Conformational Structures and Dynamics of cis-n-Alkenyl Amides

Conformational Structures and Dynamics of cis-N-Alkenyl Amides

Lucina Guadalupe Sanchez Martir, Gerardo Aguirre Hernandez, A. L. Cooksy, Lars Helberg, Ratnasamy Somanathan, and Felipe Ramirez Romero

Centro de Graduados e Investigacion del Instituto Tecnologico de Tijuana, Apdo Postal 1166, Tijuana, B.C. Mexico
and
Department of Chemistry, San Diego State University, San Diego CA 92182-1030

Abstract

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--50 degrees 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.