Stabilization of Carboxylate Anion with a NH···O Hydrogen Bond: Facilitation of the Deprotonation of Carboxylic Acid by the Neighboring Amide NH Groups
作者:Akira Onoda、Yusuke Yamada、Jiro Takeda、Yoshiki Nakayama、Taka-aki Okamura、Mototsugu Doi、Hitoshi Yamamoto、Norikazu Ueyama
DOI:10.1246/bcsj.77.321
日期:2004.2
weak intramolecular hydrogen bond between the NH and O=C group, and no NH...OH hydrogen bond is formed in the carboxylic acid state. Carboxylate anion 3 forms a strong, intramolecular, partially-covalent hydrogen bond between NH...O - (anion). The strength of the NH...O hydrogen bonds is also maintained in a solution having a low dielectric constant. The pK a values for 1 and 2, measured in a micellar
羧酸的 NH...O 氢键的形成,2,6-(t-BuCONH) 2 C 6 H 3 COOH (1) 和 2-t-BuCONH-6-MeC 6 H 3 COOH (2) , 羧酸盐 [NEt 4 ][2,6-(t-BuCONH) 2 C 6 H 3 COO] (3) 和混合复合物 [N(n-Pr) 4 ][H2,6-( t-BuCONH) 2 C 6 H 3 (COO)} 2 ] (4),通过X-射线结构分析确定。1 H NMR 和 IR 光谱,无论是在固态还是在溶液中。酰胺NH基团在NH和O=C基团之间形成弱分子内氢键,在羧酸状态下不形成NH...OH氢键。羧酸根阴离子 3 在 NH...O -(阴离子)之间形成强的、分子内的、部分共价的氢键。NH...O 氢键的强度在具有低介电常数的溶液中也得以保持。1 和 2 的 pKa 值,在胶束溶液中测量,