Competitive threshold collision-induced dissociation: Gas-phase acidities and bond dissociation energies for a series of alcohols
Competitive threshold collision-induced dissociation: Gas-phase acidities and bond dissociation energies for a series of alcohols
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DOI：
10.1021/jp991459m
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发表时间：
1999-09-02
影响因子：
2.9
通讯作者：
Ervin, KM
中科院分区：
文献类型：
--
作者：
DeTuri, VF;Ervin, KM
本文采用能量分辨竞争碰撞诱导解离方法测量了甲醇、乙醇、2-丙醇和2-甲基-2-丙醇等一系列醇类化合物的气相酸度。本文用导向离子束串联质谱仪研究了氟化物-醇、[F-.HOR]、醇盐-水、[RO-.HOH]和醇盐-甲醇[RO-. HOCH_3]质子结合复合物的竞争解离反应。的反应截面和产物的分支分数的两个质子转移通道测量作为碰撞能量的函数。两个产物通道之间的焓差是通过使用RRKM理论对阈值附近的反应横截面进行建模来发现的，以考虑能量依赖的产物分支比和动力学位移。从焓差，确定相对于HF和H2O的众所周知的值的醇气相酸度。测得的气相酸度为Δ（酸）H（298）（CH 3OH）= 1599 +/- 3 kJ/mol、Δ（酸）H（298）（CH 3CH 2 OH）= 1586 +/- 5 kJ/mol、Δ（酸）H（298）（（CH 3）（2）CHOH）= 1576 +/- 4 kJ/mol和Δ（酸）H（298）（（CH 3）（3）COH）= 1573 +/- 3 kJ/mol。
Energy-resolved competitive collision-induced dissociation methods are used to measure the gas-phase acidities of a series of alcohols (methanol, ethanol, 2-propanol, and 2-methyl-2-propanol). The competitive dissociation reactions of fluoride-alcohol, [F-.HOR], alkoxide-water, [RO-.HOH], and alkoxide-methanol [RO-.HOCH3] proton-bound complexes are studied using a guided ion beam tandem mass spectrometer. The reaction cross sections and product branching fractions to the two proton transfer channels are measured as a function of collision energy. The enthalpy difference between the two product channels is found by modeling the reaction cross sections near threshold using RRKM theory to account for the energy-dependent product branching ratio and kinetic shift. From the enthalpy difference, the alcohol gas-phase acidities are determined relative to the well-known values of HF and H2O. The measured gas-phase acidities are Delta(acid)H(298)(CH3OH) = 1599 +/- 3 kJ/mol, Delta(acid)H(298)(CH3CH2OH) = 1586 +/- 5 kJ/mol, Delta(acid)H(298)((CH3)(2)CHOH) = 1576 +/- 4 kJ/mol, and Delta(acid)H(298)((CH3)(3)COH) = 1573 +/- 3 kJ/mol.