Substituent effects on the zero-field splitting parameters of diarylmethylene. Evidence for merostabilization in appropriately substituted diphenylmethylenes
Open Access
- 1 October 1979
- journal article
- Published by Canadian Science Publishing in Canadian Journal of Chemistry
- Vol. 57 (19) , 2652-2661
- https://doi.org/10.1139/v79-430
Abstract
An analysis of the temperature dependence (4–30 K) of the electron spin resonance (esr) spectra of substituted diphenylmethylenes (e.g. para-, para′-; methoxy, cyano, dimethylamino, and nitro) indicates all of these species have a triplet ground state. The variation in the zero-field splitting parameter D for this series of methylenes provides evidence that the average separation of the unpaired electrons is greatest for the unsymmetrically substituted derivatives, those having a strong para-electron-withdrawing substituent and a strong para′-electron-donating substituent. This result is explained in terms of a favourable contribution of charge-separated valence-bond structures, i.e., merostabilization.Keywords
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