Photolysis of (3-Methyl-2H-azirin-2-yl)-phenylmethanone: Direct Detection of a Triplet Vinylnitrene Intermediate

被引:29
|
作者
Rajam, Sridhar [1 ]
Murthy, Rajesh S. [1 ]
Jadhav, Abhijit V. [1 ]
Li, Qian [1 ]
Keller, Christopher [1 ]
Carra, Claudio [3 ]
Pace, Tamara C. S. [2 ]
Bohne, Cornelia [2 ]
Ault, Bruce S. [1 ]
Gudmundsdottir, Anna D. [1 ]
机构
[1] Univ Cincinnati, Dept Chem, Cincinnati, OH 45221 USA
[2] Univ Victoria, Dept Chem, Victoria, BC, Canada
[3] Univ Space Res Assoc, Div Space Life Sci, Houston, TX 77058 USA
来源
JOURNAL OF ORGANIC CHEMISTRY | 2011年 / 76卷 / 24期
基金
美国国家科学基金会; 加拿大自然科学与工程研究理事会;
关键词
LASER FLASH-PHOTOLYSIS; N BOND-CLEAVAGE; 2ND-ORDER PERTURBATION-THEORY; DENSITY-FUNCTIONAL THEORY; PHOTOELECTRON-SPECTROSCOPY; SELECTIVE FORMATION; MOLECULAR-OXYGEN; ALKYL NITRENES; C-C; PHOTOCHEMISTRY;
D O I
10.1021/jo200877k
中图分类号
O62 [有机化学];
学科分类号
070303 ; 081704 ;
摘要
The photoreactivity of (3-methyl-2H-azirin-2-yl)-phenylmethanone, 1, is wavelength-dependent (Singh et al. J. Am. Chem. Soc. 1972, 94, 1199-1206). Irradiation at short wavelengths yields 2P, whereas longer wavelengths produce 3P. Laser flash photolysis of 1 in acetonitrile using a 355 nm laser forms its triplet ketone (T-1K, broad absorption with lambda(max) similar to 390-410 nm, tau similar to 90 ns), which cleaves and yields triplet vinylnitrene 3 (broad absorption with lambda(max) similar to 380-400 nm, tau = 2 mu s). Calculations (B3LYP/6-31+G(d)) reveal that T-1K of 1 is located 67 kcal/mol above its ground state (S-0) and has a long C-N bond (1.58 angstrom), and the calculated transition state to form 3 is only 1 kcal/mol higher in energy than T-1K of 1. The calculations show that 3 has significant 1,3-carbon iminyl biradical character, which explains why 3 reacts efficiently with oxygen and decays by intersystem crossing to the singlet surface. Photolysis of 1 in argon matrixes at 14 K produced ketene imine 7, which presumably is formed from 3 intersystem crossing to 7. In comparison, photolysis of 1 in methanol with a 266 nm laser produces mainly ylide 2 (lambda(max) similar to 380 nm, tau similar to 6 mu s, acetonitrile), which decays to form 2P. Ylide 2 is formed via singlet reactivity of 1, and calculations show that the first singlet excited state of the azirine chromophore (S-1A) is located 113 kcal/mol above its So and that the singlet excited state of the ketone (S-1K) is 85 kcal/mol. Furthermore, the transition state for cleaving the C-C bond in 1 to form 2 is located 49 kcal/mol above the So of 1. Thus, we theorize that internal conversion of S-1A to a vibrationally hot S-0 of 1 forms 2, whereas intersystem crossing from S-1K to T-1K results in 3.
引用
收藏
页码:9934 / 9945
页数:12
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