The Correlation of 13C Chemical Shifts of Steroids with Atomic Charges Calculated by the Extended Hückel Molecular Orbital Method

Abstract

13C chemical shifts of several of the sterols and steroidal hormones which have been investigated by Reich et al. (J. Amer. Chem. Soc. 91, 7445 [1969]) are compared with the atomic charges derived from extended Hückel molecular orbital calculations for these molecules. The linear regression analysis of 126 observations for aliphatic carbons gives a correlation coefficient of 0.81, and a standard error of estimate of 8.2 ppm. The largest discrepancies arise for carbons in the neighbourhood of methyl groups, which cannot be attributed to deficiencies of the extended Hückel theory. The corrections for carbons in the α, β, and γ positions to a methyl group amount to + 11.75, - 6.44, and +4.45 ppm, respectively. The results are discussed in relation to the structural analysis of steroids.