Wang Yan
2004
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Journal
Chinese Journal of Structural Chemistry
Abstract
In this paper, tautomerisms of a series of 2-acetyl-cyclo-1,3-dione compounds have been investigated at the MP2/6-31+G**//B3LYP/6-31+G** level. The influence on saturation degree of rings, ring size, hetero- atoms in the ring and polarity of solvent on the relative stability of the tautomers was studied. It is demon- strated that: (1) unenoliazted isomers have high energy due to the absence of intramolecular hydrogen bonds; (2) the negative charges on carbonyl oxygen are increased because of the electron-donating effect of the heteroatom in the ring, which is in favor of the stability of the corresponding exocyclic enoltautomer; and (3) for compounds 3-acetyl-1H-pyridine-2,4-dione, 2-acetylpyran-2,4-dione, 2-acetylcyclopent-4-ene-1,3-dione and 2-acetyl-pyrrole-2,4-dione, the aromaticity of rings plays a crucial role in the relative stability of the isomers.