CL-37/CL-35 ISOTOPE EFFECTS IN C-13-NMR SPECTROSCOPY OF CHLOROHYDROCARBONS
CL-37/CL-35 ISOTOPE EFFECTS IN C-13-NMR SPECTROSCOPY OF CHLOROHYDROCARBONS
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DOI：
10.1002/mrc.1260310111
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发表时间：
1993-01-01
影响因子：
2
通讯作者：
HARRIS, KDM
中科院分区：
文献类型：
--
作者：
ALIEV, AE;HARRIS, KDM
在氯代烃中，同位素对与Cl-35和C-37直接键合的C-13化学位移的影响已被广泛报道。通过在复合脉冲H-1去耦条件下记录C-13 NMR谱，可以获得足够窄的C-13共振，以允许由于Cl-35/Cl-37同位素效应而在环境温度下分辨几ppb量级的非常小的分裂。对这一现象的观察允许常规识别由于碳原子直接键合到氯的C-13共振，因为对于天然丰度样品，同位素效应将C-13信号分成具有特征强度分布的一组线。阐明了影响同位素效应大小的各种结构特征，并讨论了同位素效应的温度依赖性。从低温C-13核磁共振谱氯环己烷，同位素位移的碳原子直接键合到氯分别测量轴向和赤道构象。测量值表明，轴向构象的同位素位移较大。
Isotope effects on the chemical shift of C-13 directly bonded to the isotopes Cl-35 and C-37 are reported for a wide range of chlorohydrocarbons. By recording C-13 NMR spectra under conditions of composite pulse H-1 decoupling, C-13 resonances can be obtained that are sufficiently narrow to allow the very small splittings of the order of a few ppb due to the Cl-35/Cl-37 isotope effect to be resolved at ambient temperature. Observation of this phenomenon allows the routine identification of C-13 resonances due to carbon atoms directly bonded to chlorine, since, for natural abundance samples, the isotope effect splits the C-13 signal into a set of lines with a characteristic intensity distribution. Various structural features influencing the magnitude of the isotope effect have been elucidated, and the temperature dependence of the isotope effect is also discussed. From low-temperature C-13 NMR spectra for chlorocyclohexane, isotope shifts for the carbon atom directly bonded to chlorine were measured separately for the axial and equatorial conformations. The measured values indicate that the isotope shift is larger for the axial conformation.