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

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.