Ben-Ari Julius, Etinger Alex, Weisz Adrian, Mandelbaum Asher
Department of Chemistry, Lise Meitner-Minerva Center for Computational Quantum Chemistry, Technion-Israel Institute of Technology, 32000 Haifa, Israel.
J Mass Spectrom. 2005 Aug;40(8):1064-71. doi: 10.1002/jms.881.
The isomeric 3- and 4-dehydrobenzenesulfonic acid anions b and c were prepared by collision induced dissociation (CID) of the M - H ions of isomeric sulfobenzoic acids obtained by negative electrospray ionization (ESI). The CID spectra (MS(3)) of anions b and c are different from each other, and both are different from that of the isomeric benzenesulfonate anion a, obtained from benzenesulfonic acid. The stability of ions b and c shows that 1,2-proton transfer does not take place in this system under the conditions of the CID experiment. Density functional (DFT) calculations at B3LYP/6-31+G(2d,p) level of theory show that benzenesulfonate anion a is the most stable isomer, and the energies of isomers b and c are higher by more than 65 kcal mol(-1). The calculated energies of the transition states involved in the 1,2-hydrogen migration leading to the interconversion of the isomeric anions are very high (>120 kcal mol(-1)relative to ion a, barrier energies >55 kcal mol(-1)), much higher than those of transition structures leading to fragmentation. This situation does not allow isomerization of ions b and c to a, under the conditions of the CID experiments. The isomeric 2-dehydrobenzenesulfonic acid anion isomerizes to the benzenesulfonate anion a by a facile proton transfer from the SO(3)H group to the adjacent position 2. The results of this work indicate that the gas phase deprotonation of meta- and para-sulfobenzoic acids is a kinetically controlled process.
通过对经负电喷雾电离（ESI）得到的异构磺酸苯甲酸的M - H离子进行碰撞诱导解离（CID），制备了异构的3 - 和4 - 脱氢苯磺酸阴离子b和c。阴离子b和c的CID谱（MS(3)）彼此不同，且均与由苯磺酸得到的异构苯磺酸根阴离子a的CID谱不同。离子b和c的稳定性表明，在CID实验条件下，该体系中不会发生1,2 - 质子转移。在B3LYP/6 - 31 + G(2d,p)理论水平下的密度泛函（DFT）计算表明，苯磺酸根阴离子a是最稳定的异构体，异构体b和c的能量比其高65 kcal mol(-1)以上。计算得出的导致异构阴离子相互转化的1,2 - 氢迁移所涉及的过渡态能量非常高（相对于离子a >120 kcal mol(-1)，势垒能量>55 kcal mol(-1)），远高于导致碎片化的过渡结构的能量。这种情况使得在CID实验条件下，离子b和c无法异构化为a。异构的2 - 脱氢苯磺酸阴离子通过从SO(3)H基团向相邻的2位进行质子转移，异构化为苯磺酸根阴离子a。这项工作的结果表明，间位和对位磺酸苯甲酸的气相去质子化是一个动力学控制的过程。
