理論方法研究環烯醇類化合物自由基的酮-烯醇互變異構

Theoretical study of Radical Keto-Enol Tautomerism of Cyclic Enol Derivatives

陳威宏(Chen, Weihong)

指導教授 ： 李錫隆

國立中正大學/理學院/化學暨生物化學系/碩士(2012年)

摘要

在本研究中，我們利用不同的DFT及MP2方法搭配6-31+G**基組去探討酮-烯醇互變異構過程的烯醇式與酮式之間的相對穩定度以及反應的Energy Barrier，結構從最小的乙烯醇、3-methylbut-1-en-1-ol、3-methylcyclohex-1-enol到最大的4-(3-hydroxycyclohex-2-enyl) butanal，包括中性(Neutral)、自由基陽離子(Radical Cation)、自由基陰離子(Radical Anion)以及中性的自由基(Neutral Radical)系統，研究結果顯示對於β位置有一Radical且維持電中性的系統，其酮-烯醇互變異構過程中的烯醇式較為穩定，此外MP2方法在計算此系統中存在著極大的誤差，而M06-2X相對而言則是較適合的計算方法。取代基會影響酮-烯醇互變異構過程中碳-碳間及碳-氧間的鍵長變化，這些鍵長的變化會使得自由基delocalized的效果改變，烯醇式的穩定性也會改變，進一步影響Keto-Enol Tautomerism Energy及Energy barrier。極性溶劑的確可以幫助酮-烯醇互變異構中質子轉移的過程，大大地降低Energy Barrier。

關鍵字

酮-烯醇互變異構

並列摘要

In this study, different DFT methods and MP2 with 6-31+G** basis set were used to investigate Keto-Enol tautomerism. For comparison, many different structures were chosen, including neutral, radical cation and radical anion of vinyl alcohol system, neutral and neutral radical of 3-methylbut-1-en-1-ol, 3-methylcyclohex-1-enol and 4-(3-hydroxycyclohex-2-enyl) butanal system.It is found that for most cases, Keto form is more stable than enolic structure.Only in β-position neutral radical system, the enolic structure is more stable.It is interesting to find that MP2 gives different result in contrast to M06-2X and B3LYP calculation method. The bond length change between C6 and O7 would be affected by the delocalized electron between C6 and O7, then the stability of Enol form would be changed. Polar solvents such as H2O and CH3OH are found to reduce greatly the energy barrier of the Keto-Enol Tautomerism.

並列關鍵字

Keto-Enol Tautomerism

參考文獻

5. Hsu, D.-S.; Hsu, C.-W. Tetrahedron Lett. 2012, 53, 2185-2188.

9. Saunders, W. H. J. Am. Chem. Soc. 1994,116, 5400-5404.

14. Bertrand, W.; Bouchoux, G. Rapid Commun. Mass Spectrom. 1998, 12, 1697-1700.

17. Holmesla, J. L.; Lossing, F. P. J. Am. Chem. Soc. 1980, 102,1591-1595.

26. Fu, A.; Li, H.; Du, D. J. Mol. Stuuct-Theochem. 2006, 767, 51-60.