Conformational structures and dynamics of cis-n-alkenyl amides

Parallel experimental and computational studies of phenyl cis- and trans-n-alkenyl amides (tuberines) have been carried out to probe the structural and dynamic properties with particular attention to interaction between the conjugated enamides chain and the aromatic ring. The cis isomers are non-planar with 40–508 due to steric interactions between the enamide chain and aromatic ring,whereas the trans form is essentially planar. Rotation barriers for the carbonyl group about the C–N bond are predicted to be 18–22 kcal/mol at HF, B3LYP, and MP2 levels using the cc-pVDZ basis set. Despite its significant non-planarity,the cis conformation of tuberine is not found to be significantly less stable than the trans conformation. q 2003 Elsevier B.V. All rights reserved.