Singlet benzyne thermochemistry: a CASPT2 study of the enthalpies of formation

✍ Scribed by Roland Lindh; Martin Schütz

• Publisher: Elsevier Science
• Year: 1996
• Tongue: English
• Weight: 543 KB
• Volume: 258
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(96)00653-7

✦ Synopsis

The enthalpies of formation for singlet benzynes were examined at the CASPT2 (second order perturbation theory, based on a complete active space SCF reference function) level of theory. The study employed isodesmic reactions in order to minimize the influence of systematic errors of the method. The results obtained for m-and p-benzyne were found to dispute earlier experimentally deduced values; a discrepancy of about 5 kcal/mol was observed. As a consequence, the enthalpy of reaction of the so called Bergman reaction, deduced previously from the experimental enthalpy of formation of p-benzyne, seems to be overestimated by about 5 kcal/mol. Furthermore, it was observed that the CCSD(T) method (coupled cluster singles and doubles with a perturbatative estimate of the triples contribution) is inappropriate for a balanced treatment of the Bergman reaction, due to the extensive differences in the electronic structures of the two reactants.