理論研究β-thioxoketone相關分子的enol-enethiol互變異構作用及旋轉異構作用

Enol-Enethiol Tautomerism and Rotamerization of Related β-thioxoketones: A Theoretical Study

10.6202/THJ-2013-09-07

蔡明松(Ming-Sung Tsai)

enol-enethiol互變異構作用 ； 分子內氫鍵 ； 共振增強效應的氫鍵 ； enol-enethiol tautomerism ； β-thioxoketone ； rotamerism ； molecular hydrogen-bond ； resonance-assisted H-bond

慈惠學報

9期（2013 / 12 / 01）

82 - 97

繁體中文

本研究運用DFT（Density functional theory）方法探討β-thioxoketone 相關分子對enol-enethiol互變異構作用及旋轉異構作用的影響因素。在RB3LYP/6-31G**層次計算顯示在β-thioxoketone 分子的(Z)-enol的分子內氫鍵OH...S及enethiol的分子內氫鍵S-H...O比一般同類型的氫鍵強，且有低的能量障壁的質子轉移導致β-thioxoketone相關分子容易enol-enethiol互變異構作用，所以β-thioxoketone相關分子都是enol結構和enethiol結構的互變異構混合體。由於分子內氫鍵OH...S比SH...O強，因此(Z)-enol異構物比(Z)-enethiol異構物穩定，且是β-thioxoketone所有異構物中最穩定的。另外對β-thioxoketone相關分子而言，(Z)-enethiol異構物的SH...O氫鍵較弱（低於3.5 Kcal/mol），所以會形成沒有分子內氫鍵的開環結構及藉C-C單鍵旋轉產生(E)-enethiol異構物。研究也顯示enethiol異構物比enol異構物容易進行形成反式異構物。

The enol-enethiol tautomerism and (Z) form-(E) form rotamerism of β-thioxoketones, are discussed on the basis of B3LYP/6-31G** calculations. It is shown that the enol and enethiol tautomers of the β-thioxoketones be coexist. For (Z)-enol form, the more stable tautomer among the possible isomer of β-thioxoketones. The enol and the enethiol are interconverting rapidly due to the low energy barriers within the H-bonding framework of β-thioxoketones. Computations show that the low energy barriers of proton transfer for OH...S and SH...O intrmolecularly hydrogen-bonded in β-thioxoketones, because of because of because of because of because of the more delocalized charge distribution. The analysis of results lead to that only (Z)-enethiol can by rotamerism form non-proton chelated (Z)-enethiol and (E)-enethiol.

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