Department of Applied Chemistry and Institute of Molecular Science, National Chiao Tung University, Hsinchu 30010, Taiwan.
J Chem Phys. 2011 Nov 7;135(17):174302. doi: 10.1063/1.3653988.
We applied infrared matrix isolation spectroscopy to investigate the reactions between Cl atom and acetylene (C₂H₂) in a para-hydrogen (p-H₂) matrix at 3.2 K; Cl was produced via photodissociation at 365 nm of matrix-isolated Cl₂ in situ. The 1-chloroethyl radical (·CHClCH₃) and chloroethene (C₂H₃Cl) are identified as the main products of the reaction Cl + C₂H₂ in solid p-H₂. IR absorption lines at 738.2, 1027.6, 1283.4, 1377.1, 1426.6, 1442.6, and 2861.2 cm⁻¹ are assigned to the 1-chloroethyl radical. For the reaction of Cl + C₂D₂, lines due to the ·CDClCH₂D radical and trans-CHDCDCl are observed; the former likely has a syn-conformation. These assignments are based on comparison of observed vibrational wavenumbers and ¹³C- and D-isotopic shifts with those predicted with the B3LYP/aug-cc-pVDZ and MP2/aug-cc-pVDZ methods. Our observation indicates that the primary addition product of Cl + C₂H₂, 2-chlorovinyl (·CHCHCl) reacts readily with a neighboring p-H2 molecule to form ·CHClCH₃ and C₂H₃Cl. Observation of ·CDClCH₂D and trans-CHDCDCl from Cl + C₂D₂ further supports this conclusion. Although the reactivity of p-H₂ appears to be a disadvantage for making highly reactive free radicals in solid p-H₂, the formation of 1-chloroethyl radical indicates that this secondary reaction might be advantageous in producing radicals that are difficult to prepare from simple photolysis or bimolecular reactions in situ.
我们应用红外矩阵隔离光谱法研究了在 3.2 K 的 para 氢（p-H₂）基质中氯原子与乙炔（C₂H₂）之间的反应；Cl 通过 365nm 光解原位生成的矩阵隔离 Cl₂产生。在固态 p-H₂中，反应 Cl+C₂H₂的主要产物为 1-氯乙基自由基（·CHClCH₃）和氯乙烷（C₂H₃Cl）。IR 吸收线在 738.2、1027.6、1283.4、1377.1、1426.6、1442.6 和 2861.2cm⁻¹被分配给 1-氯乙基自由基。对于 Cl+C₂D₂的反应，观察到·CDClCH₂D 自由基和反式-CHDCDCl 的谱线；前者可能具有顺式构象。这些分配是基于与用 B3LYP/aug-cc-pVDZ 和 MP2/aug-cc-pVDZ 方法预测的观察到的振动波数和 ¹³C 和 D 同位素位移的比较。我们的观察表明，Cl+C₂H₂的主要加成产物 2-氯乙烯基（·CHCHCl）很容易与相邻的 p-H2 分子反应，形成·CHClCH₃和 C₂H₃Cl。Cl+C₂D₂中观察到的·CDClCH₂D 和反式-CHDCDCl 进一步支持了这一结论。尽管 p-H₂的反应性似乎不利于在固态 p-H₂中生成高反应性自由基，但 1-氯乙基自由基的形成表明，这种二次反应可能有利于生成难以通过简单光解或双分子反应原位制备的自由基。
