Gas phase basicities and relative proton affinities of compounds between water and ammonia from pulsed ion cyclotron resonance thermal equilibriums measurements
作者:J. F. Wolf、R. H. Staley、I. Koppel、M. Taagepera、R. T. McIver、J. L. Beauchamp、R. W. Taft
DOI:10.1021/ja00458a032
日期:1977.8
indicate that protonation is thermodynamically favored in the gas phase at the carbonyl oxygen of the latter. Large effects of polar electronegative substituents have been observed for various oxygen and nitrogen bases. An evaluation of entropy effects in gas phase proton transfer equilibria shows such effects to bemore » generally small for simple bases and approximately equal to entropy effects expected
用于精确测定质子转移平衡常数的脉冲离子回旋共振方法已应用于 46 种碳、氮、氧、磷、硫、砷和硒碱,重复重叠序列,获得水和氨的相对质子亲和力. 在可能进行比较的情况下,结果通常与高压质谱法获得的结果一致。结果为分子结构对基础强度的内在影响提供了重要的新见解。说明了这些结果在导出其他气态离子热化学数据中的应用。特别是,甲基取代基对质子亲和力的影响已被广泛评估,并解释了与 n 碱共轭酸的均裂键解离能的相应影响和取代甲基阳离子的氢化物亲和力的比较。正烷基取代基对水和醇与羧酸及其酯的质子亲和力影响的比较表明,质子化在气相中在后者的羰基氧处是热力学有利的。对于各种氧和氮碱,已经观察到极性电负性取代基的巨大影响。对气相质子转移平衡中的熵效应的评估表明,这种效应对于简单的碱基通常较小,大约等于分子旋转对称数变化时预期的熵效应。最后,目前的结果为评估绝对质子亲和力和相对离子溶剂化能提供了基础。« 更少