Thermochemistry of the benzyl and allyl radicals and ions
Thermochemistry of the benzyl and allyl radicals and ions
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DOI：
10.1016/s0168-1176(96)04383-2
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发表时间：
1996-11-22
期刊：
影响因子：
--
通讯作者：
DePuy, CH
中科院分区：
文献类型：
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作者：
Ellison, GB;Davico, GE;DePuy, CH
我们研究了共振稳定自由基C6H5CH2和CH2CHCH2及其相应的阳离子和阴离子的热化学性质。流动余辉/选择离子流管仪器已被用来测量反应速率：可逆箭头可逆箭头速率常数的比值给出了每个反应的自由能变化，利用确定的CH3OH或H2O的气相酸度提供了酸度的值。我们计算熵变Delta（酸）S(300)（C6H5CH3）和Delta（酸）S(300)(CH2CHCH3)，提取Delta（酸）H(300)（C6H5CH3）和Delta（酸）H(300)（CH2CHCH3）的值。早期的光电子实验提供了苯基和烯丙基自由基的电离势和电子亲和力。利用ip和ea，再加上去质子化焓，可以得到300 K时的碳氢键焓和0 K时的碳氢键能。这些键能被用来计算自由基和离子的生成热以及阳离子氢化物的亲和，HA（所有值都以kcal mol（-1）为单位）：[图形]此外，我们发现δ（酸）G(300)(C6D5CD3) = 377.0 +/- 0.3 kcal mol（-1）。
We have studied the thermochemistry of the resonantly stabilized radicals, C6H5CH2 and CH2CHCH2 and their corresponding cations and anions. A flowing afterglow/selected ion flow tube instrument has been used to measure the rates of reaction: C6H5CH3 + CH3O- reversible arrow C6H5CH2- + CH3OHC6H5CH3 + CD3O- reversible arrow C6H5CH2- + CD3OHC6D5CD3 + CH3O- reversible arrow C6D5CD2- + CH3ODC6D5CD3 + CD3O- reversible arrow C6D5CD2- + CD3ODCH2CHCH3 + HO- reversible arrow CH2CHCH2- +H2OThe ratio of the rate constants gives a free energy change for each reaction and use of the established gas phase acidity of CH3OH or H2O provides values for the acidities. We calculate the entropy changes, Delta(acid)S(300)(C6H5CH3) and Delta(acid)S(300)(CH2CHCH3), to extract values for Delta(acid)H(300)(C6H5CH3) and Delta(acid)H(300)(CH2CHCH3). Earlier photoelectron experiments have provided ionization potentials and electron affinities for the benzyl and allyl radicals. Use of the IPs and EAs, together with the enthalpies of deprotonation, provides values for the C-H bond enthalpies at 300 K and the C-H bond energies at 0 K. These bond energies are used to compute the heats of formation of the radicals and ions as well as the cation hydride affinities, HA (all values in kcal mol(-1)):[GRAPHICS]In addition, we find Delta(acid)G(300)(C6D5CD3) = 377.0 +/- 0.3 kcal mol(-1).