13016/13016-PT_Figure_1.svg" style="text-align: center; height: 480px;" />
Figure 1. The temperature-dependent proton NMR spectra of cyclohexane.
Figure 1 depicts the proton NMR spectrum of the deuterium substituted sample, recorded at various temperatures. At room temperature, the rapid ring flipping of cyclohexane results in a single sharp peak. As the temperature is lowered to &#8722;60&#176;C, the rate of chair-chair interconversion reduces, resulting in the broadening of the peak.
Further lowering of the temperature broadens the peak, forming a saddle that splits into two peaks. On reaching a temperature lower than &#8722;89&#176;C, two sharp, well-resolved peaks corresponding to the equatorial and axial protons are formed. The peaks corresponding to the equatorial and axial protons occur at &#948; 1.62 and 1.14, respectively. At such low temperatures, the rate of chair-chair interconversion is reduced significantly, enabling the detection of the two distinct sets of protons on the NMR time scale.

The axial and equatorial protons in cyclohexane can be distinguished by performing a variable-temperature NMR experiment. In this process, except for one ...

&sup1;H NMR of Conformationally Flexible Molecules: Temporal Resolution

At room temperature, the chair conformer of cyclohexane undergoes rapid ring flipping between two equivalent chair conformers at a rate of approximately 105 times per second. These two chair conformers are in equilibrium. The rapid ring flipping results in the interconversion of the axial proton to an equatorial proton and an equatorial to the axial proton. Such interconversions are too rapid and cannot be detected on the NMR timescale. Hence, the NMR spectrometer cannot distinguish between the axial and equatorial protons, resulting in a single peak at &#948; 1.4.
Similarly, NMR averages all the conformations of any molecule with rapid conformational equilibria. For example, the CH3 protons in bromoethane have a single resonance and coupling constant for splitting by the CH2 protons due to the rapid internal rotation of the carbon-carbon bond. Lastly, besides conformational equilibria, the time-averaging effect of NMR spectroscopy is also observed in some chemical reactions.

At room temperature, the chair conformer of cyclohexane undergoes rapid ring flipping between two equivalent chair conformers at a rate of approximately ...

Mass Spectrometry: Carboxylic Acid, Ester, and Amide Fragmentation

The fragmentation patterns observed for compounds such as carboxylic acids, esters, and amides in the mass spectra include &#9082;-cleavage and McLafferty rearrangement. Fragmentation by &#9082;-cleavage preferentially occurs at the carbon-carbon bond at the &#9082;-position next to the carboxylic group to generate a neutral radical and a cation. Long chain compounds with hydrogen at their &#947;-carbon undergo McLafferty rearrangement to give a radical cation and a neutral alkene.
For example, the fragmentation of butyramide is demonstrated in Figure 1. The molecular ion peak of butyramide, which contains one nitrogen atom, shows an odd mass-to-charge ratio of 87. Fragmentation of butyramide molecular ion by &#9082;-cleavage produces a cation at a mass-to-charge ratio 44. In addition to &#9082;-cleavage, butyramide molecular ion also undergoes fragmentation via McLafferty rearrangement. The base peak at the mass-to-charge ratio 59 arises due to McLafferty rearrangement.
<img alt="Figure1" src="/files/ftp_upload/13051/13051_PT_Figure_1.svg" style="text-align: center; height: 250px;" />

The fragmentation patterns observed for compounds such as carboxylic acids, esters, and amides in the mass spectra include &#9082;-cleavage and McLafferty ...

Chemical Ionization (CI) Mass Spectrometry

The molecular ion peak of a molecule in the mass spectrum provides vital information for molecular identification. However, conventional electron impact ionization can lead to the rapid dissociation of some molecular ions before they reach the detector. A milder ionization method is required to increase the lifetime of such ionized analyte molecules. Chemical ionization (CI) is a gas-phase protonation reaction useful for mass-analyzing analyte molecules that are easily protonated to yield the corresponding conjugate acid. In this process, the sample is mixed with an excess reagent gas, which ensures the electron impact occurs primarily on the reagent gas. The charged species formed from the reagent protonates the analyte molecule, producing a relatively stable protonated analyte (conjugate acid) compared to the molecular ion. This results in an M+1 peak in the mass spectrum. The conjugate acid may then undergo fragmentation that generates additional signals.
For example, the CI of di-sec-butyl ether in methane gas illustrates this process. When the ether is mixed with excess methane gas as a reagent, electron impact occurs on methane rather than the ether. The resulting methane radical cation can react with another methane molecule to generate a methane radical and a methanium ion. The methanium ion is a source of gas-phase protons, which can protonate the ether to form its conjugate acid. The sequential reactions during the chemical ionization of di-sec-butyl ether are depicted in Figure 1.
<img alt="Figure1" src="/files/ftp_upload/12300/12300_PT_Figure_1.svg" style="text-align: center; height: 175px;" />
Figure 1: Chemical ionization of di-sec-butyl ether methane mixture.
This conjugate acid of the ether (m/z = 131) is relatively more stable than the molecular ion (m/z = 130) of ether formed via the conventional electron impact ionization. In the traditional route, the molecular ion undergoes fragmentation via &#945; cleavage, giving a signal at m/z = 101. Figure 2 illustrates the reactions that occur during electron impact ionization directly on di-sec-butyl ether.
<img alt="Figure2" src="/files/ftp_upload/12300/12300_PT_Figure_2.svg" style="text-align: center; height: 175px;" />
Figure 2: Electron impact ionization of di-sec-butyl ether and fragmentation of the molecular ion.
So, the mass spectra of di-sec-butyl ether ionized via CI feature an M+1 peak at m/z = 131. On the other hand, mass spectra of di-sec-butyl ether ionized via electron impact ionization do not show any peak at the m/z value of its molecular weight. Figures 3a and 3b show the mass spectra of di-sec-butyl ether ionized via the electron impact and chemical ionization methods, respectively.
<img alt="Figure3" src="/files/ftp_upload/12300/12300_PT_Figure_3.svg" style="text-align: center; height: 225px;" />
Figure 3:&#160;a) No m/z = 130 peak is visible in the mass spectrum obtained via electron impact ionization of di-sec-butyl ether. b) The m/z = 131 peak is clearly visible in the mass spectrum obtained via chemical ionization of di-sec-butyl ether.

The molecular ion peak of a molecule in the mass spectrum provides vital information for molecular identification. However, conventional electron impact ...

Mass Spectrometry: Alkyl Halide Fragmentation

Chlorine isotopes exist as 35Cl and 37Cl in a 3:1 ratio, while bromine isotopes exist as 79Br and 81Br in a 1:1 ratio. The mass spectrum of alkyl halides typically produces two distinct molecular ion peaks, the molecular ion peak, [M], and the molecular ion plus two, [M + 2] peak. The relative heights of these two peaks are proportional to the isotopic abundance ratios of the halide. For example, 2&#8208;chloropropane and 1&#8208;bromopropane display two peaks with relative peak heights in a 3:1 and 1:1 ratio, respectively.
Alkyl halides typically lose a non-bonding electron from the halogen to form molecular ions. The base peak results from the heterolytic cleavage of the carbon&#8211;halogen bond, where the bonding electrons go to the most electronegative atom, forming a cation and halogen atom. Interestingly, the &#9082;-cleavage is observed only in alkyl chlorides, not alkyl bromides. In alkyl chlorides, the&#160; C&#8211;Cl and C&#8211;C bonds exhibit similar strengths, while in alkyl bromides, the C&#8211;Br bond is weaker than the C&#8211;C bond. Consequently, the alkyl chlorides form a stable cation, where the positive charge is shared between the two atoms.
While less commonly discussed, fluoroalkanes and iodoalkanes exhibit unique fragmentation behavior. Fluoroalkanes, due to the strength of the C&#8211;F bond and the presence of only one isotope (19F), show limited fragmentation and lack isotopic peaks. Iodoalkanes, with their weak C&#8211;I bond and a single isotope (127I), predominantly fragment by losing iodine, resulting in simpler spectra with less isotopic splitting.

Chlorine isotopes exist as 35Cl and 37Cl in a 3:1 ratio, while bromine isotopes exist as 79Br and 81Br in a 1:1 ratio. The mass spectrum of alkyl halides ...

Electrospray Ionization (ESI) Mass Spectrometry

Higher molecular weight biomolecules are nonvolatile compounds that may decompose before ionizing or vaporizing during mass analysis with conventional electron impact ionization methods. Accordingly, electrospray ionization (ESI) is the favored method for vaporizing and ionizing biomolecules as it circumvents rapid fragmentation and enables the recording of mass signals for the entire biomolecule.
ESI utilizes electrical energy to transfer ions from the liquid phase of the sample into the gaseous phase. The analyte biomolecule is premixed with an ionic liquid&#8212;a nonmolecular compound serving as the ionization source. The solution is sprayed through a high-voltage capillary to generate a fine aerosol. The voltage difference applied between the capillary and the entrance of the analysis chamber causes the movement of charged droplets toward the analysis chamber. The ionic liquid from the aerosol evaporates during this movement, leaving behind a variably protonated or ionized analyte molecule. These charged species are detected in the mass spectrum at an m/z value equivalent to the sum of the analyte molecule&#39;s molecular mass and the ions&#39; molecular weight from the ionic liquid associated with the analyte molecule.
The position of mass signals varies depending on the type of cations present in the ionic liquid. For example, the presence of sodium ions in the ionic liquid leads to an (M+23) peak in the mass spectra, while the presence of a proton results in an (M+1) peak.

Higher molecular weight biomolecules are nonvolatile compounds that may decompose before ionizing or vaporizing during mass analysis with conventional ...

Matrix-Assisted Laser Desorption Ionization (MALDI)

Matrix-assisted laser desorption ionization (MALDI) is a powerful analytical technique used in mass spectrometry. It enables the identification and characterization of various biomolecules, including proteins, peptides, nucleic acids, and carbohydrates. MALDI spectrometry is widely employed in biological and medical research, as well as in fields like pharmacology and biochemistry.
The analyte of interest, a biomolecule or a mixture of biomolecules, is mixed with a suitable matrix material. The matrix is usually an organic compound, such as a small organic acid or a crystalline substance, that facilitates ionization. This analyte-matrix mixture is then deposited onto a target surface, inserted into the mass spectrometer, and dried. During drying, the matrix forms small crystals that incorporate the analyte molecules within their structure.
Once the sample is prepared, a pulsed laser is directed onto the target surface. The matrix molecules absorb the laser beam energy, causing them to heat up and vaporize rapidly. This process is known as laser desorption. As the matrix molecules vaporize, they carry the embedded analyte molecules. The vaporized analyte molecules become ionized through a process called proton transfer. The proton transfer occurs between the matrix and the analyte molecule. The matrix molecule donates a proton to the analyte molecule, resulting in the formation of protonated ions. The analyte ions are then accelerated by an electric field and further separated based on their mass-to-charge ratio in a time-of-flight mass analyzer.
The mass spectrum obtained from MALDI spectrometry provides valuable information about the mass and relative abundance of the analyzed biomolecules.

Matrix-assisted laser desorption ionization (MALDI) is a powerful analytical technique used in mass spectrometry. It enables the identification and ...

Mass Spectrometry: Aldehyde and Ketone Fragmentation

In mass spectrometry, the fragmentation of aliphatic aldehydes and ketones generally occurs through three key mechanisms: &#945;-cleavage, inductive cleavage, and the McLafferty rearrangement.
<ol>
	<li>&#945;-Cleavage 
	&#945;-Cleavage is a common fragmentation in carbonyl compounds where the bond adjacent to the carbonyl group is broken. This process produces an alkyl radical and an acylium cation, which is often detected in the mass spectrum due to its stability.</li>
	<li>Inductive Cleavage 
	In inductive cleavage, fragmentation yields an acyl radical and an alkyl cation. This occurs when electrons are drawn toward the carbonyl, weakening adjacent bonds and resulting in a distinctive fragmentation pattern. For example, in the mass spectrum of 5-methyl-2-hexanone, inductive cleavage produces an alkyl cation at a mass-to-charge (m/z) ratio of 71.</li>
	<li>McLafferty Rearrangement 
	The McLafferty rearrangement is a specific fragmentation pattern for carbonyl compounds with &#947;-hydrogen (hydrogen on the third carbon from the carbonyl group). The molecule undergoes a six-membered cyclic transition in this rearrangement, yielding a radical cation and a neutral alkene. For 5-methyl-2-hexanone, this rearrangement results in a peak at m/z 58.</li>
</ol>
Example: Fragmentation of 5-methyl-2-hexanone 
In the mass spectrum of 5-methyl-2-hexanone, the molecular ion undergoes these fragmentation patterns:
<ol style="list-style-type: circle;">
	<li>Inductive cleavage produces an alkyl cation at m/z 71.</li>
	<li>&#945;-Cleavage results in the base peak at m/z 43.</li>
	<li>McLafferty rearrangement creates a distinct peak at m/z 58.</li>
</ol>
An additional diagnostic feature in aldehydes is the M&#8722;1 peak, which arises due to the &#945;-cleavage of the aldehyde proton. In mass spectrometric analysis, this peak can help identify aldehydes, specifically among other carbonyl compounds.
Understanding these fragmentation pathways is crucial for interpreting mass spectra, particularly in identifying functional groups and distinguishing between similar compounds.

In mass spectrometry, the fragmentation of aliphatic aldehydes and ketones generally occurs through three key mechanisms: &#945;-cleavage, inductive ...

Mass Spectrometry: Alcohol Fragmentation

Alcohols (R-OH) ionize to lose one non-bonded electron from the oxygen atom, forming molecular ions. Due to their tendency to fragment rapidly, the intensity of the molecular ion peak in the mass spectrum is weak or sometimes absent. The fragmentation patterns for alcohols occur in two ways, i.e. &#9082;-cleavage and dehydration. During &#9082;-cleavage, the bond at the &#9082;-position adjacent to the hydroxyl group cleaves to give a resonance-stabilized cation and a radical. However, intramolecular dehydration involves losing a water molecule from an alcohol, forming an alkene cation, which shows a peak at M&#8722;18. Consider the fragmentation of butanol as shown below. &#9082;-cleavage produces a base peak at a mass-to-charge ratio of 31. In the case of dehydration, the fragmentation forms an alkene radical cation at a mass-to-charge ratio of 56.
<img alt="Figure1" src="/files/ftp_upload/13046/13046-PT_Figure_1.svg" style="text-align: center; height: 175px;" />

Alcohols (R-OH) ionize to lose one non-bonded electron from the oxygen atom, forming molecular ions. Due to their tendency to fragment rapidly, the ...

Mass Spectrometry: Amine Fragmentation

Amines can be identified using mass spectroscopy based on their characteristic fragmentation patterns. The molecular ions of amines undergo fragmentation via &#9082;-cleavage. The &#9082;-cleavage of the carbon-carbon bonds in amines generates an alkyl radical and resonance-stabilized nitrogen-containing cation.
In amines, the number of nitrogen atoms affects the mass of the molecular ion, which is described by the nitrogen rule of mass spectrometry. This rule states that a compound containing a single or an odd number of nitrogen atoms produces a molecular ion with an odd molecular weight, while a compound with no or an even number of nitrogen atoms generates a molecular ion with an even molecular weight.
For example, the mass spectrum of 3-methyl-1-butanamine, which contains one nitrogen atom, displays a molecular ion having an odd mass-to-charge ratio of 87. Fragmentation of this molecular ion via &#9082;-cleavage produces a base peak, which features a mass signal at a mass-to-charge ratio of 30, corresponding with the loss of the 2-methyl propyl radical.
Similarly, the fragmentation of triethylamine via &#9082;-cleavage generates a cation at a mass-to-charge ratio of 86. The molecular ion peak shows an odd mass-to-charge ratio of 101, as shown below.
<img alt="Figure1" src="/files/ftp_upload/13048/13048_PT_Figure_1.svg" style="text-align: center; height: 105px;" />

Amines can be identified using mass spectroscopy based on their characteristic fragmentation patterns. The molecular ions of amines undergo fragmentation ...

Mass Spectrometry: Cycloalkene Fragmentation

The molecular ions of cycloalkenes undergo fragmentation via a retro-Diels&#8211;Alder reaction.

The reaction proceeds via the cleavage of two carbon-carbon bonds in the cycloalkene to yield ethene. The remaining part of the cycloalkene structure is a dienyl radical cation with a molecular weight of 28 u lower than the molecular ion. This fragmentation pathway is similar to the fragmentation of cycloalkanes releasing ethene, differing only in the resultant radical cation. An alkyl species forms from the cycloalkane, whereas a dienyl species originates from the cycloalkene.

Retro-Diels&#8211;Alder reactions of cycloalkenes are also similar to the McLafferty-rearrangement-type fragmentation observed in acyclic alkenes with hydrogen on the &#947; carbon. In both cases, cleavage occurs at two positions, yielding an ethene molecule and an alkenyl species. In acyclic alkenes, the cleavage occurs at one carbon-carbon bond and a carbon-hydrogen bond, along with rearranging hydrogen from one carbon to another. In cyclic alkenes, cleavage occurs at two carbon&#8211;carbon bonds without any atomic rearrangement. Figure 1 depicts the fragmentation of cyclohexene via a retro-Diels&#8211;Alder reaction.
<img alt="Figure1" src="/files/ftp_upload/13044/13044-PT_Figure_1.svg" style="text-align: center; height: 90px;" />
Figure 1: Fragmentation of cyclohexene via a retro-Diels&#8211;Alder reaction.
In addition to the retro-Diels&#8211;Alder reaction, branched cycloalkenes exhibit fragmentation via cleavage of the side chain to form a cycloalkene cation. For example, the fragmentation of 1-methyl-1-cyclohexene via a retro-Diels&#8211;Alder reaction and side-chain cleavage are shown in Figure 2.
<img alt="Figure2" src="/files/ftp_upload/13044/13044-PT_Figure_2.svg" style="text-align: center; height: 225px;" />
Figure 2: Fragmentation of 1-methyl-1-cyclohexene via (top) a retro-Diels&#8211;Alder reaction; (bottom) side-chain cleavage.
The corresponding signals of the isoprenyl radical cation and the cyclohexenyl cation are evident in the mass spectrum of 1-methyl-1-cyclohexene shown in Figure 3.
<img alt="Figure3" src="/files/ftp_upload/13044/13044-PT_Figure_3.svg" style="text-align: center; height: 250px;" />
Figure 3: Mass spectrum of 1-methyl-1-cyclohexene.

The molecular ions of cycloalkenes undergo fragmentation via a retro-Diels&#8211;Alder reaction.

The reaction proceeds via the cleavage of two ...

Mass Spectrometry: Alkyne Fragmentation

The fragmentation of alkynes preferentially occurs at the carbon&#8211;carbon bond between the &#945; and &#946; carbon of the alkyne bond to generate a 3-propynyl cation (or propargyl cation). In terminal alkynes, there is the only type of fragmentation that yields the 3-propynyl cation. The unsubstituted 3-propynyl cation exhibits a peak at a mass-to-charge ratio of 39. In internal alkynes, the 3-propynyl cation is substituted. For example, 2-pentyne fragments into methyl-substituted 3-propynyl cation, which subsequently features as a mass signal at the mass-to-charge ratio of 56. The 3-propynyl cation is resonance-stabilized, and the corresponding mass signal is intense in the mass spectrum of alkynes. Figure 1 shows the fragmentation of 1-pentyne into an ethyl radical and a resonance stabilized 3-propynyl cation.
<img alt="Figure1" src="/files/ftp_upload/13045/13045-PT_Figure_1.svg" style="text-align: center; height: 115px;" />
Figure 1: Fragmentation of 1-pentyne molecular ion to yield the 3-propynyl cation.
Another fragmentation pathway observed in terminal alkynes is the loss of hydrogen from the terminal sp carbon. This results in a mass signal with a mass-to-charge ratio of one unit less than the molecular ion. This M&#8211;1 peak is very intense and becomes the base peak in the mass spectra of many alkynes, so it can be used to identify alkynes.
<img alt="Figure2" src="/files/ftp_upload/13045/13045-PT_Figure_2.svg" style="text-align: center; height: 275px;" />
Figure 2: The mass spectrum of 1-pentyne.

The fragmentation of alkynes preferentially occurs at the carbon&#8211;carbon bond between the &#945; and &#946; carbon of the alkyne bond to generate a ...

Mass Spectrometry: Aromatic Compound Fragmentation

Upon ionization, aromatic compounds generate a molecular ion that is observed as a prominent peak in their mass spectra. For example, the molecular ion peak for benzene appears at a mass-to-charge ratio of 78, while toluene is observed at a mass-to-charge ratio of 92. The molecular ion benzene is highly stable and does not readily undergo further fragmentation due to the significant amount of energy required to disrupt the aromatic stability of the benzene ring. In contrast, the molecular ion of alkyl&#8208;substituted benzenes, such as toluene, can undergo fragmentation by losing a hydrogen atom, forming a benzylic carbocation. This carbocation can rearrange to form the resonance-stabilized tropylium cation, which appears in the mass spectra as a strong peak. In the case of toluene, this strong peak is observed at a mass-to-charge ratio of 91.

Upon ionization, aromatic compounds generate a molecular ion that is observed as a prominent peak in their mass spectra. For example, the molecular ion ...

Mass Spectrometry: Long-Chain Alkane Fragmentation

The molecular ions of linear alkanes prefer to fragment at the carbon-carbon bond away from the end of the chain since the cleavage of an inner bond creates a stable carbocation and a stable radical. Consequently, the mass signals of linear alkanes feature intense peaks in the middle of the mass-to-charge ratio plot with weaker peaks on either end. The fragmentation of each carbon-carbon bond with the release of a methyl group in each splitting leads to prominent peaks in the mass spectra separated by 14 u. Smaller mass signals near each prominent peak result arise from secondary fragmentation at the carbon-hydrogen bond.
For example, consider the fragmentation pattern of n-hexane shown in Figure 1 and the corresponding mass spectra in Figure 2.
<img alt="Figure1" src="/files/ftp_upload/12299/12299-PT_Figure_1.svg" style="text-align: center; height: 500px;" />
Figure 1: Fragmentation of n-hexane molecular ion.
<img alt="Figure2" src="/files/ftp_upload/12299/12299-PT_Figure_2.svg" style="text-align: center; height: 275px;" />
Figure 2: Mass spectrum of n-hexane.
The signals at a mass-to-charge ratio of 71, 57, 43, 29, and 15 indicate that the cleavage can occur at all carbon-carbon bonds in the molecule. However, the relative abundance of these peaks varies. The difference between molecular ion signal and signal at 71 indicates the separation of methyl groups (M.W. = 15 u) group from molecular ions. Further release of a CH2 group from that fragment (M.W. = 14 u) results in a signal at 57. The signals at 43, 29, and 15 are due to the subsequent releases of CH2 groups. The abundance of signals at 15 and 71 is minimal due to the least probability for the formation of unstable methyl carbocation or a methyl radical, respectively. The base peak at 43 indicates the most preferred fragmentation, which yields a pair of stable carbocation and radical.

The molecular ions of linear alkanes prefer to fragment at the carbon-carbon bond away from the end of the chain since the cleavage of an inner bond ...

Electric Fields

Source: Yong P. Chen, PhD, Department of Physics &#38; Astronomy, College of Science, Purdue University, West Lafayette, IN
An electric field is generated by a charged object (referred to as the source charge) in the space around it, and represents the ability to exert electric force on another charged object (referred to as the test charge). Represented by a vector at any given point in the space, the electric field is the electrical force per unit test charge placed at that point (the force on an arbitrary charge would be the charge times the electric field). The electric field is fundamental to electricity and effects of charges, and it is also closely related to other important quantities such as electrical voltage.
This experiment will use electrified powders in an oil that line up with electric fields produced by charged electrodes to visualize the electric field lines. This experiment will also demonstrate how an electric field can induce charges and how charges respond to the electric field by observing the effect of a charged rod on a nearby soda can.

Electric Fields and Electric Charges

電界

Source: Yong P. Chen, PhD, Department of Physics &#38; Astronomy, College of Science, Purdue University, West Lafayette, IN
An electric field is generated ...

Electric Potential

Source: Yong P. Chen, PhD, Department of Physics &#38; Astronomy, College of Science, Purdue University, West Lafayette, IN
Electric potential, also known as &#34;voltage&#34;, measures the electric potential energy per unit charge. Electric field is a scalar quantity and is fundamental to many electrical effects. Like potential energy, what is physically meaningful is the difference in the electric potential. For example, the spatial variation in the electric potential is related to the electric field, which gives rise to the electric force on a charge. The difference in the electric potential between two points in a resistor drives the electric current flow.
This experiment will use both a volt meter and a fluorescent tube to demonstrate the electric potential (more accurately, the potential difference between two points in space) generated by a charged sphere. The experiment will demonstrate the concept of equipotential surfaces, which are perpendicular to the electric fields.

Electric Potential and Voltage

電位

Source: Yong P. Chen, PhD, Department of Physics &#38; Astronomy, College of Science, Purdue University, West Lafayette, IN
Electric potential, also known ...

Magnetic Fields

Source: Yong P. Chen, PhD, Department of Physics &#38; Astronomy, College of Science, Purdue University, West Lafayette, IN
Magnetic fields can be generated by moving charges, such as an electrical current. The magnetic field generated by a current can be calculated from the Maxwell equation. In addition, magnetic objects such as bar magnets can also generate magnetic fields due to microscopic dynamics of charges inside the material. Magnetic fields will exert magnetic force on other moving charges or magnetic objects, with the force proportional to the magnetic field. Magnetic fields are fundamental to electromagnetism and underlie many practical applications ranging from compasses to magnetic resonance imaging.
This experiment will demonstrate magnetic fields produced by a permanent bar magnet as well as an electrical current, using small compass needle magnets that align with magnetic fields. This experiment will also demonstrate the force exerted by the magnetic fields produced by a current on another current-carrying wire.

Effect of Magnetic Fields and Lorentz Force

磁場

Source: Yong P. Chen, PhD, Department of Physics &#38; Astronomy, College of Science, Purdue University, West Lafayette, IN
Magnetic fields can be ...

Electric Charge in a Magnetic Field

Source: Andrew Duffy, PhD, Department of Physics, Boston University, Boston, MA
This experiment duplicates J.J. Thomson's famous experiment at the end of the 19th century, in which he measured the charge-to-mass ratio of the electron. In combination with Robert A. Millikan's oil-drop experiment a few years later that produced a value for the charge of the electron, the experiments enabled scientists to find, for the first time, both the mass and the charge of the electron, which are key parameters for the electron.
Thomson was not able to measure the electron charge or the electron mass separately, but he was able to find their ratio. The same is true for this demonstration; although here there is the advantage of being able to look up the values for the magnitude of the charge on the electron(e) and the mass of the electron (me), which are now both known precisely.

磁場下における電荷

Source: Andrew Duffy, PhD, Department of Physics, Boston University, Boston, MA
This experiment duplicates J.J. Thomson's famous experiment at the end of ...

Investigation Ohm's Law for Ohmic and Nonohmic Conductors

Source: Andrew Duffy, PhD, Department of Physics, Boston University, Boston, MA
This experiment investigates Ohm's law, which relates current, voltage, and resistance.
One goal of the experiment is to become familiar with circuit diagrams and the terminology involved in basic circuits, such as resistor, resistance, current, voltage, and power supply. By the end of the experiment, familiarity is gained with how to wire up a circuit and how to measure both the current passing through a circuit component and the potential difference, or voltage, across it.
In a circuit, a battery or power supply provides a voltage measured in volts (V) that makes the charge flow. Other elements in the circuit, such as light bulbs or resistors (which are often just long narrow wires wound into coils) limit the rate at which the charge flows. The rate of flow of the charge is known as current measured in amperes (A), or amps for short, and the degree to which resistors and light bulb filaments limit the flow is known as their resistance measured in ohms (&#937;). This experiment involves an exploration of Ohm's law, which relates voltage, current, and resistance. 
This experiment also explores the difference between a basic circuit component called a resistor, and a light bulb and a light-emitting diode (LED). Light bulbs and LEDs are part of many common devices and are used for various lighting applications, and so it is useful to understand how they work.

Ohm&#039;s Law for Ohmic and Nonohmic Resistors

オームの法則

Source: Andrew Duffy, PhD, Department of Physics, Boston University, Boston, MA
This experiment investigates Ohm's law, which relates current, voltage, ...

Series and Parallel Resistors

Source: Yong P. Chen, PhD, Department of Physics &#38; Astronomy, College of Science, Purdue University, West Lafayette, IN
This experiment demonstrates how current is distributed in resistors connected in series or parallel, and thus describes how to calculate the total &#34;effective&#34; resistance. Using Ohm&#39;s law, it possible to convert between the voltage and current through a resistance, if the resistance is known.
For two resistors connected in series, (meaning that they are wired one after the other), the same current will flow through them. The voltages will add up to a &#34;total voltage&#34;, and thus, the total &#34;effective resistance&#34; is the sum of the two resistances. This is sometimes called a &#34;voltage divider&#34; because the total voltage is divided between the two resistors in proportion to their individual resistances.
For two resistors connected in parallel, (meaning that they are both wired between two shared terminals), the current is split between the two while they share the same voltage. In this case, the reciprocal of the total effective resistance will equal the sum of the reciprocals of the two resistances.
Series and parallel resistors are a key component to most circuits and influence how electricity is used in most applications.

Series and Parallel Resistors and Light Bulbs Experiment

シリーズと並列抵抗

Source: Yong P. Chen, PhD, Department of Physics &#38; Astronomy, College of Science, Purdue University, West Lafayette, IN
This experiment demonstrates ...

Capacitance

Source: Yong P. Chen, PhD, Department of Physics &#38; Astronomy, College of Science, Purdue University, West Lafayette, IN
This experiment will use commercial capacitors and a parallel plate capacitor to demonstrate the concept of capacitance. A capacitor stores opposite charges on two conductors, for example two opposite metal plates, leading to a potential difference (voltage drop) between the two conductors. The amount of charge on each conductor is proportional to this voltage drop, with the capacitance as the proportionality factor. If the voltage is changing with time, the current flowing into the capacitor will be proportional to the rate of that change, and again the capacitance is the proportionality factor.
The capacitance of the parallel plate capacitor is the product of the dielectric constant with the distance between the plates divided by the area of the plate. This experiment will demonstrate the proportionality with distance by first depositing some charge onto the capacitor and then using a high-impedance voltmeter (electrometer) to monitor the voltage between the plates as the distance is increased. The voltage change will also be monitored with a dielectric material, such as a plastic plate inserted into the space between the metal plates.
A capacitance meter will be used to directly measure the capacitance, as well as to measure parallel and series connections of commercially-available capacitors and to study how the total capacitance is related to individual capacitances.

Capacitance and the Principle of Parallel Plate Capacitors

静電容量

Source: Yong P. Chen, PhD, Department of Physics &#38; Astronomy, College of Science, Purdue University, West Lafayette, IN
This experiment will use ...

Inductance

Source: Yong P. Chen, PhD, Department of Physics &#38; Astronomy, College of Science, Purdue University, West Lafayette, IN
This experiment will use inductive coils to demonstrate the concept of inductor and inductance. Magnetic induction will be demonstrated using a rod magnet inserted into or extracted away from the core of a coil to induce a transient electromotive force (emf) voltage in the coil, measured by a voltmeter. This experiment will also demonstrate the mutual inductance between two coils, where turning on or off a current flowing in a coil can induce an emf voltage in a second coil nearby. Finally, the experiment will demonstrate the self-inductance of a coil, when switching a current off induces an emf to light up a light bulb connected in parallel with the coil.

Magnetic Induction, Inductors and Inductance

インダクタンス

RC/RL/LC Circuits

Source: Yong P. Chen, PhD, Department of Physics &#38; Astronomy, College of Science, Purdue University, West Lafayette, IN
Capacitors (C), inductors (L), and resistors (R) are each an important circuit element with distinct behaviors. A resistor dissipates energy and obeys Ohm&#39;s law, with its voltage proportional to its current. A capacitor stores electrical energy, with its current proportional to the rate of change of its voltage, while an inductor stores magnetic energy, with its voltage proportional to the rate of change of its current. When these circuit elements are combined, they can cause the current or voltage to vary with time in various, interesting ways. Such combinations are commonly used to process time- or frequency-dependent electrical signals, such as in alternating current (AC) circuits, radios, and electrical filters. This experiment will demonstrate the time-dependent behaviors of the resistor-capacitor (RC), resistor-inductor (RL), and inductor-capacitor (LC) circuits. The experiment will demonstrate the transient behaviors of RC and RL circuits using a light bulb (resistor) connected in series to a capacitor or inductor, upon connecting to (and switching on) a power supply. The experiment will also demonstrate the oscillatory behavior of an LC circuit.

Resistor-capacitor, Resistor-inductor and Inductor-capacitor Circuits

RC/RL/LC 回路

Source: Yong P. Chen, PhD, Department of Physics &#38; Astronomy, College of Science, Purdue University, West Lafayette, IN
Capacitors (C), inductors (L), ...

Semiconductors

Source: Derek Wilson,&#160;Asantha Cooray, PhD, Department of Physics &#38; Astronomy, School of Physical Sciences, University of California, Irvine, CA
Semiconductors are materials whose ability to conduct an electrical current depends strongly on their temperature and level of impurity. The most common type of semiconductor material is crystalline silicon. Most pure semiconductors are not outstanding conductors; to improve conductivity, a pure semiconductor is often combined or &#34;doped&#34; with an impurity. These impurities are either donors, like phosphorus and arsenic, that donate electrons to the silicon, or acceptors, like boron and aluminum, that steal electrons from the silicon. When acceptors take electrons from the silicon, they leave regions of positive charge called &#34;holes&#34; that effectively behave as positively charged electrons.
A p-type semiconductor is formed when doping makes holes that are the dominant charge carrier in the material. An n-type semiconductor is formed when a semiconductor is doped such that the dominant charge carrier is the electron. As one might expect, a p-n junction is formed at the boundary between the p-type semiconductor and n-type semiconductor. The interaction of electrons and holes at the junction gives rise to the remarkable behavior seen in circuit components such as diodes and transistors. This lab will explore the properties of a single p-n junction in the form of a semiconductor diode.

Semiconductors and Characteristics of P-N Junctions

半導体

Source: Derek Wilson,&#160;Asantha Cooray, PhD, Department of Physics &#38; Astronomy, School of Physical Sciences, University of California, Irvine, CA
...

Photoelectric Effect

Source: Yong P. Chen, PhD, Department of Physics &#38;&#38; Astronomy, College of Science, Purdue University, West Lafayette, IN
Photoelectric effect refers to the emission of electrons from a metalwhen light is shining on it. In order for the electrons to be liberated from the metal, the frequency of the light needs to be sufficiently high such that the photons in the light have sufficient energy. This energy is proportional to the light frequency.The photoelectric effect provided the experimental evidence for the quantum of light that is known as photon.
This experiment will demonstrate the photoelectric effect using a charged zinc metal subject to either a regular lamp light, or ultraviolet (UV) light with higher frequency and photon energy.The zinc plate will be connected to an electroscope, an instrument that can read the presence and relative amount of charges. The experiment will demonstrate that the UV light, but not the regular lamp, can discharge the negatively charged zinc by ejecting its excess electrons.Neither light source, however, can discharge positively charged zinc, consistent with the fact that electrons that are emitted in photoelectric effect.

Photons and Photoelectric Effect

光電効果

Source: Yong P. Chen, PhD, Department of Physics &#38;&#38; Astronomy, College of Science, Purdue University, West Lafayette, IN
Photoelectric effect ...

Reflection and Refraction

Source: Derek Wilson,&#160;Asantha Cooray, PhD, Department of Physics &#38; Astronomy, School of Physical Sciences, University of California, Irvine, CA
Light travels at different speeds depending on the material through which it is propagating. When light travels from one material to another, it will either slow down or speed up. In order to conserve energy and momentum, the light must change the direction in which it propagates. This bending of light is known as refraction. Some fraction of the light is also reflected at the interface between the two materials. In special cases, a light beam can be refracted so sharply at an interface that it is actually completely reflected back into the medium from which it was coming.
Lenses make use of the principle of refraction. Lenses come in two varieties with different curvatures: convex lenses and concave lenses. Convex lenses are often used to focus light but can also be used to create magnified images of objects. When a convex lens causes the light rays coming from an object to diverge, the human eye judges the light to be coming from some point behind the actual object from which the light is originating. The image of the object will in this case be magnified. This type of image is called a virtual image. Concave lenses can also cause light rays to diverge and create virtual images, though the image will be demagnified.
This lab will demonstrate the fundamental law of refraction and will examine the ways in which lenses create images.

Reflection; Refraction; Snell&#039;s Law and Total Internal Reflection

反射と屈折

Interference and Diffraction

Source: Yong P. Chen, PhD, Department of Physics &#38; Astronomy, College of Science, Purdue University, West Lafayette, IN
Interference and diffraction are characteristic phenomena of waves, ranging from water waves to electromagnetic waves such as light. Interference refers to the phenomenon of when two waves of the same kind overlap to give an alternating spatial variation of large and small wave amplitude. Diffraction refers to the phenomenon of when a wave passes through an aperture or goes around an object, different parts of the wave can interfere and also give rise to a spatial alternation of large and small amplitude.
This experiment will demonstrate the wave nature of the light by observing diffraction and interference of a laser light passing through a single slit and double slits, respectively. The slits are simply cut using razor blades in an aluminum foil and the characteristic diffraction and interference patterns manifest as patterns of alternating light and dark fringes on a screen placed after the foil, when the light is shone through the slit(s) on the foil. Historically, the observation of diffraction and interference of light played important roles in establishing that light is an electromagnetic wave.

Interference; Diffraction; Single and Double Slit Experiments

干渉と回折

Source: Yong P. Chen, PhD, Department of Physics &#38; Astronomy, College of Science, Purdue University, West Lafayette, IN
Interference and diffraction ...

Standing Waves

Source: Arianna Brown,&#160;Asantha Cooray, PhD,&#160;Department of Physics &#38; Astronomy, School of Physical Sciences, University of California, Irvine, CA
Standing waves, or stationary waves, are waves that appear not to propagate and are produced by the interference of two waves traveling in opposite directions with the same frequency and amplitude. These waves appear to vibrate up and down with no linear movement and are most easily identified in vibrating finite media like a plucked guitar string, water in a lake, or air in a room. For example, if a string is fixed at both ends and two identical waves are&#160;sent traveling along the length, the first wave will hit the end barrier and reflect back in the opposite direction, and the two waves will superpose to produce a standing wave. This motion is periodic with frequencies defined by the length of the medium and is a visual example of simple harmonic motion. Simple harmonic motion is motion that oscillates or is periodic, where the restoring force is proportional to the displacement, meaning the farther something is pushed, the harder it pushes back.
The goal of this experiment is to understand the roles of wave superposition and reflection in creating standing waves, and exploit those concepts to calculate the first few resonant frequencies, or harmonics, of standing waves on a slinky. Each frequency that an object produces has its own standing wave patterns, where the wave with the lowest possible frequency is called the fundamental frequency. A harmonic is a wave that has a frequency proportionate to the fundamental frequency by whole integer numbers.

Standing/Stationary Waves and Simple Harmonics

定在波

Source: Arianna Brown,&#160;Asantha Cooray, PhD,&#160;Department of Physics &#38; Astronomy, School of Physical Sciences, University of California, ...

Sound Waves and Doppler Shift

Source: Arianna Brown,&#160;Asantha Cooray, PhD, Department of Physics &#38; Astronomy, School of Physical Sciences, University of California, Irvine, CA
Waves are disturbances that propagate through a material medium or empty space. Light waves can travel through a vacuum and some forms of matter, and are transverse in nature, which means that the oscillations are perpendicular to the direction of propagation. However, sound waves are pressure waves that travel through an elastic medium like air, and are longitudinal in nature, which means the oscillations are parallel to the direction of propagation. When sound is introduced to a medium by a vibrating object, like the vocal chords of a person or strings in a piano, the particles in the air experience forward and backward motion as the vibrating object moves forward and backward. This results in regions in the air where the air particles are compressed together, called compressions, and other regions where they are spread apart, called rarefactions. The energy created by a sound wave oscillates between the potential energy created by the compressions and the kinetic energy of the small movements and speeds of the particles of the medium.
Compressions and rarefactions can be used to define the relationship between sound wave velocity and frequency. The goal of this experiment is to measure the speed of sound in air and explore the apparent change in frequency for an object emitting sound waves while in motion, called the Doppler effect.

Sound Waves, Doppler Effect and Measuring the Speed of Sound

音の波とドップラー シフト

Source: Arianna Brown,&#160;Asantha Cooray, PhD, Department of Physics &#38; Astronomy, School of Physical Sciences, University of California, Irvine, CA
...

Education Physics Ii

Science Education (物理学)

Science Education (物理学)

Science Education (物理学)

Science Education (物理学)

Science Education (物理学)

Science Education (物理学)

Science Education (物理学)

Science Education (物理学)

Science Education (物理学)

Science Education (物理学)

Science Education (物理学)

Science Education (物理学)

Science Education (物理学)

Science Education (物理学)

Science Education (物理学)

Education Physics Ii

@media screen and (min-width: 320px){.css-u03n47{font-size:var(--chakra-fontSizes-xs);}}Science Education (物理学)

Science Education (物理学)

Science Education (物理学)

Science Education (物理学)

Science Education (物理学)

Science Education (物理学)

Science Education (物理学)

Science Education (物理学)

Science Education (物理学)

Science Education (物理学)

Science Education (物理学)

Science Education (物理学)

Science Education (物理学)

Science Education (物理学)

Science Education (物理学)

Science Education (物理学)