Amicangelo Jay C, Lee Yuan-Pern
School of Science, Penn State Erie, The Behrend College , 4205 College Drive, Erie, Pennsylvania 16563, United States.
Department of Applied Chemistry and Institute of Molecular Science, National Chiao Tung University , Hsinchu 30010, Taiwan.
J Phys Chem A. 2017 Nov 22;121(46):8771-8784. doi: 10.1021/acs.jpca.7b07922. Epub 2017 Nov 8.
The reaction of chlorine atoms (Cl) with isoprene (2-methyl-1,3-butadiene, CH) in solid para-hydrogen (p-H) matrices at 3.2 K was studied using infrared (IR) spectroscopy. Mixtures of CH and Cl were codeposited in p-H at 3.2 K, followed by irradiation with ultraviolet light at 365 nm to induce the photodissociation of Cl and the subsequent reaction of the Cl atoms with CH. Upon 365 nm photolysis, a multitude of new lines appeared in the IR spectrum, and, based on the secondary photolysis behavior, it was determined that the majority of the new lines belong to two distinct chemical species, designated as set A (intense lines at 1237.9, 807.8, and 605.6/608.2 cm, and several other weaker lines) and set B (intense lines at 942.4, 1257.7, 796.7/798.5, 667.9, and 569.7 cm, and several other weaker lines). Quantum-chemical calculations were performed at the B3PW91/6-311++G(2d,2p) level for ·CH and the four possible isomers of the ·CHCl radicals, produced from the addition of the Cl atom to the four distinct sites of carbon atoms in CH, to determine the relative energetics and predict IR spectra for each radical. The newly observed lines of sets A and B are assigned to the 1-chloromethyl-2-methylallyl radical (addition to carbon 4) and the 1-chloromethyl-1-methylallyl radical (addition to carbon 1) according to comparison with predicted IR spectra of possible products. The 1-chloromethyl-2-methylallyl radical and 1-chloromethyl-1-methylallyl radicals were predicted to be the most stable, with the latter ∼8 kJ mol lower in energy than the former. The ratio of the 1-chloromethyl-1-methylallyl to the 1-chloromethyl-2-methylallyl radicals is estimated to be (1.2 ± 0.5):1.0, indicating that the two radicals are produced in approximately equal amounts. The exclusive production of the radicals involving the addition of the Cl atom to the two terminal carbons of isoprene is analogous to what was previously observed for the reaction of Cl atoms with trans-1,3-butadiene in solid p-H.
利用红外光谱研究了氯原子（Cl）与异戊二烯（2-甲基-1,3-丁二烯，CH）在3.2 K的固态对氢（p-H）基质中的反应。将CH和Cl的混合物在3.2 K下共沉积于p-H中，然后用365 nm的紫外光照射，以诱导Cl的光解离以及随后Cl原子与CH的反应。在365 nm光解后，红外光谱中出现了大量新谱线，基于二次光解行为，确定大多数新谱线属于两种不同的化学物种，分别指定为A组（在1237.9、807.8和605.6/608.2 cm处有强谱线，以及其他几条较弱谱线）和B组（在942.4、1257.7、796.7/798.5、667.9和569.7 cm处有强谱线，以及其他几条较弱谱线）。在B3PW91/6-311++G(2d,2p)水平上对·CH以及·CHCl自由基的四种可能异构体进行了量子化学计算，这些异构体是由Cl原子加成到CH中四个不同碳原子位点上产生的，以确定相对能量并预测每个自由基的红外光谱。根据与可能产物预测红外光谱的比较，将新观察到的A组和B组谱线分别归属为1-氯甲基-2-甲基烯丙基自由基（加成到碳4上）和1-氯甲基-1-甲基烯丙基自由基（加成到碳1上）。预测1-氯甲基-2-甲基烯丙基自由基和1-氯甲基-1-甲基烯丙基自由基最稳定，后者的能量比前者低约8 kJ/mol。估计1-氯甲基-1-甲基烯丙基自由基与1-氯甲基-2-甲基烯丙基自由基的比例为(1.2±0.5):1.0，表明这两种自由基的生成量大致相等。涉及Cl原子加成到异戊二烯两个端基碳原子上的自由基的唯一生成情况与之前在固态p-H中观察到的Cl原子与反式-1,3-丁二烯反应的情况类似。
