COMPUTATIONAL INVESTIGATIONS OF REACTIVE INTERMEDIATES IN THE ACID-CATALYZED PROTON-EXCHANGE IN FORMAMIDE

Ab initio calculations at various levels (up to QCISD(T) and MP4/6-311 +G(d,p)//MP2/6-31G(d)) and Monte Carlo simulations were used to invest igate protonated formamide and formimidic acid, which are presumed int ermediates in the acid-catalyzed proton exchange in formamide. Both in the gas phase and in aqueous solution, protonation at the oxygen lead s to a substantially more stable intermediate than protonation at the nitrogen. Of the two conformers of the O-protonated intermediate, one is preferred in the gas phase, but they become nearly equal in solutio n. Among the four conformers of formimidic acid, one is preferred in t he gas phase, but in solution another conformer is preferred, with two others within 1 kcal/mol. Thus, solvation plays an important role in determining relative stabilities of these intermediates.