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Reliable Reaction Enthalpies for Neutral Amide Hydrolysis and the Heat of Formation for Formamide

1996; American Chemical Society; Volume: 100; Issue: 10 Linguagem: Inglês

10.1021/jp952677s

1541-5740

Kerwin D. Dobbs, David A. Dixon,

Molecular Junctions and Nanostructures

High level ab initio electronic structure calculations have been done for the hydrolysis reaction X2NC(O)Y + H2O → X2NH + HOC(O)Y for X = Y = H (formamide) and for X = H and Y = CH3 (acetamide). Calculations are reported with a variety of basis sets and a variety of correlation levels based on molecular orbital (MO) theory as well as with a variety of density functional theory (DFT) gradient-corrected (nonlocal) functionals. The convergence of the hydrolysis energies with respect to the computational method is discussed. The highest level calculations yield 0.3 ± 0.4 and 0.1 ± 0.4 kcal/mol at the MO and DFT levels, respectively, for X = H and Y = CH3 as compared to an experimental value of 0.4 ± 0.9 kcal/mol. For X = Y = H, the hydrolysis energies are 1.7 ± 0.4 (MO) and 2.2 ± 0.4 (DFT) kcal/mol. The heat of formation of formamide was calculated from the isodesmic reaction H2NC(O)CH3 + HOC(O)H → H2NC(O)H + HOC(O)CH3, giving ΔH°f = −45.6 ± 1.1 (MO) and −46.2 ± 1.1 (DFT) kcal/mol. These values for ΔH°f (formamide) yield 1.9 ± 1.3 (MO) and 2.5 ± 1.3 (DFT) kcal/mol for the hydrolysis reaction.