A quantum mechanical study of the equilibrium between 1,4- and 1,6-dialkylcyclooctatetraenes

✍ Scribed by Camillo Tosi

• Publisher: John Wiley and Sons
• Year: 1984
• Tongue: English
• Weight: 375 KB
• Volume: 5
• Category: Article
• ISSN: 0192-8651
• DOI: 10.1002/jcc.540050307

✦ Synopsis

The equilibrium between three pairs of 1,4-and 1,6-dialkylcyclooctatetraenes was investigated with the two quantum mechanical algorithms, IBMOL and PCILO. PCILO computations reproduce the trend of stability within each pair of isomers obtained earlier by Allinger with molecular mechanics calculations, while IBMOL computations do not. These results not only can be explained in the light of, but also are a confirmation of Allinger's conclusions that the conformational stability is governed by the magnitude of the van der Waals' attraction between the two alkyl groups: The dispersion energy, which is essentially an electron correlation effect, is not accounted for by a method like IBMOL that, albeit ab inzti0, is based on the Hartree-Fock independent particle model, while it is fairly well reproduced by a method like PCILO that, albeit semiempirical, is based on a configuration interaction approach. Simulation of the full configuration interaction (CI) correction through a suitable dispersion term brings IBMOL results to a good agreement with the molecular mechanics ones.