Revisiting the free energy profile for the nucleophilic attack of hydroxide on formamide in aqueous solution

The free energy profile for the first step of formamide hydrolysis in alkaline aqueous solution is computed using Car-Parrinello molecular dynamics simulation combined with umbrella sampling. An activation free energy of 22.3 kcal/mol and a reaction free energy of 17.3 kcal/mol are estimated from the potential of mean force in unprecedented good agreement with the corresponding free enthalpies obtained from experiment, 21.2 and 16.5 kcal/mol, respectively. The errors introduced by the BLYP density functional and pseudopotentials are investigated as well as the approximations made to relate the potential of mean force to the free enthalpies measured in experiment.