WHAT HAPPENS TO FORMAMIDE DURING C-N BOND ROTATION - ATOMIC AND MOLECULAR ENERGETICS AND MOLECULAR REACTIVITY AS A FUNCTION OF INTERNAL-ROTATION

We investigate the energetics of rotation about the C-N bond in formam ide at the molecular and atomic levels using the HF/6-31G*//HF/6-31G* level of theory. At the molecular level, the barrier to rotation res ults from a decrease in overall attractive energies upon rotation away from the planar conformation, primarily due to the lengthening of the C-N bond. At the atomic level, the barrier is due to the loss in inte ratomic attraction between the nitrogen and its bonded neighbors. We i nvestigate the susceptibility of formamide to electrophilic attack at nitrogen and oxygen as well as nucleophilic attack at carbonyl carbon as a function of C-N bond rotation using the Laplacian model of reacti vity. The model predicts the susceptibility to nucleophilic attack at carbonyl carbon to reach a maximum with a O-C-N-H torsional angle of 6 0-degrees. As a mimic of solvent fields, we investigate the effect of solvation upon these predictions with the application of homogeneous e lectric fields. This geometry-reactivity relationship is related to pr oposed models of activation in the enzymatic catalysis of peptides.