Chiang Chi-Tung, Shores Kevin S, Freindorf Marek, Furlani Thomas, DeLeon Robert L, Garvey James F
Department of Chemistry, University at Buffalo, State University of New York at Buffalo, Buffalo, New York 14260-3000, USA.
J Phys Chem A. 2008 Nov 20;112(46):11559-65. doi: 10.1021/jp8041186. Epub 2008 Oct 25.
To understand the interaction between toluene and methanol, the chemical reactivity of (C6H5CH3)(CH3OH) n=1-7 cluster ions has been investigated via tandem quadrupole mass spectrometry and through calculations. Collision Induced Dissociation (CID) experiments show that the dissociated intracluster proton transfer reaction from the toluene cation to methanol clusters, forming protonated methanol clusters, only occurs for n = 2-4. For n = 5-7, CID spectra reveal that these larger clusters have to sequentially lose methanol monomers until they reach n = 4 to initiate the deprotonation of the toluene cation. Metastable decay data indicate that for n = 3 and n = 4 (CH3OH)3H(+) is the preferred fragment ion. The calculational results reveal that both the gross proton affinity of the methanol subcluster and the structure of the cluster itself play an important role in driving this proton transfer reaction. When n = 3, the cooperative effect of the methanols in the subcluster provides the most important contribution to allow the intracluster proton transfer reaction to occur with little or no energy barrier. As n >or= 4, the methanol subcluster is able to form ring structures to stabilize the cluster structures so that direct proton transfer is not a favored process. The preferred reaction product, the (CH3OH)3H(+) cluster ion, indicates that this size-restricted reaction is driven by both the proton affinity and the enhanced stability of the resulting product.
为了理解甲苯与甲醇之间的相互作用，通过串联四极杆质谱法并结合计算研究了(C6H5CH3)(CH3OH)n=1 - 7团簇离子的化学反应性。碰撞诱导解离（CID）实验表明，从甲苯阳离子到甲醇团簇的团簇内质子转移反应生成质子化甲醇团簇，仅在n = 2 - 4时发生。对于n = 5 - 7，CID光谱显示这些较大的团簇必须依次失去甲醇单体，直到它们达到n = 4才引发甲苯阳离子的去质子化。亚稳衰变数据表明，对于n = 3和n = 4，(CH3OH)3H(+)是首选的碎片离子。计算结果表明，甲醇子团簇的总质子亲和性以及团簇本身的结构在驱动该质子转移反应中都起着重要作用。当n = 3时，子团簇中甲醇的协同作用为团簇内质子转移反应几乎无能量势垒地发生提供了最重要的贡献。当n≥4时，甲醇子团簇能够形成环状结构以稳定团簇结构，使得直接质子转移不是一个有利的过程。首选的反应产物(CH3OH)3H(+)团簇离子表明，这种尺寸受限的反应是由质子亲和性和所得产物增强的稳定性共同驱动的。
