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meta and para substitution effects on the electronic state energies and ring‐expansion reactivities of phenylnitrenes
Author(s) -
Johnson William T. G.,
Sullivan Michael B.,
Cramer Christopher J.
Publication year - 2001
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.1518
Subject(s) - intersystem crossing , chemistry , singlet state , density functional theory , perturbation theory (quantum mechanics) , computational chemistry , ring (chemistry) , excited state , substitution (logic) , spin–orbit interaction , configuration interaction , ground state , triplet state , electronic structure , atomic physics , physics , quantum mechanics , organic chemistry , computer science , programming language
The electronic structures of the triplet ground states and first three excited singlet states for phenylnitrene, 14 meta ‐, and 17 para ‐substituted congeners have been characterized using density functional theory and multireference second‐order perturbation theory (CASPT2). Ring expansion pathways to form didehydroazepines have activation enthalpies of about 9 kcal⋅mol −1 and are fairly insensitive to substitution—in the case of the strongest para donor, MeNH–, this barrier increases to about 13 kcal⋅mol −1 . The trends in state energies as a function of substitution are rationalized using a (2,2) configuration interaction theory and qualitative molecular orbital theory. Analysis of spin‐orbit coupling in the nitrenes using the same model in conjunction with explicit calculation of spin‐orbit coupling matrix elements rationalizes why electron donating substituents increase rates of intersystem crossing. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001