The Linearity of the Substituent-induced Carbon-13 Chemical Shifts of α-Carbons with Charge Densities in Aromatic Side Chains. Semi-empirical Calculations for 4-Substituted Derivatives of Styrenes, α-Methylstyrenes, and Biphenyls

Abstract

Abstract The contributions to 13C shifts from the diamagnetic term of the neighboring carbon atom and from the “ring-current” have been estimated by means of the equations given in a previous paper (J. Niwa, Bull. Chem. Soc. Jpn., 48, 118 (1975)). A semi-empirical expression has been derived for the substituent-induced 13C chemical shift in an aromatic side chain by considering such contributions in addition to the local diamagnetic and paramagnetic terms of the carbon atom in question. The applicability of the expression has been examined for α-carbons of 4-substituted derivatives of styrenes and α-methylstyrenes, and for 1′-carbons of 4-substituted biphenyls.