Matsuda Yoshiyuki, Nakayama Yuichiro, Mikami Naohiko, Fujii Asuka
Department of Chemistry, Graduate School of Science, Tohoku University, Aramaki-Aoba 6-3, Aoba-ku, Sendai, 980-8578, Japan.
Phys Chem Chem Phys. 2014 May 28;16(20):9619-24. doi: 10.1039/c4cp00659c.
Infrared predissociation spectroscopy of the trimethylamine dimer cation generated by the vacuum-ultraviolet photoionization is isomer-selectively carried out by monitoring two main fragment channels, protonated trimethylamine and the trimethylamine monomer cation. The spectral carriers monitored by these two channels are assigned to different isomers of the trimethylamine dimer cation. One is the charge-shared (hemibond) structure, in which the positive charge is intermolecularly delocalized over the dimer through the interaction between the nonbonding orbitals of the nitrogen atoms. In the other isomer, a proton of a methyl group in the ionized moiety is intermolecularly transferred to the nitrogen atom of the neutral moiety and is shared between the carbon and nitrogen atoms. The latter isomer shows that the methyl groups of cationic trimethylamine are highly acidic. This example demonstrates characteristic properties of radical cations with alkyl groups.
通过监测两个主要碎片通道——质子化三甲胺和三甲胺单体阳离子，对由真空紫外光电离产生的三甲胺二聚体阳离子进行红外预解离光谱分析，实现了异构体选择性。这两个通道监测到的光谱载体被归属为三甲胺二聚体阳离子的不同异构体。一种是电荷共享（半键）结构，其中正电荷通过氮原子的非键轨道之间的相互作用在二聚体分子间离域。在另一种异构体中，离子化部分的甲基质子分子间转移至中性部分的氮原子，并在碳和氮原子之间共享。后一种异构体表明阳离子三甲胺的甲基具有高酸性。该例子展示了带有烷基的自由基阳离子的特性。
