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An ab initio study of the geometry and energy of six planar conformers of β-hydroxyacrolein

✍ Scribed by Phillip George; Charles W. Bock; Mendel Trachtman

Publisher
John Wiley and Sons
Year
1980
Tongue
English
Weight
853 KB
Volume
1
Category
Article
ISSN
0192-8651

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✦ Synopsis

Abstract

Ab initio calculations with full geometry optimization have been carried out on the planar cCc, cTc, tTc, tCt, tTt, and cCt conformers of β‐hydroxyacrolein using the 4‐21G basis set, and on the cCc and cCt conformers using the 4‐31G basis set. The hydrogen‐bonded cCc conformer is the most stable and the cCt conformer the least stable, with the other conformers following the above sequence. β‐Hydroxy substitution has scarcely any influence on the geometry of the trans‐acrolein structure, whereas the geometry of the cis‐acrolein structure shows significant changes which depend on whether the OH group is cis or trans with respect to the CHO group about the CC bond. The Δ__E__~T~ values for cis → trans isomerization about the CC bond in cCt and cTc support the hypothesis that these changes in geometry are the result of a destabilizing interaction in cCt and a stabilizing interaction in cTc. The geometry of the hydrogen‐bonded structure cCc sets it apart from all the other conformers: it has by far the longest CC, the longest CO, the longest OH, the shortest CC, and the shortest CO. Its formation from cCt involves a lengthening of CC, CO, and OH and a shortening of CC and CO, indicating a delocalization of charge within the ring. 4‐21G calculations have also been made for a distorted cCt structure that has the same bond lengths and angles as the equilibrium cCc structure, and the distortion energy, cCt (equm. geom.) → cCt (distorted geom.), is found to be +13.1 kJ mole^−1^. Taking the energy of this distorted cCt structure as the baseline, the hydrogen‐bonding energy in cCc is found to be —80.3 kJ mole^−1^.

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