Proton (¹H) NMR Spectroscopy | 质子核磁共振波谱

📚 Proton (¹H) NMR Spectroscopy | 质子核磁共振波谱

Proton nuclear magnetic resonance (¹H NMR) spectroscopy is a powerful analytical technique that uses the magnetic properties of hydrogen nuclei to reveal the structure of organic molecules. In A-Level chemistry, it is used alongside IR and mass spectrometry to determine carbon skeletons, functional groups and the positions of hydrogen atoms.

质子核磁共振（¹H NMR）波谱是一种强大的分析技术，利用氢核的磁性质揭示有机分子的结构。在 A-Level 化学中，它与红外光谱和质谱联用，用来确定碳骨架、官能团和氢原子的位置。

1. What Is Proton NMR? | 什么是质子核磁共振？

In proton NMR, a sample is placed in a strong magnetic field and irradiated with radio waves. Hydrogen nuclei (protons) absorb energy at characteristic frequencies and the instrument records this absorption. The resulting spectrum plots absorption intensity against a chemical shift scale, giving information about the number, type and connectivity of hydrogen atoms.

在质子核磁共振中，样品置于强磁场中并用无线电波照射。氢核（质子）在特征频率处吸收能量，仪器记录这种吸收。所得谱图以吸收强度对化学位移标尺作图，提供氢原子数量、类型和连接方式的信息。

Because almost all organic compounds contain hydrogen, ¹H NMR is extremely versatile. It can distinguish between protons in different chemical environments, for example CH₃, CH₂, OH and aromatic protons.

由于几乎所有有机化合物都含有氢，¹H NMR 非常通用。它可以区分不同化学环境中的质子，例如 CH₃、CH₂、OH 和芳香质子。

2. Nuclear Spin and Magnetic Alignment | 核自旋与磁取向

A proton possesses a property called nuclear spin, with spin quantum number I = ½. When placed in an external magnetic field B₀, its magnetic moment can align either with the field (lower energy, α-state) or against the field (higher energy, β-state).

质子具有称为核自旋的性质，自旋量子数 I = ½。置于外磁场 B₀ 中时，其磁矩可以顺着磁场排列（能量较低，α 态），也可以逆着磁场排列（能量较高，β 态）。

The energy difference between these two states is proportional to the strength of the applied magnetic field. A stronger magnet increases the separation and therefore improves both sensitivity and resolution.

这两个状态之间的能量差与外加磁场强度成正比。更强的磁体使能级间隔增大，从而提高灵敏度和分辨率。

3. The Resonance Condition | 共振条件

When radiofrequency radiation provides a photon whose energy exactly matches the energy gap, the proton absorbs the photon and flips from the lower to the higher spin state. This condition is called resonance.

当射频辐射提供的光子能量恰好等于能级差时，质子吸收光子，从低自旋态跃迁到高自旋态。这一条件称为共振。

ΔE = hν = γhB₀ / 2π

Here ΔE is the energy gap, h is Planck’s constant, ν is the radiofrequency, γ is the magnetogyric ratio of the proton and B₀ is the external magnetic field strength. The spectrometer detects the frequency at which absorption occurs.

其中 ΔE 是能级差，h 是普朗克常数，ν 是射频频率，γ 是质子的磁旋比，B₀ 是外磁场强度。仪器检测发生吸收的频率。

4. Chemical Shift and the δ Scale | 化学位移与 δ 标尺

Not all protons absorb at the same frequency because electrons around the nucleus create small local magnetic fields that oppose the external field. This shielding effect shifts the resonance frequency depending on the chemical environment.

并非所有质子的吸收频率都相同，因为核周围的电子会产生与外磁场相反的局部磁场。这种屏蔽

Published by TutorHao | A-Level Chemistry Revision Series | aleveler.com

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