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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >One- and two-photon-induced ring-cleavage reactions of strained benzocycloalkenes via hot molecules
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One- and two-photon-induced ring-cleavage reactions of strained benzocycloalkenes via hot molecules

机译：通过热分子对苯并环烯烃的单光子诱导和双光子诱导的环裂解反应

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The ring-cleavage reactions of a series of benzocycloalkenes were studied using an ArF excimer laser. Product formation was significantly suppressed in the presence of nitrogen; therefore, the presence of vibrationally excited states (hot molecules), as intermediates, was indicated. The product of highly strained benzocyclobutene was linearly proportional to the laser fluence, whereas those of benzocyclopentene and benzocyclohexene were proportional to the square of the laser fluence in the presence of nitrogen. These phenomena cannot be understood as photochemical bond cleavage in the electronic excited state, but instead appear to be the result of single- and two-photon reactions of hot molecules. The dissociation rate constants were evaluated by a statistical rate theory under the assumption that the reaction occurred from the hot molecule. The reaction rate of highly strained benzocyclobutene was predicted to be faster than the collisional rate with foreign gas, even if it had vibrational energy equivalent to one photon; however, the reaction rates of less strained benzocyclohexene were expected to compete with the collisional rate when the vibrational energy was equivalent to two photons. Benzocyclopentene was an intermediate case and showed both single- and two-photon reactions. The dissociation rate constant of 1.4 x 10(6) s(-1) was successfully obtained from benzocyclopentene under collision-free conditions. This value was in fair agreement with the calculated value. The different dissociation rate constants of the molecules were well-explained in terms of the strain energy. Although the strain energy varies in a wide range (10-130 kJ mol(-1)), the simple model of the calculations reproduced the observed values of the CH2-CH2 bond dissociation in strained benzocycloalkenes.
机译：使用ArF受激准分子激光器研究了一系列苯并环烯烃的开环反应。在氮存在下，产物的形成被显着抑制;因此，表明存在作为中间体的振动激发态（热分子）。在氮气存在下，高应变苯并环丁烯的乘积与激光通量成线性比例，而苯并环戊烯和苯并环己烯的乘积与激光通量的平方成比例。这些现象不能理解为在电子激发态下的光化学键断裂，而是看起来是热分子的单光子和双光子反应的结果。在反应发生于热分子的假设下，通过统计速率理论评估解离速率常数。预测高应变的苯并环丁烯的反应速率比与异物的碰撞速率快，即使它具有相当于一个光子的振动能量也是如此。然而，当振动能量等于两个光子时，应变较小的苯并环己烯的反应速率有望与碰撞速率竞争。苯并环戊烯是一种中间情况，显示出单光子反应和双光子反应。在无碰撞条件下，成功地从苯并环戊烯获得了1.4 x 10（6）s（-1）的解离速率常数。该值与计算值完全一致。分子的不同解离速率常数在应变能方面得到了很好的解释。尽管应变能在很宽的范围内变化（10-130 kJ mol（-1）），但简单的计算模型再现了在应变的苯并环烯烃中CH2-CH2键解离的观测值。

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