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Equilibrium constants for enolization in solution by computation alone

Domenii publicaţii > Chimie + Tipuri publicaţii > Articol în revistã ştiinţificã

Autori: Guthrie J.P., Povar I.

Editorial: NRC Research Press, J. Phys. Org. Chem. , 87(8), p.1154-1162, 2013.


Equilibrium free energy changes for enolization in aqueous solution can be calculated with useful accuracy (rmse = 1.3 kcal/mol for 37 reactions). These calculations involve gas phase free energy changes calculated using the G3MP2B3 method and solvation energies calculated using the IPCM method corrected by a parameterization scheme which we have reported. For chloroacetones, we find a small preference for enolization to the halogenated side and a preference for forming an enol with Cl Z to the OH. This may be partly due to weak hydrogen bonding but must be partly due to a relief of crowding; 2-butanone also shows a preference for the Z-enol. There are serious disagreements between calculated and experimental values for some of the enolization equilibria of 1,3,5-cyclohexanetrione (phloroglucinol); we argue that the problems are with the experimental values. Reasonable values are obtained for the enolization of Meldrum’s acid, diethyl malonate, and 1,3-cyclohexanedione. Computational equilibrium constants in aqueous solution are now viable as supplements to and checks on experiment.

Cuvinte cheie: enolizare, constante de echilibru, calculele orbitalelor moleculare, solvatare // enolization, equilibrium constant, molecular orbital calculations, solvation