The relative importance of ground-state conformation and orbital orientation in intramolecular catalysis: hydrolysis of aryl hydrogen biphenyl-2,2′-dicarboxylates
作者:Ramamurthy Chandrasekar、Nagaswami Venkatasubramanian
DOI:10.1039/p29830000421
日期:——
The pH-rate profile for the hydrolysis of 4-nitrophenyl hydrogen biphenyl-2,2′-dicarboxylate (diphenate) shows a pH-independent region in the pH range 5–9, and obeys rate law (i). Compared with 4-nitro-kobs=kaaH//Ka+aH+Kw//aH·kOH+kbKa//Ka+aH(i) phenyl benzoate, the hydrolysis of 4-nitrophenyl hydrogen diphenate proceeds 800 times faster at pH 6.0. This is explained by invoking intramolecular nucleophilic
水解4-硝基苯基氢联苯-2,2'-二羧酸盐(苯甲酸酯)的pH速率分布图显示pH范围为5-9的非pH依赖区域,并遵守速率定律(i)。与4-硝基-k obs = k a相比a H // K a + a H+K w // a H· k OH + k bK a // K a + a H(i)苯甲酸苯酯,在pH 6.0时,4-硝基苯二氢苯酚的水解进行得快800倍。这可以通过相邻的羧酸根离子进行分子内亲核催化来解释。在pH 6.0(k H 2 O / k D 2 O 1.22)和低的活化负熵(-7.2 cal K –1 mol –1),哈米特反应常数的高值(ρ2.19 )时,溶剂同位素的影响可忽略不计)和离去基团变化的布朗斯台德常数(β–0.95)为亲核催化提供了证据。已经计算出4-硝基苯基联苯氢酸分子内环化的有效摩尔摩尔数约为1。200,与在戊二酸酯中观察到的该现象相近,并且与琥珀酸所获得的相比非常