Tautomerization is a fundamental chemical phenomenon with applications in synthetic organic chemistry and biochemistry. The current work benchmarks multiple DFT methods, i.e., B3LYP, X3LYP, M05, M05-2X, M06, M06-2X, ?B97XD, HSE06, and PBEh1PBE in combination with nine basis sets up to 6-311++G(3df,3pd) and aug-cc-pVTZ to reproduce seven gas phase experimental free energies of tautomerization (?Gtaut). The most accurate method in vacuum, M06/6-31+G(d,p), with a mean unsigned error of 0.88 kcal/mol, was used to benchmark the IEFPCM, CPCM, and SMD implicit solvation models, in conjunction with the Bondi, Pauling, UA0, UAHF, UAKS, and UFF cavities, against 50 condensed-phase experimental ?Gtaut. The classes of tautomerizations explored were keto-enol, keto-iminol, and thioketone-thiol. Intriguingly, a solvent-dependent rate enhancement and change in isomer preference for the keto-enol tautomerization of alicyclic a-nitroketones has been observed experimentally. The mechanism of the base-catalyzed enolization of 2-nitrocyclohexane has been investigated using DFT/PCM and QM/MM methodologies in solvents of varying polarity.

Benchmarking tautomerization reactions using continuum solvation models

244th National Meeting (2012)

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