The N-phenylformamide biomolecule has been investigated by ab initio calculations in order to study the conformational flexibility and the relative energy between the E and Z conformers. By following a systematic methodology, the MP2/VTZ level of the theory was found to provide accurate molecular parameters. The controversy on the relative energy value has been theoretically and experimentally resolved. (c) 2005 Elsevier B.V. All rights reserved.