Quantum-chemical study of molecular structure and relative stability of trans and cis isomers of model anilide derivatives

Derivatives of anilide were studied systematically by the density functional theory (DFT) using the B3LYP hybrid functional and the 6-311+G(3df,2p) basis set. Characteristic frequencies of N-H and C=O stretching modes for cis and trans conformers distinguishing were compared with available experimental and theoretical data. Effect of substitution in ortho position and acidic residue group is discussed with respect to the bond length changes in the aromatic ring and aromaticity indexes. Energy differences between cis and trans conformations allow estimating the effect of intramolecular hydrogen bonds stabilizing the studied conformations. The trans conformation of parent formanilide is stabilized via the C_(aromatic) -H∙∙∙O=C interaction with the energy of around 4 kJ・mol^-1. The selected anilide series represent model compounds for drug design.