A COMPUTATIONAL STUDY OF KETO-ENOL EQUILIBRIA OF CATECHOL IN GAS AND AQUEOUS SOLUTION PHASE

Keto-enol equilibria in catechol have been studied using ab initio methods and first principle density functional theory. Six structural isomers of C6H6O2 were fully optimized in gas phase at HF and B3LYP levels of theory in combination with the 6-311++G** basis set. Self-Consistent Reaction Field Polarizable Continuum Model (SCRF-PCM) was used to investigate the effect of an aqueous solvent on the extent of tautomerisation at the two above mentioned model chemistries. In addition, gas phase electronic and Gibbs free energies for the six molecules were computed using the CBS-QB3 method, and the G3 approach to obtain highly accurate relative energies. It was found that the two dienol isomers are always lower in energy than the other species, and predominate. Resonance stabilization arising from aromaticity in these six-member cyclic systems is posited, and is understood on the basis of Hückel’s theory. In addition, it is determined that the two dienol isomers are aromatic and all the other isomers are non-aromatic by investigating Nucleus-Independent Chemical Shift (NICS) index, NICS profile, 1H-NMR chemical shift and magnetic susceptibility criteria. Confirmation of the findings is provided by comparison of the simulated vibrational spectra, structural data, and constant pressure heat capacity of catechol with experimental results. Aqueous solvent effects are fully studied using the SCRF-PCM model. Predicted infrared spectra and 1H-NMR chemical shift confirm the existence of intermolecular hydrogen bonds and intra-molecular hydrogen bonds in aqueous medium. A different approach to investigate the aqueous solvent effect by modeling catechol-(H2O)n clusters has also been initiated.

Grantor dc:publisher

Wake Forest University

Year dc:date.issued

2009

Author dc:creator

• Wang, Yuhe

• CATECHOL

Language dc:language.iso

en_US

Handle dc:identifier.uri

http://hdl.handle.net/10339/14776

OAI identifier oai:identifier

oai:wakespace.lib.wfu.edu:10339/14776