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The quest for a triplet ground‐state alkene: Highly twisted C═C double bonds
Author(s) -
Wu Judy I.,
Eikema Hommes Nico J.R.,
Lenoir Dieter,
Bachrach Steven M.
Publication year - 2019
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/poc.3965
Subject(s) - chemistry , alkene , singlet state , double bond , ground state , bicyclic molecule , ring strain , computational chemistry , steric effects , density functional theory , triplet state , ring (chemistry) , stereochemistry , crystallography , molecule , excited state , atomic physics , physics , organic chemistry , catalysis
Density functional theory and extrapolated CCSD(T) computations of several “anti‐Bredt” alkenes were carried to explore possible 1,2‐diyl “alkene” candidates with a triplet ground state. Ten candidates containing twisted double bonds at the bridgehead positions of bicyclic structures ( 1‐6 ) or adamantene ( 7‐10 ) derivatives were studied. Based on a combination of ring strain, rigid scaffolding, and steric crowding, four species were identified to have surprisingly low singlet‐triplet energy gaps (lower than 4 kcal/mol). A tert‐ butyl substituted bicyclic structure ( 4 ) was identified to have a near‐zero singlet‐triplet energy gap, but no triplet ground‐state alkene was found. Ring strain energy (RSE) calculations, π‐orbital axis vector (POAV) analyses, and multiple linear regression models were performed to elucidate the geometric and energetic effects of double bond twisting in 1‐10 . Based on our computational exploration, it appears unlikely that there is a ground‐state triplet olefin.