Conformational studies by dynamic nuclear magnetic resonance. Part 13. Torsional barriers and conformational analysis of N-acylcarbazoles

Abstract

The ¹³C n.m.r. spectra of N-acylcarbazoles at low temperature (between –5 and –140 °C) display non-equivalence of the aromatic carbons owing to restricted rotation about the N–COR bond. The free energies of activation were measured and the differences between the various substituents interpreted as due to steric effects in the alkyl, and to electronic properties in the aryl derivatives. A quantitative lanthanide-induced shift (LIS) investigation allowed a measure of the angle between the plane of the RCO group and the aromatic ring for R = Me (25°) and R = Bu^t(75°).