AbstractChemical shifts and substituent chemical shift (SCS) effects are reported for 21 monosubstituted iso‐quinolines, carrying a halogeno, amino, piperidino or ethoxy group in position 1, 3 or 4. In some cases, assignments of13C resonances were based on the spectra of the corresponding 5‐deutero derivatives. For the fluoroisoquinolines some13CF coupling constants are given. The13C NMR spectra of 15 disubstituted isoquinolines were measured; with a few exceptions, mainly the 3,4‐ and 1,4‐disubstituted isoquinolines, the chemical shifts agreed well with those calculated by addition of the SCS