Azolides. VII—Restricted rotation in N ‐acylindoles and carbazoles. Anisotropy effect of the carbonyl group

The barrier to internal rotation about the NC bond and the E/Z configuration of some N ‐acetyl and N ‐formylindole derivatives have been determined and discussed in terms of electronic and steric effects. The barriers to internal rotation have been determined for certain N ‐acetylcarbazoles and some new N ‐formyl derivatives of carbazole. Experimental proof is also given, showing that contrary to the provisions of the classical model of carbonyl anisotropy, the protons (α and peri positions) next to the oxygen of the acyl group are displaced to high frequencies. This result allows one to determine the preferred configuration of N ‐acetyl derivatives of perimidine and 1H‐naphtho[1,8‐de]triazine.