Nematic phase nuclear magnetic resonance, ultrasonic relaxation, and theoretical ab initio investigation of internal rotation in pyridine-2-carbaldehyde

Abstract

The 100 MHz ¹H n.m.r. spectrum of pyridine-2-carbaldehyde partially oriented in the nematic phase of a liquid crystalline solvent has been obtained and analysed. It has been shown that a conformational equilibrium is present and that theN–O-trans-form is the more stable (ca. 96%). The barrier height to cis–trans-interconversion in the pure liquid has been investigated by means of the ultrasonic relaxation technique and a value of 4.5 ± 0.3 kcal mol^–1 has been found. The hindering internal potential has also been investigated by means of quantum mechanical calculations using the SCF–MO–LCAO ab initio method. The overall results have been compared with previous experimental findings and theoretical calculations.