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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Unusual photochemical C-N bond cleavage in the novel methyl 2-Chloro-3-methyl-2H-azirine-2-carboxylate
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Unusual photochemical C-N bond cleavage in the novel methyl 2-Chloro-3-methyl-2H-azirine-2-carboxylate

机译：新型2-氯-3-甲基-2H-叠氮基-2-羧酸甲酯中异常的光化学C-N键裂解

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摘要

The structure, preferred conformers, vibrational spectrum, and photochemical behavior of the novel azirine, methyl 2-chloro-3-methyl-2H-azirine-2-carboxylate (MCMAC) were investigated in low-temperature matrixes and in the neat solid amorphous state by infrared spectroscopy and quantum-chemical calculations. Two conformers of the compound were observed in argon, krypton, and xenon matrixes, in agreement with the DFT(B3LYP)/6-311++G(d,p) and MP2/6-311++G(d,p) theoretical calculations. Both conformers were found to exhibit the carboxylic ester group in the cis conformation, differing in the arrangement defined by the O=C-C-Cl dihedral angle (cis and trans, for Ct and Cc forms, respectively). The Ct conformer was found to be the most stable conformer in the gaseous phase as well as in both argon and krypton matrixes, whereas the more polar Cc conformer became the most stable form in the xenon matrix and in the neat solid amorphous phase. In situ broadband UV (lambda > 235 nm) excitation of matrix-isolated MCMAC led to azirine ring C-C and C-N bond cleavages, the latter process corresponding to the most efficient reaction channel. The photochemical cleavage of the C-N bond had never been previously observed in the case of aliphatic 2H-azirines. Two electron withdrawing substituents (methoxycarbonyl group and chlorine atom) are connected to the azirine ring in the novel MCMAC azirine. The simultaneous presence of these two groups accelerates intersystem crossing toward the triplet state where cleavage of the C-N bond takes place. The primary photoproducts resulting from the C-N and C-C ring-opening reactions were also found to undergo further photochemical decarbonylation or decarboxylation reactions.
机译：在低温基质和纯固体无定形状态下研究了新型叠氮基2-氯-3-甲基-2H-叠氮基-2-羧酸甲酯（MCMAC）的结构，优选构象，振动光谱和光化学行为通过红外光谱和量子化学计算。与DFT（B3LYP）/ 6-311 ++ G（d，p）和MP2 / 6-311 ++ G（d，p）一致，在氩气，k气和氙气基质中观察到该化合物的两个构象异构体理论计算。发现两个构象异构体均显示出顺式构象的羧酸酯基，其区别在于由O ＝ C-C-Cl二面角定义的排列（对于Ct和Cc形式分别为顺式和反式）。发现Ct构象异构体在气相中以及在氩气和k基体中都是最稳定的构象异构体，而极性更强的Cc构象异构体在氙气基质和纯净的固态无定形相中成为最稳定的形式。基质分离的MCMAC的原位宽带UV（λ> 235 nm）激发导致叠氮环C-C和C-N键断裂，后者对应于最有效的反应通道。以前从未在脂肪族2H-叠氮基的情况下观察到C-N键的光化学裂解。在新型的MCMAC叠氮基中，两个吸电子取代基（甲氧羰基和氯原子）与叠氮基环相连。这两个基团的同时存在加速了系统间向三重态的交叉，在三重态中发生了C-N键的裂解。还发现了由C-N和C-C开环反应产生的初级光产物进一步进行光化学脱羰或脱羧反应。

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