2-酰基-1,3-环二酮类化合物互变异构的理论计算

采用MP2/6-31+G**//B3LYP/6-31+G**方法,系统地研究了2-酰基-1,3-环二酮类化合物的互变异构性质,探讨了环的饱和性、环的大小、环上杂原子以及溶剂效应对各互变异构体相对稳定性的影响。结果表明:(1)未烯醇化的异构体由于无法形成分子内氢键而具有较高的能量;(2)环上杂原子的推电子效应提高了邻位羰基氧上的负电荷,从而有利于相应环外烯醇式异构体的稳定;(3)对化合物3-酰基-1H-吡啶-2,4-二酮,3-酰基吡喃-2,4-二酮,2-酰基环戊-4-烯-1,3-二酮和3-酰基吡咯-2,4-二酮,由互变异构形成的环的芳香性在各异构体的相对稳定性中扮演着决定性的作用。

Theoretical Calculations on the Tautomerisms of 2-Acetyl-cyclo-1,3-dione Compounds

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.