氨基乙腈的质子化热化学

Protonation thermochemistry of aminoacetonitrile.

作者信息

Bouchoux Guy, Guillemin Jean-Claude, Lemahieu Nadège, McMahon Terrance B

机构信息

Laboratoire des Mécanismes Réactionnels, UMR CNRS 7651, Département de Chimie, Ecole Polytechnique, 91128 Palaiseau Cedex, France.

出版信息

Rapid Commun Mass Spectrom. 2006;20(8):1187-91. doi: 10.1002/rcm.2437.

DOI:10.1002/rcm.2437

PMID:16541413

Abstract

The gas-phase basicity (GB) of aminoacetonitrile (NH2CH2CN, 1) has been determined from measurement of proton transfer equilibrium constants in an ion cyclotron resonance mass spectrometer (GB(1) = 789.3 +/- 1.0 kJ x mol(-1)). Molecular orbital calculations up to the G2 level demonstrate that protonation occurs preferentially on the nitrogen atom of the NH2 group, and provide a theoretical proton affinity (PA(1)) of 824.0 kJ x mol(-1). Exact calculation of the entropy associated with hindered rotations and consideration of Boltzman distribution of conformers allow a theoretical estimate of the molar protonation entropy S degrees (1H+) - S degrees (1) = 8.6 J x mol(-1) x K(-1). Combining this value with experimental GB(1) leads to an 'experimental' proton affinity of 819.2 kJ x mol(-1), in close agreement with the G2 expectation.

摘要

通过在离子回旋共振质谱仪中测量质子转移平衡常数，已确定氨基乙腈（NH₂CH₂CN，1）的气相碱度（GB）（GB(1) = 789.3 ± 1.0 kJ·mol⁻¹）。高达G2水平的分子轨道计算表明，质子化优先发生在NH₂基团的氮原子上，并提供了824.0 kJ·mol⁻¹的理论质子亲和能（PA(1)）。对与受阻旋转相关的熵进行精确计算并考虑构象异构体的玻尔兹曼分布，可对摩尔质子化熵S°(¹H⁺) - S°(1)进行理论估计，其值为8.6 J·mol⁻¹·K⁻¹。将该值与实验测得的GB(1)相结合，得到“实验”质子亲和能为819.2 kJ·mol⁻¹，与G2预期值非常吻合。