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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Direct Gas-Phase Kinetic Studies of Silylene Addition Reactions: SiH_2 + C_3H_6, SiH_2 + i-C_4H_8, and SiMe_2 + C_2H_4. The Effects of Methyl Substitution on Strain Energies in Siliranes
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Direct Gas-Phase Kinetic Studies of Silylene Addition Reactions: SiH_2 + C_3H_6, SiH_2 + i-C_4H_8, and SiMe_2 + C_2H_4. The Effects of Methyl Substitution on Strain Energies in Siliranes

机译：甲硅烷基加成反应的直接气相动力学研究：SiH_2 + C_3H_6，SiH_2 + i-C_4H_8和SiMe_2 + C_2H_4。甲基取代对Siliranes菌株能量的影响

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Time-resolved studies of the title reactions have been carried out over the pressure range 1-100 Torr (in SF_6 bath gas) and at temperatures in the range 293-600 K, using laser flash photolysis techniques to generate and monitor the silylenes, SiH_2 and SiMe_2. All three reactions showed evidence of pressure dependence, consistent with third-body assisted association reactions to form silirane products. Extrapolation of the pressure-dependent rate constants gave the following Arrhenius parameters: SiH_2 + C_3H_6, log(A/cm~3 molecule~(-1) s~(-1)) = -9.79 ± 0.03, E_a (kJ mol~(-1)) = -1.9 ± 0.3; SiH_2 + C_4H_8, log(A/cm~3 molecule~(-1) s~(-1) = -9.91 ± 0.04, E_a (kJ mol~(-1)) = -2.5 ± 0.3; SiMe_2 + C_4H_8, long(A/cm~3 molecule~(-1) s~(-1)) = -12.12 ± 0.02, E_a (kJ mol~(-1)) = -8.5 ± 0.2. These parameters are consistent with fast, nearly collision-controlled processes for SiH_2 but a tighter transition state for SiMe_2. Rice, Ramsperger, Kassel, Marcus theory (RRKM) modeling, based on consistent transition states for silirane decomposition, and employing a weak collisional deactivation model, gave good fits to the pressure-dependent curves for each system, provided an appropriate value of E_o (fitting parameter) was used for each reaction. The kinetic results are consistent with an electrophilically led addition mechanism, although methyl substitution in the alkene hardly affects the rate constants. The RRKM-derived E_o values have been used to derive reaction enthalpies which are in reasonable agreement with values obtained by ab initio calculations at the G2 (MP2,SVP) level. The experimental ΔH°values yield strain energies of 190, 196, and 216 kJ mol~(-1) for 2-methyl-, 2,2-dimethyl-, and 1,1-dimethylsilirane, respectively. Compared to the strain enthalpy of 167 kJ mol~(-1) for silirane itself, this shows that methyl substituents in the silirane products substantially increase the strain energies. Theory supports this.
机译：使用激光闪光光解技术在1-100 Torr的压力范围（在SF_6浴气体中）和293-600 K的温度范围内，进行了标题反应的时间分辨研究，以生成和监控SiH_2和SiMe_2。所有这三个反应均显示出压力依赖性的证据，这与第三体辅助缔合反应形成硅丙烷产物相一致。压力依赖性速率常数的外推给出以下Arrhenius参数：SiH_2 + C_3H_6，log（A / cm〜3分子〜（-1）s〜（-1））= -9.79±0.03，E_a（kJ mol〜（ -1））= -1.9±0.3; SiH_2 + C_4H_8，log（A / cm〜3分子〜（-1）s〜（-1）= -9.91±0.04，E_a（kJ mol〜（-1））= -2.5±0.3; SiMe_2 + C_4H_8，长（A / cm〜3分子〜（-1）s〜（-1））= -12.12±0.02，E_a（kJ mol〜（-1））= -8.5±0.2。这些参数与快速，几乎碰撞SiH_2的过程受控，但SiMe_2的过渡态更严格。Rice，Ramsperger，Kassel，Marcus理论（RRKM）建模基于硅烷化分解的一致过渡态并采用弱碰撞失活模型，非常适合压力-依赖于每个系统的曲线，只要为每个反应使用合适的E_o（拟合参数）值，尽管烯烃中的甲基取代几乎不会影响速率常数，动力学结果与亲电引发的加成机理是一致的。 E_o值已被用于导出反应焓，该焓与在G2（MP2，SVP）级别从头算获得的值合理地吻合。实验的ΔH°值对2-甲基-，2,2-二甲基-和1,1-二甲基甲硅烷分别产生190、196和216kJ mol〜（-1）的应变能。与硅烷本身的167 kJ mol〜（-1）的应变焓相比，这表明硅烷硅烷产物中的甲基取代基大大增加了应变能。理论支持这一点。

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