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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Gas-Phase Basicities of Acid Anhydrides
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Gas-Phase Basicities of Acid Anhydrides

机译：酸酐的气相碱度

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摘要

The gas-phase proton affinities (PA's) of acetic anhydride, 1, and several representative cyclic anhydrides (succinic, 2; methylsuccinic, 3; glutaric, 4; and 3-methylglutaric, 5) were measured through the use of Fourier transform-ion cyclotron resonance and high-pressure chemical ionization techniques: PA(1) = 844 ± 1 kJ/mol, PA(2) = 797 ± 1 kJ/mol, PA(3) = 807 ± 1 kJ/mol, PA(4) = 816 ± 3 kJ/mol, PA(5) = 820 ± 3 kJ/mol. The results were analyzed in the light of molecular orbital ab initio (MP2/6-31G~*, G2) and density functional theory (B3LYP/6-31G~*) calculations. The enol forms of acetic ahydride and its protonated counterparts were predicted to be significantly less stable than the corresponding diketo conformers. The large proton affinity of acetic anhydride takes its origin from the formation of an intramolecular hydrogen bond in the protonated form. This is supported by the computational results and by the measurement of a sizable entropy loss upon protonation. In contrast, the protonation of cyclic anhydrides is accompanied by an acyl bond fission, thus leading to an entropy gain upon protonation. The protonated structures of cyclic anhydrides are stabilized by an electrostatic attraction between the two opposite parts of the ion. This effect is more pronounced for glutaric derivatives, and this explains the enhancement of the proton affinity observed when the size of the ring increases. It is also related to the increase in entropy of protonation and to the observed methyl substitution effect.
机译：通过使用傅立叶变换离子测量了乙酸酐1和几种代表性的环状酸酐（琥珀酸2，甲基琥珀酸3，戊二酸4和3-甲基戊二酸5）的气相质子亲和力（PA's）。回旋加速器共振和高压化学电离技术：PA（1）= 844±1 kJ / mol，PA（2）= 797±1 kJ / mol，PA（3）= 807±1 kJ / mol，PA（4） = 816±3 kJ / mol，PA（5）= 820±3 kJ / mol。根据分子轨道从头算（MP2 / 6-31G〜*，G2）和密度泛函理论（B3LYP / 6-31G〜*）计算分析结果。乙酸酐和其质子化的对应物的烯醇形式预计比相应的二酮构象异构体稳定程度低得多。乙酸酐的大质子亲和力源自质子化形式的分子内氢键的形成。这由计算结果和质子化后相当大的熵损失的测量所支持。相反，环状酸酐的质子化伴随着酰基键裂变，因此导致质子化时的熵增加。环状酸酐的质子化结构通过离子的两个相对部分之间的静电吸引而得以稳定。对于戊二醛衍生物，这种作用更为明显，这解释了当环的尺寸增加时，所观察到的质子亲和力的增强。它也与质子化熵的增加和观察到的甲基取代作用有关。

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