CNDO/2 Study of Polar Interactions in Acetonitrile

The interaction of two acetonitrile molecules has been studied by the CNDO/2 approximation of the MO method. The antiparallel dipoles model obtains a 4.5 kcal/mole energy gain at a contact distance of 2.35 A. The skewed‐T interaction configuration gives an energy gain about ten times larger at a much shorter contact distance, 1.6 A. This latter model seems however much more affected than the other by the shortcomings of the CNDO/2 approximation. The reported calculations indicate the skewed‐T interaction to be stronger than that of two antiparallel molecules, and suggest the possible presence of polymeric clusters in the liquid. Both interaction models evolve towards the formation of a (CN) 2 unsaturated ring, which in turn might go into a more stable nearly‐tetrahedral cage structure.