Department of Chemistry, University of Technology and Life Sciences, Seminaryjna 3, 85-326 Bydgoszcz, Poland.
J Mol Model. 2013 Aug;19(8):3397-402. doi: 10.1007/s00894-013-1874-0. Epub 2013 May 18.
Density functional theory (DFT) calculations at the B3LYP/6-311+G(d,p) level show that 4,6-di(pyridin-2-yl)cyclohexane-1,3-dione is a labile compound. On the other hand, its dienolimine tautomer (4,6-di(pyridin-2-yl)cyclohaxa-1,3-diene-1,3-diol) seems stable enough to be present in vacuum. Alternatively the equilibriated species are (i) dienolimine and enolimine-enaminone ((6Z)-3-hydroxy-6-(pyridin-2(1H)-ylidene)-4-(pyridine-2-yl)cyclohex-3-enone) or (ii) dienolimine, enolimine-enaminone and dienaminone ((4Z,6Z)-4,6-di(pyridin-2(1H)-ylidene)cyclohexane-1,3-dione). Benzoannulation of the pyridine ring at position 5,6 was found to increase the contribution of the tautomers which contain the enaminone moiety. Energies of the transition states between the stable tautomers were also calculated in order to estimate activation energy of the proton transfer. Values of the geometry based harmonic oscillator model of aromaticity (HOMA) index and Laplacian of the electron density in the hydrogen bond critical point (based on quantum theory of atom in molecules) shows that the enaminone moiety in the tautomers studied are stabilized by stronger intramolecular hydrogen bond than this present in the enolimine moiety.
密度泛函理论（DFT）计算在 B3LYP/6-311+G(d,p)水平表明 4,6-二（吡啶-2-基）环己烷-1,3-二酮是一种不稳定的化合物。另一方面，它的烯醇亚胺互变异构体（4,6-二（吡啶-2-基）环己烷-1,3-二烯-1,3-二醇）似乎足够稳定，可以在真空中存在。或者平衡的物种是（i）烯醇亚胺和烯醇亚胺-亚氨基酮（（6Z）-3-羟基-6-（吡啶-2（1H）-亚基）-4-（吡啶-2-基）环己-3-烯酮）或（ii）烯醇亚胺，烯醇亚胺-亚氨基酮和烯亚胺酮（（4Z,6Z）-4,6-二（吡啶-2（1H）-亚基）环己烷-1,3-二酮）。在位置 5,6 上的苯并环化发现增加了含有亚氨基酮部分的互变异构体的贡献。还计算了稳定互变异构体之间的过渡态的能量，以估计质子转移的活化能。基于几何的芳香性的谐振子模型（HOMA）指数和氢键临界点的电子密度拉普拉斯（基于分子中的原子量子理论）的值表明，在研究的互变异构体中的亚氨基酮部分通过更强的分子内氢键稳定，而不是在烯醇亚胺部分中存在的氢键。
