Experimental and theoretical study of the methoxy group conformational effect on ¹³C chemical shifts in <i>ortho</i>‐substituted anisoles

Abstract

Abstract Aromatic 13 C chemical shifts are reported for a number of ortho ‐substituted anisoles. Quantitative determination of the substituent chemical shift (SCS) effects of the methoxy group with a fixed coplanar conformation on aryl carbon nuclei was achieved using experimental and theoretical methods. The experimental values were compared with those calculated through the use of the additivity, and a systematic departure from additivity was found for carbon nuclei in ortho positions. Ortho ‐SCSs were found to be non‐equivalent, and the ortho effect on the carbon cis to the fixed methoxy moiety was more shielding than in anisole. The IGLO (Individual Gauge for Localized Orbitals) method was used to calculate the SCSs. Experimental and theoretical trends obtained for the influence of the side‐chain conformations on chemical shifts are in very good agreement with each other, and with recent results obtained by solid‐state NMR.