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Density functional calculations of the influence of substitution on singlet–triplet gaps in carbenes and vinylidenes
Author(s) -
Worthington Sharon E.,
Cramer Chistopher J.
Publication year - 1997
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/(sici)1099-1395(199710)10:10<755::aid-poc935>3.0.co;2-p
Subject(s) - chemistry , hyperconjugation , carbene , singlet state , computational chemistry , density functional theory , natural bond orbital , redistribution (election) , inductive effect , multiplet , halogen , atomic physics , excited state , molecule , organic chemistry , quantum mechanics , catalysis , physics , alkyl , politics , political science , law , spectral line
NDensity functional theory calculations of multiplet splittings are presented that agree closely with experimental measurements for six carbenes and six vinylidenes. The calculations are further analyzed to gauge the relative importance of different factors influencing the stabilities of the different spin and electronic states. In the carbene series, with halogen substituents, orbital rehybridization effects and charge redistribution effects are large. The magnitude of π‐conjugation (back‐bonding) is calculated to be only moderately larger (6–8 kcal mol −1 ) for singlets than for triplets based on natural bond orbital‐derived conjugation energies. In the vinylidene series, substituion effects are primarily associated with through‐space and through‐bond inductive stabilization effects, especially hyperconjugation; π‐conjugation effects are found to be small © 1997 John Wiley & Sons, Ltd.