Stable Simple Enols. 9.1 Solid State Structures and Conformations of Several Simple Enols and Their Keto Tautomers

Silvio E. Biali, Zvi Rappoport, Menahem Kaftory*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

61 Scopus citations

Abstract

6, the ethanolate of 1-(9-anthryl)-2,2-dimesitylethenol (3), and trimesitylethylene (7) were determined by X-ray crystallography. The structures of 2–4 are the first ones determined for simple enols, and the structural effects of crowding on bond lengths and angles are discussed. The main features of the solid-state conformations are consistent with and reinforce those found in solution as follows: (a) Compounds 2–7 have propeller structures where all the rings are twisted from the reference plane in the same direction, corroborating static and dynamic NMR data in solution. The torsional angles of the rings in the vinyl propellers which were compared with literature values can be correlated with the rotational barriers for the enantiomerization in solution. (b) The OH group of 2 is in a syn-periplanar conformation in the direction of the cis-β-mesityl group, while that of 3 is in anti-periplanar conformation due to hydrogen bonding to an ethanol of crystallization. This is in line with the conformational dependence of the enolic OH geometry in solution on hydrogen bonding to the solvent or to the β-mesityl group. (c) The HCCO torsional angles in 5 and 6 are 177.4° and -157.8°, in agreement with the conformation suggested from UV spectra for bulky ketones in solution. (d) The a-ArCO torsional angle in 5 is 47.7°, a value lower than for formally less bulky α-aryl ketones, but in line with UV data in solution. The structures of the enols trimesitylethenol (2), (Z)-1,2-dimesityl-2-phenylethenol (4), their keto isomers 5 and.

Original languageAmerican English
Pages (from-to)1701-1709
Number of pages9
JournalJournal of the American Chemical Society
Volume107
Issue number6
DOIs
StatePublished - Mar 1985

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