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Tetrasubstituted bisadamantylidenes—Highly twisted alkenes
Author(s) -
Bachrach Steven M.
Publication year - 2018
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.3840
Subject(s) - chemistry , isomerization , steric effects , singlet state , basis set , photochemistry , electron paramagnetic resonance , double bond , nuclear magnetic resonance spectroscopy , computational chemistry , stereochemistry , density functional theory , catalysis , organic chemistry , nuclear magnetic resonance , atomic physics , physics , excited state
A number of 1,3,1′,3′‐tetrasubstituted bisadamantylidenes are examined with 4 different density functional methods (BP86‐D3, ωB97X‐D, B3LYP, and B3LYP‐D3) and the 6‐311G(d) basis set. With increasing steric bulk, these substituted bisadamantylidenes become ever more twisted about the central carbon‐carbon double bond. This manifests in significantly reduced singlet‐triplet gaps from that of typical alkenes, with the tetra‐ t‐ butylbisadamantylidene 17 , twisted to almost 90°, having a gap of only 2.2 kcal mol −1 . While its large strain energy may preclude the synthesis of 17 , other less‐strained tetrasubstituted analogues are more feasible synthetic targets and still possess small singlet‐triplet gaps, which should be testable by variable temperature NMR and EPR spectroscopy. The twisted alkenes also result in a low rotational energy barrier, and 4 examples with a low barrier to cis‐trans isomerization are presented. These too should be testable by experiment.