Equilibrium constants for enolization in solution by computation alone1. (12th July 2013)

• Record Type: Journal Article
• Authors: Guthrie, J. Peter; Povar, Igor; Page, Michael I.
• Is Part Of: Journal of physical organic chemistry. Volume 26:Number 12(2013:Dec.)
• Page Start: 1077
• Page End: 1083
• Publication Date: 2013-07-12
• Subjects: Chemistry, Physical organic -- Periodicals; 547.1
• DOI: 10.1002/poc.3168
• Languages: English
• ISSNs: 0894-3230

Abstract

<abstract abstract-type="main"> <title> <x xml:space="preserve">Abstract</x> </title> <p>Equilibrium free energy changes for <named-content id="d190e1127" content-type="reactionType" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink">enolization</named-content> 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 <named-content id="d190e1130" content-type="reactionType" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink">enolization</named-content> 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 <named-content id="d190e1133" content-type="reactionType" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink">enolization</named-content> equilibria of 1, 3, 5‐cyclohexanetrione (phloroglucinol); we argue that the problems are with the experimental values. Reasonable values are obtained for the <named-content id="d190e1143" content-type="reactionType" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink">enolization</named-content> 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. Copyright © 2013 John Wiley & Sons, Ltd.</p> </abstract>