Ab Initio Study of the Internal Rotation Barrier of Formamide and the Formamide-H2O Complex. (Reannouncement with New Availability Information)

摘要

The barriers to internal rotation about the N-C bond of formamide and theformanide-H2O complex have been examined by ab initio quantum chemistry methods. Both selfconsistent field and correlated approaches have been utilized to determine the geometries, energies, and local harmonic vibrational frequencies of the minimum-energy and transitionstate structures of these two systems. We find that formamide's rotation barrier of 14-15 kcal/mol is increased to 16-18 kcal/mol when a single H2O molecule is attached. This result contrasts with the effect of a single H2O solvent molecule on the barrier to tautomerization of formamide (to form formamidic acid HN-CHOH) for which a barrier lowering of ca. 20 kcal/mol has been observed. The rotation barriers obtained for formamide and for its H2O complex are compared with barriers obtained experimentally in various systems.