REACTION PATHWAYS FOR PROTON-EXCHANGE BETWEEN PROTONATED FORMAMIDE AND WATER

Ab initio molecular orbital calculations at the RHF/6-31 + G(d) and MP 2/6-31 + G(d) level were utilized to explore proton exchange pathways between protonated formamide and water. Three different pathways were found. Two were similar to each other, differing only in the conformat ion of O-protonated formamide that serves as the starting point. In th ese pathways, and NH proton was transferred to water, forming an imidi c acid-hydronium ion complex as the transition state, followed by back transfer of a different proton leading back to O-protonated formamide and water. In the third pathway, an OH proton of O-protonated formami de was transferred to water, forming a formamide-hydronium ion complex as the transition state. Back transfer of the proton was to the amide nitrogen, leading to N-protonated formamide and water. The torsional profile of the C-N bond in the complex between N-protonated formamide and water was also explored. It was found that rotation around this bo nd was accompanied by a rotation of the water molecule with twice the period. (C) 1998 Elsevier Science B.V.