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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Computation of deuterium isotope perturbation of ~(13)C NMR chemical shifts of alkanes: A local mode zero-point level approach
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Computation of deuterium isotope perturbation of ~(13)C NMR chemical shifts of alkanes: A local mode zero-point level approach

机译：烷烃〜（13）C NMR化学位移的氘同位素扰动计算：局部模式零点水平方法

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摘要

Replacement of H by D perturbs the ~(13)C NMR chemical shifts of an alkane molecule. This effect is largest for the carbon to which the D is attached, diminishing rapidly with intervening bonds. The effect is sensitive to stereochemistry and is large enough to be measured reliably. A simple model based on the ground (zero point) vibrational level and treating only the C-H(D) degrees of freedom (local mode approach) is presented. The change in CH bond length with H/D substitution as well as the reduction in the range of the zero-point level probability distribution for the stretch and both bend degrees of freedom are computed. The ~(13)C NMR chemical shifts are computed with variation in these three degrees of freedom, and the results are averaged with respect to the H and D distribution functions. The resulting differences in the zero-point averaged chemical shifts are compared with experimental values of the H/D shifts for a series of cycloalkanes, norbornane, adamantane, and protoadamantane. Agreement is generally very good. The remaining differences are discussed. The proton spectrum of cyclohexane- is revisited and updated with improved agreement with experiment.
机译：用D取代H干扰烷烃分子的〜（13）C NMR化学位移。对于D所连接的碳，此作用最大，并通过中间键迅速减少。该效应对立体化学敏感，并且足够大，可以可靠地测量。提出了一个基于地面（零点）振动水平并仅处理C-H（D）自由度的简单模型（局部模式方法）。计算了使用H / D替换的CH键长度的变化，以及拉伸和两个弯曲自由度的零点水平概率分布范围的减小。通过这三个自由度的变化来计算〜（13）C NMR化学位移，并将结果相对于H和D分布函数取平均值。将零点平均化学位移的结果差异与一系列环烷烃，降冰片烷，金刚烷和原金刚烷的H / D位移的实验值进行比较。协议通常很好。其余的差异进行了讨论。对环己烷的质子谱进行了重新研究，并与实验进行了改进。

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