Low-Temperature 13C Magnetic Resonance. 9.Steric Effects for Methyl Chemical Shift Tensors in Methylcyclohexanes
Low-Temperature 13C Magnetic Resonance. 9.Steric Effects for Methyl Chemical Shift Tensors in Methylcyclohexanes
复制标题
低温 13C 磁共振。
DOI：
10.1021/ja00137a020
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发表时间：
1995
影响因子：
15
通讯作者：
D. Grant
中科院分区：
文献类型：
--
作者：
A.B.T. Soderquist;J. Facelli;W. Horton;D. Grant
本文测量了1-（甲基-13 C）-1-甲基环己烷、顺式-1-（甲基-13 C）-3，5-二甲基环己烷和反式-1-（甲基-13 C）-3，5-二甲基环己烷的固体低温~（13）C NMR谱，并给出了标记甲基碳的~（13）C化学位移张量的主值。化学位移张量的主轴的方向已估计使用从头计算的张量。计算得到的甲基环己烷轴向异构体和赤道异构体的位移张量与3，5-二甲基取代化合物的位移张量基本一致。这表明甲基的化学位移张量主要由局部电子和空间因素决定。环己烷环上的轴向和赤道甲基之间的空间位阻效应和/3-取代基效应的变化进行了讨论，在这些烷烃的化学位移张量的影响。
The solid-state low-temperature 13C NMR spectra of 1-(methyl-13C)-1-methylcyclohexane, cij-l-(methyl-13C)-3, 5-dimethylcyclohexane, and trans-1-(methyl-13C)-3, 5-dimethyIcyclohexane have been measured and the principal values of the 13C chemical shift tensors are reported for the labeled methyl carbons. The orientation of the principal axes of the chemical shift tensor has been estimated using ab initio calculations of the tensors. The calculated shift tensors for the axial and equatorial isomers of methylcyclohexane, which are also presented in this paper, are almost identical to those from the 3, 5-dimethyl-substituted compound. This indicates that chemical shift tensors for a methyl group are primarily determined by local electronic and steric factors. Changes in steric effects and/3-substituent effects between axial and equatorial methyls on the cyclohexane ring are discussed in terms of their effect upon chemical shift tensors in these paraffin hydrocarbons.