簡單烯醛類之光化學反應研究：產生乙醛基及異構化途徑

Photochemical Reactions of Simple Enones: Formation of Product Formyl Radical and Isomerization

李昇叡(Sheng Jui Lee) ； 何美霖(Mei-Lin Ho) ； 陳益佳(I-Chia Chen)

《化學》 62卷3期 (2004/09) Pp. 327-337

https://doi.org/10.6623/chem.2004025

摘要

簡單烯醛類如丙烯醛及巴豆醛，吾人利用雷射誘發螢光法測產物甲醛基，發現在波長193 nm激發下，丙烯醛可生成大量之電子基態甲醛基，但是巴豆醛卻無此自由基分解途徑，因此其反應生成甲醛基產物之途徑並不相同。吾人使用密度泛函理論，估算巴豆醛生成異構物及不同分解產物之途徑及能量，發現在單重態位能面之反應途徑主要有三種：(1)解離為丙烯及一氧化碳途徑、(2)經由氫原子轉移而產生巴豆醛之同分異構物、及(3)在氫原子轉移的同時，伴隨著解離產生甲醛分子的途徑。三重態(nπ^*)位能面下，具有更多之解離以及異構化途徑，可形成中間物 CH_3CHCH_2CO，再進行異構化成乙烯丙烯酮，亦可解離成propene + CO，所產生的丙烯為三重態而非單重態；或經由一能障斷鍵產生丙烯基及甲醛基，可異構化形成三重態之1,3-丁二烯醇，之後再進行反應形成三重態之3-丁烯醛(3-butenal)。於三重態(ππ^*)位能面下可越過一能障解離出甲基，或經由異構化途徑產生三重態之乙基乙烯酮，無論在單重或三重態位能面其異構化途徑均具有較低之能障，因此異構化對巴豆醛應是比分解更重要之反應途徑。

關鍵字

巴豆醛 ； 丙烯醛 ； 異構化

並列摘要

We employ laser-induced fluorescence to detect possible product HCO dissociated from simple enones. At 193-nm photolysis we detect significant amount of HCO from acrolein but less than 0.3% from crotonaldehyde (CH_3)HC=CH-COH). Because both acrolein and crotonaldehyde are simple enones but the dissociation channels are distinct, both dissociation and isomerization channels on the ground and the two lowest triplet surfaces of crotonaldehyde are studied using density functional theory (B3LYP/6-311++G(d,p)) as well as CCSD(T)/6-311G(d,p). On the singlet ground surface, dissociation channel: propene + CO and to fragment formaldehyde and isomerization channels to 1,3-butadienol and 3-butenal are found. On the triplet surface, isomerization processes to CH_3CHCH_2CHO and to ethyllketene are found. Several dissociation channels are calculated but with higher energy threshold than those for isomerization processes. The results of calculations imply that isomerization process should occur instead of direct dissociation on both singlet and triplet surfaces.

並列關鍵字

crotonaldehyde ； acrolein ； isomerization