利用間質隔離法研究isobutene + Cl在p-H2間質中之反應

Abstract

此研究利用低溫間質隔離技術搭配霍氏轉換紅外光譜儀(FTIR)研究異丁烯與Cl在para-H2 (p-H2)間質中進行加成反應所產生之中間體。i-C4H8/Cl2/p-H2間質經365 nm光照射後產生新的譜線，在二次光解後可依不同光解波長下之消失比例，將譜線分為A、B兩群組，分別指派為Cl反應至末端及中間碳上之自由基產物(˙C(CH3)2CH2Cl及˙CH2CCl(CH3)2)。其中可觀察到˙C(CH3)2CH2Cl較強之譜線位於534.5/532.1、1001.0、1212.9/1210.8及1366.0 cm1，對應理論計算之簡諧振動波數依序為：14 (C(1)-Cl伸張)、12 (C(3)H3(C(4)H3)同相形變)、10 (C(1)H2搖擺)及25 (C(3)H3(C(4)H3)異相傘狀振動)。而˙CH2CCl(CH3)2較強之譜線位於642.7、1371.8及1098.2 cm-1，而其對應之理論計算簡諧振動波數依序為：13 (662 cm-1，C(1)H2搖擺)、25 (1394 cm-1，C(3)H3(C(4)H3)異相傘狀振動)及10 (1107 cm-1，C(3)H2(C(4)H2)同相形變)。除此之外，亦以37Cl及13C同位素位移來進一步確認譜線之指派，反應在中間/末端碳上之分歧比例約為3±1。 實驗中觀測到Cl原子加成到C=C鍵之兩端，和本實驗室以前觀測到Cl原子只加成到丙烯的中間碳及只加成到1,3-丁二烯的末端碳都不相同，顯示晶格效應會影響反應之途徑。

The reactions of chlorine atom with isobutene in solid para-hydrogen (p- H2) were investigated with infrared (IR) absorption spectra. When a p-H2 matrix containing Cl2 and isobutene was irradiated with ultraviolet light at 365 nm, two groups of new line appeared; they diminished differently when secondary photolysis at varied wavelength was performed. Intense lines at 534.5/532.1、1001.0、1212.9/1210.8 and 1366.0 cm1, and several weaker ones are assigned to the 1-chloro-2-methyl-2-propyl radical (˙C(CH3)2CH2Cl), whereas those with intense ones at 642.7、1371.8 and 1098.2 cm-1, and several weaker ones are assigned to the 2-chloro-2-methylpropyl (˙CH2CCl(CH3)2). Observed wavenumbers and relative intensities agree with the scaled harmonic vibrational wavenumbers and IR intensities predicted with the B3PW91/aug-cc-pVTZ method.The branching ratio for formation of ˙C(CH3)2CH2Cl to˙CH2CCl(CH3)2 are 3±1. In this experiment, the Cl atom adds not only to the terminal but also center carbon atom of isobutene, which is different from our previous observation of Cl adding to the central carbon of propene and Cl adding to the terminal carbon of 1,3-butadiene. The matrix cage effect plays a critical role in affection the reaction paths in solid p-H2.