Abstract13C and17O NMR data [chemical shifts and1J(CH) values] for the methoxy groups in isomeric 1,2‐, 1,3‐ and 1,4‐dimethoxybenzenes, 1,2,3‐trimethoxybenzenes and most of their chlorinated derivatives and some related brominated compounds were measured for CDCl3solutions. The17O NMR chemical shifts show up to 60 ppm dispersion. Comparison between the compounds with and without adjacent chlorine atoms (2,6‐di‐ and 2,4,6‐tri‐substitution) also showed a clear methoxy carbon chemical shift change. The number and position of the chlorine atoms in the aromatic ring give small but observable effects on the17O NMR chemical shifts of the methoxy group if it is coplanar with the aromatic plane. Similarly, the degree and nature of the substitution have a minor effect (about 1 Hz) on the1J(CH) direct