物理化学学报 >> 1996, Vol. 12 >> Issue (10): 892-899.doi: 10.3866/PKU.WHXB19961007

研究论文 上一篇    下一篇

气相质子转移反应中热化学和动力学的关系

冯万勇   

  1. 美国俄亥俄州立大学化学系，哥伦布 43210-1173
  • 收稿日期:1996-02-09 修回日期:1996-06-10 发布日期:1996-10-15
  • 通讯作者: 冯万勇

The Correlation between Thermochemistry and Kinetics in the Proton Transfer Reactions of Small Proton Bound Clusters

Feng Wan-Yong   

  1. Department of Chemistry,The Ohio State University,Columbus,OH 43210-1173,U.S.A
  • Received:1996-02-09 Revised:1996-06-10 Published:1996-10-15
  • Contact: Feng Wan-Yong

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摘要：

质子键合的分子簇的离子－分子反应中的热化学和动力学关系的考察结果表明：对于非烷基锁闭的分子簇，如（C2H5OH）nH＋（n＝1-3）和（CH3OH）3H＋；与中性碱B的质子转移反应，属快速反应，其反应效率γ是由总反应的自由能变化△γGm控制，而与反应过渡态的本质无关. 那些反应可能存在两个中间体，因电子转移导致质子从分子簇内部转移到中性碱，进而导致二个或三个溶剂分子的直接蒸发；烷基锁闭的质子键合的二聚体，如（CH3CN）2H＋，（CH3OCH3）2H＋，（CH3COCH3）2H＋和（C3COOCH3）2H＋，与中性碱的质子转移反应，其效率远小于1, 与总反应的△γGm无关.

关键词: 质子键合的分子簇, 离子-分子反应, 反应效率r, 总反应的自由能变化ΔrGm

Abstract:

 The correlation between thermochemistry and kinetics in the proton transfer reactions of small proton bound clusters has been examined. The results show that these reactions with some neutral bases for thee non-alkyl blocked proton bound clusters such as (C2H5OH)nH+(n=1-3) and (CH3OH)3H+ are intrinscally fast. The reactivity efficienices are controlled by overall reaction free energy changes or equilibrium constants, rather than inhibited by the nature of transition state. Reaction entropy changes have the significant influence on reaction kinetics. A proton switch from the ionic center to the periphery between two intermediates, resulting in the evaporation directly of two or three solvent molecules, is proposed for the reactions of dimers and trimers. The reactivity efficiencies for the alkyl blocked dimers such as (CH3CN)2H+,(CH3OCH3)2H+,(CH3COCH3)2H+ and (CH3COOCH3)2H+ are very low, These reactions are not controlled by overall reaction free changes or equilibrium constants.

Key words: Proton bound cluster, Ion-molecule reaction, Reactivity efficiency, Overall reaction free energy changes ΔrGm