期刊
JOURNAL OF PHYSICAL CHEMISTRY A
卷 114, 期 46, 页码 12283-12290出版社
AMER CHEMICAL SOC
DOI: 10.1021/jp105913x
关键词
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资金
- NSF [CHE0848790]
- iREU [NSF CHE075538]
- Direct For Mathematical & Physical Scien
- Division Of Chemistry [0848790] Funding Source: National Science Foundation
Replacement of H by D perturbs the C-13 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 C-13 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.
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