Low-Temperature 13C Magnetic Resonance. 9. Steric Effects for Methyl Chemical Shift Tensors in Methylcyclohexanes

The solid-state low-temperature ¹³C NMR spectra of 1-(methyl-¹³C)-1-methylcyclohexane, cis-1-(methyl-¹³C)-3,5-dimethylcyclohexane, and trans-1-(methyl-¹³C)-3,5-dimethylcyclohexane 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 β-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. © 1995, American Chemical Society. All rights reserved.

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Author Julio Cesar Facelli Biostatistics & Bioinformatics, Division of Translational Bi ...