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Correlation of singlet‐triplet gaps for aryl carbenes calculated by MINDO/3, MNDO, AM1, and PM3 with Hammett‐type substituent constants
Author(s) -
Karaman Rafik,
Huang JunTsu Luke,
Fry James L.
Publication year - 1991
Publication title -
journal of computational chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.907
H-Index - 188
eISSN - 1096-987X
pISSN - 0192-8651
DOI - 10.1002/jcc.540120503
Subject(s) - mindo , mndo , singlet state , chemistry , substituent , computational chemistry , standard enthalpy of formation , aryl , homo/lumo , diradical , photochemistry , molecule , atomic physics , stereochemistry , physics , organic chemistry , alkyl , excited state
Heats of formation, atomic charges, and geometries of some 110 structures involving substituted singlet and triplet phenyl and 4,4‐dimethyl‐1,4‐dihydronaphthalene carbenes and the corresponding diazomethanes were calculated by MINDO/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 σ + constants. Good correlations with σ + 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.