An. Dixit et al., CONFORMATIONAL PREFERENCES OF ALPHA-FUNCTIONALIZED KETEN-S,N-ACETALS - POTENTIAL ROLE OF S..O AND S..S INTERACTIONS IN SOLUTION, Tetrahedron, 51(5), 1995, pp. 1437-1448
PMR spectra of carbonyl compounds 2a-k reveal significant variations i
n the population off and Z Isomers on changing the solvent from CDCl3
to DMSO-d(6). In non-polar media, the intramolecular N-H....O hydrogen
bonded form is exclusively observed. In DMSO-d(6), the alternative Z
form is also populated. A similar conformational switch is also noted
in the corresponding thiones. Different interpretations are critically
analysed. The most consistent explanation is suggested to involvean i
nterplay of N-H....X hydrogen bonding and S...X attractive interaction
(X=0,S) in these systems. Ah initio calculations support this interpr
etation.