The γ-radiolysis of 1-arylcyclopentenes [Ar = Ph (1a); 4-ClC6H4 (1b); 4-MeC6H4 (1c); 4-MeOC6H4 (1d)] at 77 K initially gave transient absorption bands attributable to their monomer cation radicals (1a·+—1d·+), with λmax around 400 and 650—730 nm. In the case of 1a, 1b, and 1c, simultaneous formation of new absorption bands with λmax around 480—500 nm, attributable to the dimer cation radicals, was clearly observed upon warming along with a decrease in the monomer cation radical absorption bands. Using 355-nm laser photolysis at room temperature and an N-methylquinolinium salt as an electron acceptor, the rate constants for the formation of the dimer cation radicals (kdimer) and the reaction-rate constants for 1·+ with methanol (kMeOH) were determined. The reactivities of 1·+ with 1 and with methanol are discussed on the basis of the results obtained by a semiempirical molecular orbital calculation using the PM3 method. The results indicate that the reactivities of 1·+ depend not on its structure but on the charge density of the ethylene bond. In addition, dimerization of the cycloalkene cation radicals with larger ring size than 1, such as 1-phenylcyclohexene, 1-phenylcycloheptene, and 1-phenylcyclooctene cation radicals, was found to be remarkably dependent on the ring size.
1- 芳基
环戊烯 [Ar = Ph (1a);4-ClC6H4 (1b);4-MeC6H4 (1c);4-MeOC6H4 (1d)]在 77 K 下的γ-射线分解最初产生了可归因于其单体阳离子自由基(1a-+-1d-+)的瞬时吸收带,λmax 分别为 400 纳米和 650-730 纳米。在 1a、1b 和 1c 的情况中,升温后明显观察到同时形成了新的吸收带,λmax 约为 480-500 纳米,归因于二聚阳离子自由基,同时单体阳离子自由基的吸收带有所减少。在室温下使用 355-nm 激光光解和 N-甲基
喹啉盐作为电子受体,测定了二聚阳离子自由基的形成速率常数(kdimer)和 1-+ 与
甲醇的反应速率常数(kMeOH)。根据使用 PM3 方法进行半经验分子轨道计算得出的结果,讨论了 1-+ 与 1 和
甲醇的反应活性。结果表明,1-+ 的反应活性并不取决于其结构,而是取决于
乙烯键的电荷密度。此外,研究还发现环径大于 1 的环烯阳离子自由基(如 1-苯基
环己烯、1-苯基
环庚烯和 1-苯基环
辛烯阳离子自由基)的二聚化明显取决于环径。