Correlation of singlet-triplet gaps for aryl carbenes calculated by MINDO/3, MNDO, AM1, and PM3 with Hammett-type substituent constants

✍ Scribed by Rafik Karaman; Jun-Tsu Luke Huang; James L. Fry

• Publisher: John Wiley and Sons
• Year: 1991
• Tongue: English
• Weight: 981 KB
• Volume: 12
• Category: Article
• ISSN: 0192-8651
• DOI: 10.1002/jcc.540120503

✦ Synopsis

Heats of formation, atomic charges, and geometries of some 110 structures involving substituted singlet and triplet phenyl and 4,4-dimethyl-l,4-dihydronaphthalene carbenes and the corresponding diazomethanes were calculated by MIND0/3, MNDO, AM1, and PM3 semiempirical molecular orbital methods. The singlet-triplet gaps for AM1 and PM3 calculations for the para derivatives in both systems have been successfully correlated with Brown o+ constants. Good correlations with o+ were found for the charges on the carbenic centers of the singlets as well as with the energy barrier for rotation of the aryl group about the C-C single bond in substituted singlet phenylcarbenes. Comparisons of these results with experimental data indicate that AM1 and PM3 are much better than MNDO and MINDO/3 in predicting the intrinsic substituent effects in singlet carbenes.