Salpin Jean-Yves, Tortajada Jeanine
Laboratoire Analyse et Environnement, UMR 8587, Bâtiment Maupertuis Université d'Evry Val d'Essonne, Boulevard François Mitterrand, 91025, France.
J Mass Spectrom. 2004 Aug;39(8):930-41. doi: 10.1002/jms.671.
The gas-phase acidity of D-glucopyranose was studied by means of B3LYP calculations combined with 6-31G(d,p) or 6-31+G(d,p) standard basis sets. For each anomer, deprotonation of the various primary and secondary hydroxyl groups was considered. As in solution, the anomeric hydroxyl is found to be the most acidic for both anomers, but only when the 6-31+G(d,p) basis set is used for geometry optimization. Deprotonation of the anomeric hydroxyl induces an important C(1)--O endocyclic bond elongation and subsequently promotes an energetically favored ring-opening process as attested by the very small calculated activation barriers. The results also suggest that interconversion between the various deprotonated alpha- and beta-anomers may easily occur under slightly energetic conditions. B3LYP/6-311+G(2df,2p) calculations led to the an absolute gas-phase acidity of deltaacidGo(298)(alpha-D-glucose) = 1398 kJ mol(-1). This estimate matches well the only experimental value available to date. Finally, this study again confirms that the use of diffuse functions on heavy atoms is necessary to describe anionic systems properly and to achieve good relative and absolute gas-phase acidities.
通过结合6-31G(d,p)或6-31+G(d,p)标准基组的B3LYP计算研究了D-吡喃葡萄糖的气相酸度。对于每种异头物，考虑了各种伯羟基和仲羟基的去质子化。与在溶液中一样，发现异头羟基对于两种异头物都是最酸性的，但仅当使用6-31+G(d,p)基组进行几何优化时才是如此。异头羟基的去质子化导致重要的C(1)--O环内键伸长，并随后促进了能量上有利的开环过程，计算得到的活化能垒非常小就证明了这一点。结果还表明，在稍微高能的条件下，各种去质子化的α-和β-异头物之间的相互转化可能很容易发生。B3LYP/6-311+G(2df,2p)计算得出δacidGo(298)(α-D-葡萄糖) = 1398 kJ mol(-1)的绝对气相酸度。该估计值与迄今为止唯一可用的实验值非常吻合。最后，这项研究再次证实，在重原子上使用弥散函数对于正确描述阴离子体系以及获得良好的相对和绝对气相酸度是必要的。
