Photochromism and Thermochromism through Partial Torsion about an Essential Double Bond. Structure of the B Colored Isomers of Bianthrones

R. Korenstein, K. A. Muszkat*, S. Sharafy-Ozeri

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

77 Scopus citations

Abstract

The molecular structure of the colored labile B isomers of bianthrones was established by three methods: (1) proton nmr spectroscopy of the B isomers and of the lowest energy A forms in 1,1 ′-dimethylbianthrone and in the l,l′,3,3′-tetramethyl derivative; (2) minimum strain energy computation of geometries of possible metastable isomers of bianthrones formed by torsion about the 9,9′ central double bond; and (3) analysis of the remarkable low energy shift of the first electronic transition in the B isomers. We conclude that isomer B in bianthrone proper is twisted by ca. 51° about the central double bond and that each of its anthrone half-molecules is planar. In 1,1′-dimethyl-substituted molecules the corresponding twist angle is ca. 47° but the anthrone halfmolecules are significantly folded about the 9-10 axis. The observed diamagnetic shielding effects on the nmr chemical shifts of the 1-methyl protons, in both A and B forms, are in good agreement with values calculated from geometries computed by the strain energy minimalization method. The proposed structures correlate quite well with the known chemical properties of the B isomers.

Original languageEnglish
Pages (from-to)6177-6181
Number of pages5
JournalJournal of the American Chemical Society
Volume95
Issue number19
DOIs
StatePublished - 1 Sep 1973
Externally publishedYes

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