Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
5418417 | Journal of Molecular Structure: THEOCHEM | 2006 | 8 Pages |
Abstract
We have studied the tautomerization reactions of 2,4-cyclohexadienone and 2,5-cyclohexadienone to phenol and the phenol dissociation to phenoxy radical using ab initio calculations. For the tautomerization mechanisms, the geometries were optimized at the CASSCF(8,8)/6-31G* level and the energetics were recalculated at the CASPT2(8,8)/cc-pVDZ level. For the dissociation reaction, the computational requirements for achieving comparable accuracy were stricter. In this case, the geometry optimizations were carried out at the CASSCF(10,9)/6-31G* level and the energetics were tuned with CASPT2(10,9)/aug-cc-pVTZ calculations. The tautomerization of 2,4-cyclohexadienone to phenol involved a one-step mechanism with a barrier of 53.3 kcal molâ1, while the interconversion from 2,4-cyclohexadienone to 2,5-cyclohexadienone involved a two-step mechanism, which disagreed with previous theoretical results. This interconversion occurs through a diradical intermediate. The highest barrier, between the reactant and the intermediate, was of 42.7 kcal molâ1. The best result for O-H bond dissociation enthalpy (BDE) of phenol to phenoxy was 86.2 kcal molâ1, which is within the interval proposed for this reaction by experimentalist authors. The height barrier corresponding to the rotation through the O-H bond was 3.3 kcal molâ1, which is very close to the experimental value of 3.4 kcal molâ1.
Keywords
Related Topics
Physical Sciences and Engineering
Chemistry
Physical and Theoretical Chemistry
Authors
Isabel Gómez, Elena RodrÃguez, Mar Reguero,