What Definitively Controls the Photochemical Activity of Methylbenzonitriles and Methylanisoles? Insights from Theory
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- 作者：Xuefei Xu ; Zexing Cao ; Qianer Zhang
- 刊名：Journal of Physical Chemistry A
- 出版年：2007
- 出版时间：July 5, 2007
- 年：2007
- 卷：111
- 期：26
- 页码：5775 - 5783
- 全文大小：612K
- 年卷期：v.111,no.26(July 5, 2007)
- ISSN：1520-5215
文摘
CASPT2//CASSCF and B3LYP methodologies have been used to study the excited-state properties andphotochemical isomerizations of p-, m-, and o-methylbenzonitriles and methylanisoles. Calculations showthat the biradical mechanism is the most favored channel for the photoinduced interconversion of p-, m- ando-methylbenzonitriles, both dynamically and thermodynamically. The formation of biradical as a keyintermediate is highly selective, and only the biradicals with a turned-up cyano-substituted carbon are involvedin photoisomerization. Methylanisole isomers are inactive relative to methylbenzonitriles at 254 nm. Suchremarkable activity difference between methylbenzonitrile and methylanisole in photochemistry arises fromthe accessibility of the S1/S0 conical intersection as well as the stability of prefulvene biradicals. Formethylanisoles, the S1/S0 precursor and the reactive biradicals are inaccessible at 254 nm, which should bethe origin of inactivity. The results suggest that the conical intersection accessibility plays a crucial role inthe photochemistry of substituted benzenes at 254 nm.