TY - JOUR
T1 - Stable Simple Enols. 9.1 Solid State Structures and Conformations of Several Simple Enols and Their Keto Tautomers
AU - Biali, Silvio E.
AU - Rappoport, Zvi
AU - Kaftory, Menahem
PY - 1985/3
Y1 - 1985/3
N2 - 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.
AB - 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.
UR - http://www.scopus.com/inward/record.url?scp=0000733416&partnerID=8YFLogxK
U2 - 10.1021/ja00292a041
DO - 10.1021/ja00292a041
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AN - SCOPUS:0000733416
SN - 0002-7863
VL - 107
SP - 1701
EP - 1709
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
IS - 6
ER -