7种常用加香物质的酮式-烯醇式互变异构计算

A computation of keto-enol tautomerism for senven frequently used flavors

为了解7种可能发生酮式-烯醇式互变异构的常用加香物质存在形式,在气相和水相B3LYP/6-311++G(2d,2p)水平进行了结构优化和过渡态计算,并在MP2/6-311++G(2d,2p)∥B3LYP/6-311++G(2d,2p)水平计算了单点能.结果显示:(1)甲基环戊烯醇酮、3,4-二甲基-1,2-环戊二酮、1-甲基-2,3-环己二酮、4-羟基-2,5-二甲基-3(2H)-呋喃酮、麦芽酚的过渡态活化能较高,在室温甚至水催化条件下都不能发生酮式-烯醇式互变异构,这5种物质烯醇式能量低于酮式;(2)在室温水催化条件下2,3-丁二酮和α-当归内酯可以发生酮式-烯醇式互变异构,这2种物质酮式能量低于烯醇式;(3)这7种物质酮式-烯醇式互变异构时,2分子水催化的八元环过渡态活化能都显著低于无水催化的四元环过渡态和1分子水催化的六元环过渡态.

In order to investigate the existence form for seven frequently used flavors which may make ketoenol tautomerism,their structures and transition states are calculated at B3LYP/6-311 ＋＋G （2d, 2p） level in both gas and water phase respectively. Meanwhile, the single point energies are calculated at MP2/6-311 ＋ ＋G （ 2d, 2p）//B3LYP/6-311 ＋＋G （ 2d, 2p） level.The calculation results show that the activation energies for transition state of methylcyclopentenolone, 3,4-dimethyl- 1,2-cyclopentadione, 1 -methyl-2,3-cyclohexadione, 4-hy- droxy-2,5-dimethyl-3（2H）-furanone and maltol are too high to proceed keto-enol tautomerizm at room tem- perature even when catalyzed by water.The relative energies of the enol forms for the five substances are lower than their keto forms. As for 2,3-diketobutane and α- angelicalactone, they can make keto-enol tautomerizm when catalyzed by water at room temperature. And the relative energies of the keto forms for the two flavors are lower than their enol forms. The activation energy of the eight-membered ring transition state for seven compounds,which involving two water molecules for keto-enol tautomerism, are all significantly lower than those of no water catalyzed four-membered ring and those of one water molecule catalyzed six-membered ring transition state.