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Stabilization of cycloalkyl carbanions in the gas phase
Author(s) -
Peerboom Renée A. L.,
Rademaker Geert Jan,
de Koning Leo J.,
Nibbering Nico M. M.
Publication year - 1992
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.1290060608
Subject(s) - carbanion , chemistry , polarizability , alkyl , medicinal chemistry , computational chemistry , organic chemistry , molecule
The gas‐phase proton affinities of five cycloalkyl carbanions and five other hydrocarbon anions have been determined by a desilylation method with use of a Fourier‐transform ion cyclotron resonance mass spectrometer. The determined proton affinites of the cycloalkyl carbonions and the electron affinities of the corresponding cycloalkyl radicals given in parenthesis are: 1708(49), 1757(−41), 1750(−38), 1750(−38) and 1739(−40)kJ mol −1 , for cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, and cycloheptyl, respectively. The results indicate that, except for the cyclopropyl carbanion, the cycloalkyl carbanions are significantly destab‐lized relative to the methyl anion. This destabilization is accounted for by the electron‐releasing effect of the alkyl groups. Furthermore, it is recognized that this destabilization is partially compensated by a stabilizing effect associated with the polarizability of the alkyl groups. Yet, this polarizability seems to be less effective in the rigid cycloalkyl carbanions than in the acyclic alkyl carbanions probably due to the anisotropic character of the polarizability effect. In contrast to its homologues, the cyclopropyl carbanion appears to be strongly stabilized relative to the methyl anion, from which it may be concluded that the alkyl electron‐releasing destabilization effect is superseded by a stabilization caused by a significant enhancement of the s‐character of the lone‐pair orbital of the carbanion which promotes the electronegativity of the atom accommadating the negative charge.