Dual substituent parameter analysis of the ethyl and ipso13C n.m.r. chemical shifts of some ring‐substituted ethylbenzenes and ethylnaphthalenes

Abstract The natural abundance 13C n.m.r. spectra of a series of para‐substituted ethylbenzenes, 4‐substituted‐1‐ethylnaphthalenes and a limited series of 6‐substituted‐2‐ethylnaphthalenes have been examined at low dilution in deuterochloroform solvent. The ethyl carbons and Cipso in the phenyl series (i.e. have been assigned, and substituent chemical shifts for these carbons calculated and analysed by the Dual Substituent Parameter treatment. (Chemical shifts of all ring carbons have been obtained, but not assigned). Generally speaking, electron‐withdrawing substituents lead to positive (i.e. downfield) substituent chemical shifts for CH2 and negative substituent chemical shifts for CH3, i.e. ‘normal’ and ‘inverse’ behaviour respectively. Cipso in the phenyl series exhibits a ‘normal’ dependence. The dependences of the various substituent chemical shifts on inductive and resonance parameters are discussed, and compared with the behaviour of side chain carbons in other substituted benzene systems.