Zhang Dan, Zhang Renyi
Department of Atmospheric Sciences, Texas A&M University, College Station, TX 77843, USA.
J Am Chem Soc. 2002 Mar 20;124(11):2692-703. doi: 10.1021/ja011518l.
The formation and unimolecular reactions of primary ozonides and carbonyl oxides arising from the O(3)-initiated reactions of isoprene have been investigated using density functional theory and ab initio molecular orbital calculations. The activation energies of O(3) cycloaddition to the two double bonds of isoprene are found to be comparable (3.3-3.4 kcal mol(-1)), implying that the initial two O(3) addition pathways are nearly equally accessible. The reaction energies of O(3) addition to isoprene are between -47 and -48 kcal mol(-1). Cleavage of primary ozonides to form carbonyl oxides occurs with a barrier of 11-16 kcal mol(-1) above the ground state of the primary ozonide, and the decomposition energies range from -5 to -13 kcal mol(-1). OH formation is shown to occur primarily via decomposition of the carbonyl oxides with the syn-positioned methyl (alkyl) group, which is more favorable than isomerization to form dioxirane (by 1.1-3.3 kcal mol(-1)). Using the transition-state theory and master equation formalism, we determine an OH yield of 0.25 from prompt and thermal decomposition of the carbonyl oxides.
利用密度泛函理论和从头算分子轨道计算方法，研究了异戊二烯与O(3)引发反应生成的初级臭氧化物和羰基氧化物的形成及单分子反应。发现O(3)与异戊二烯的两个双键进行环加成反应的活化能相当（3.3 - 3.4 kcal mol(-1)），这意味着最初的两条O(3)加成途径几乎具有相同的可及性。O(3)与异戊二烯加成反应的反应能在-47至-48 kcal mol(-1)之间。初级臭氧化物裂解形成羰基氧化物的过程中，能垒比初级臭氧化物基态高出11 - 16 kcal mol(-1)，分解能在-5至-13 kcal mol(-1)范围内。研究表明，OH的形成主要通过羰基氧化物与处于顺位的甲基（烷基）发生分解反应，这比异构化形成二氧杂环丙烷更有利（相差1.1 - 3.3 kcal mol(-1)）。利用过渡态理论和主方程形式，我们确定由羰基氧化物的快速和热分解产生的OH产率为0.25。
