An electron spin resonance study of the photolysis of carboxylic acids, neat or in non-polar solvents: regiospecific loss of a hydrogen atom from the α-position
作者:John L. Courtneidge、Alwyn G. Davies
DOI:10.1039/p29850000385
日期:——
behaviour of the acids in polar solvents, when they normally show Norrish l cleavage of the alkyl–acyl bond, or photoreduction by the solvent. Two models are considered, to account for the regiospecific formation of the radicals RĊHCO2H. The first assumes that cleavage of a C–OH bond in a hydrogen-bonded dimer yields an HO· radical which is hydrogen-bonded to a carbonyl group of the acid [RCH2C(OH)=O ⋯
当羧酸RCH 2 CO 2 H(R = H,Me,Et或Pr)在纯净或在四氯化碳中被光解时,仅观察到自由基R 2HO 2 H的esr光谱。异丁酸中,Me 2 CHCO 2 H,同样示出了自由基我的频谱2 CCO 2 H在室温下,但在较低温度下自由基我的频谱2 CH·也可以观察到。新戊酸Me 3 CCO 2 H仅显示Me 3的光谱C·自由基。这与酸在极性溶剂中的行为相反,当它们通常显示出Norrish l裂解的烷基-酰基键或被溶剂光还原时。两种模型被认为,以考虑所述区域专一形成自由基的RĊHCO 2 H.第一假定为C-OH键的解理中的氢结合的二聚体产量的HO·基团,其是氢,键合至的羰基酸[RCH 2 C(OH)= O⋯HO˙],然后该物质经历α-H的区域特异性分子内转移。第二个假设是最初形成RCH 2自由基,然后从第二个酸分子中提取氢。