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Comparison of differentab initio theoretical models for calculating isodesmic reaction energies for small ring and related compounds

1997; Wiley; Volume: 18; Issue: 1 Linguagem: Inglês

10.1002/(sici)1096-987x(19970115)18

1096-987X

Kenneth B. Wiberg, Joseph W. Ochterski,

Molecular Junctions and Nanostructures

Isodesmic reactions are commonly used in ab initio studies to partially cancel errors associated with incomplete basis sets and incomplete correction for electron correlation. The errors associated with these reactions have been examined using the 6–31G* basis set at the theoretical levels HF, MP2, MP3, MP4, and B3LYP, and using the 6–311 + G* basis set at the HF, MP2, and B3LYP levels. As a comparison, the recently developed model chemistries, CBS-4 and CBS-Q, were also used. With hydrogenation and hydrogenolysis reactions, only the HF level gave large deviations from the experimental reaction energies. The use of hydrogen transfer reactions improved the HF calculated energies, but mixed results were obtained at the correlated levels. Some isomerization reactions and reactions of carbocations also were examined. The MP4/6–31G* and CBS-Q levels of theory were uniformly the more satisfactory. © 1997 by John Wiley & Sons, Inc.