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Rigorous interpretation of electronic wavefunctions. IV. Origins of the unusual stability of the 1,3‐dimethylimidazol‐2‐ylidene carbene
Author(s) -
Cioslowski Jerzy
Publication year - 1993
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.560480832
Subject(s) - carbene , wave function , chemistry , electronic structure , ab initio , computational chemistry , stability (learning theory) , ab initio quantum chemistry methods , interpretation (philosophy) , atomic physics , physics , molecule , organic chemistry , catalysis , machine learning , computer science , programming language
Ab initio electronic structure calculations, carried out in conjunction with rigorous analysis of the resulting wavefunctions, demonstrate that the electronic factors responsible for the unusual stability of the 1,3‐dimethylimidazol‐2‐ylidene carbene are directly related to the substantial σ‐backdonation from the carbenic carbon to the adjacent nitrogen atoms. The π‐donation is found to play only a minor role, ruling out the presence of significant stabilization due to ylidic resonance structures. The unusually large proton affinity of the carbene is explained by the extra π‐electron stabilization of the corresponding 1,3‐dimethylimidazolium cation. The MP2/6‐311++G** level of theory is found to be sufficient for accurate predictions of the geometries of the imidazol‐2‐ylidene carbenes. © 1993 John Wiley & Sons, Inc.