Time-Resolved Resonance Raman and Computational Investigation of the Influence of 4-Acetamido and 4-N-Methylacetamido Substituents on the Chemistry of Phenylnitrene

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• 作者：Jiadan Xue ; Shubham Vyas ; Yong Du ; Hoi Ling Luk ; Yung Ping Chuang ; Tracy Yuen Sze But ; Patrick H. Toy ; Jin Wang ; Arthur H. Winter ; David Lee Phillips ; Christopher M. Hadad ; Matthew S. Platz
• 刊名：Journal of Physical Chemistry A
• 出版年：2011
• 出版时间：July 7, 2011
• 年：2011
• 卷：115
• 期：26
• 页码：7521-7530
• 全文大小：1111K
• 年卷期：v.115,no.26(July 7, 2011)
• ISSN：1520-5215

文摘

A time-resolved resonance Raman (TR³) and computational investigation of the photochemistry of 4-acetamidophenyl azide and 4-N-methylacetamidophenyl azide in acetonitrile is presented. Photolysis of 4-acetamidophenyl azide appears to initially produce singlet 4-acetamidophenylnitrene which undergoes fast intersystem crossing (ISC) to form triplet 4-acetamidophenylnitrene. The latter species formally produces 4,4鈥?bisacetamidoazobenzene. RI-CC2/TZVP and TD-B3LYP/TZVP calculations predict the formation of the singlet nitrene from the photogenerated S₁ surface of the azide excited state. The triplet 4-acetamidophenylnitrene and 4,4鈥?bisacetamidoazobenzene species are both clearly observed on the nanosecond to microsecond time-scale in TR³ experiments. In contrast, only one species can be observed in analogous TR³ experiments after photolysis of 4-N-methylacetamidophenyl azide in acetonitrile, and this species is tentatively assigned to the compound resulting from dimerization of a 1,2-didehydroazepine. The different photochemical reaction outcomes for the photolysis of 4-acetamidophenyl azide and 4-N-methylacetamidophenyl azide molecules indicate that the 4-acetamido group has a substantial influence on the ISC rate of the corresponding substituted singlet phenylnitrene, but the 4-N-methylacetamido group does not. CASSCF analyses predict that both singlet nitrenes have open-shell electronic configurations and concluded that the dissimilarity in the photochemistry is probably due to differential geometrical distortions between the states. We briefly discuss the probable implications of this intriguing substitution effect on the photochemistry of phenyl azides and the chemistry of the related nitrenes.