碳-13核磁共振Carbon-13 nuclear magnetic resonance

¹²C 无核自旋，¹³C 天然丰度仅 1.1%，磁旋比约为 ¹H 的 1/4，因此灵敏度只有 ¹H 的约 1/5700，需要较多样品和长时间累加。化学位移范围宽（0–220 ppm），谱峰很少重叠：饱和碳 0–60，与 O/N 相连碳 40–90，炔碳 65–90，烯碳和芳碳 100–160，腈 115–125，羰基 160–220（羧酸及衍生物 160–185，醛酮 190–220）。通常采用宽带质子去耦，使每种碳只显示一条单峰；由于 ¹³C 丰度低，¹³C–¹³C 耦合可忽略。

¹²C has no spin, ¹³C is only 1.1% abundant, and its magnetogyric ratio is about a quarter of ¹H's, so sensitivity is about 1/5700 that of ¹H and more sample and longer accumulation are needed. The shift range is wide (0–220 ppm) and peaks rarely overlap: saturated carbons 0–60, carbons attached to O or N 40–90, alkyne carbons 65–90, alkene and aromatic carbons 100–160, nitriles 115–125, and carbonyls 160–220 (acids and derivatives 160–185, aldehydes and ketones 190–220). Broadband proton decoupling usually gives one singlet per kind of carbon, and ¹³C–¹³C coupling is negligible at natural abundance.

去耦时的核欧沃豪斯效应（NOE）使连氢碳信号增强，所以常规碳谱峰面积不能直接定量，季碳信号较弱。无畸变极化转移增强（DEPT）可区分 CH₃、CH₂、CH 和季碳：DEPT-135 中 CH 和 CH₃ 为正峰、CH₂ 为负峰、季碳不出峰。门控去耦可得到定量碳谱。

The nuclear Overhauser effect (NOE) during decoupling enhances carbons bearing hydrogens, so routine carbon spectra are not quantitative and quaternary carbons appear weak. DEPT (distortionless enhancement by polarisation transfer) distinguishes CH₃, CH₂, CH and quaternary carbons: in DEPT-135, CH and CH₃ point up, CH₂ down, and quaternary carbons vanish. Inverse-gated decoupling gives quantitative carbon spectra.

1957 年劳特伯和霍尔姆首次报道 ¹³C NMR 谱，但信号极弱难以实用。1960 年代末傅里叶变换 NMR 技术和计算机累加使 ¹³C NMR 成为常规手段。劳特伯后来因发明磁共振成像获 2003 年诺贝尔生理学或医学奖。

Lauterbur and Holm first reported ¹³C NMR spectra in 1957, but the signals were too weak to be practical. Fourier-transform NMR and computer averaging in the late 1960s made it routine. Lauterbur later shared the 2003 Nobel Prize in Physiology or Medicine for inventing magnetic resonance imaging.