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Ultraviolet Absorption Spectrum of Malonaldehyde in Water Is Dominated by Solvent-Stabilized Conformations.

Authors
  • Xu, Xuefei
  • Zheng, Jingjing
  • Truhlar, Donald G
Type
Published Article
Journal
Journal of the American Chemical Society
Publisher
American Chemical Society
Publication Date
Jul 01, 2015
Volume
137
Issue
25
Pages
8026–8029
Identifiers
DOI: 10.1021/jacs.5b04845
PMID: 26081988
Source
Medline
License
Unknown

Abstract

Free energy calculations for eight enol isomers of malonaldehyde (MA) and simulation of the ultraviolet (UV) absorption spectrum in both the gas phase and water (pH = 3, where the molecule exists in neutral undeprotonated form) show that in water the two s-trans nonchelated enol conformers of MA become thermodynamically more stable than the internally hydrogen-bonded ("chelated enol") conformer (CE). The pure CE conformer in water has a slightly red-shifted UV spectrum with respect to that in the gas phase, but the blue-shifted spectrum observed in water at pH 3 is dominated by solvent-stabilized conformations that have negligible populations in the gas phase. Density functional calculations with the solvation model based on density (SMD) and an ensemble-averaged vertical excitation model explain the experimental observations in detail.

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