13C nuclear magnetic resonance studies on aromatic aldehydes. Torsional barriers and conformational equilibria in pyridinecarbaldehydes

Abstract

Low temperature ¹³C n.m.r. has been used to study the barrier to internal rotation and the NO-cis : NO-trans population ratio in the three pyridinecarbaldehydes. The total bandshape analysis method was utilized, which resulted in trans-populations for pyridine-2- and -3-carbaldehyde of 0.94 and 0.80, respectively, a: –123°. The results are compared with previous data obtained by other methods.