作者:Keshavaraja, Alive、Hegde, Vishnumurthy R.、Pandey, Bipin、Ramaswamy, Arumugamangalam V.、Kumar, Pradeep、Ravindranathan, T.
DOI:——
日期:——
Stereoelectronic effects on acetal cleavage. The separation of the π-donor and σ-acceptor properties of oxygen
作者:Anthony J. Kirby、Robert J. Martin
DOI:10.1039/p29830001633
日期:——
group is controlled by the geometry at the remote acetal centre. The hydrolysis of the cis-axial compound (3ca), in which the remote oxygen atom can act as a π-donor, is up to 200 times faster than that of its trans-isomer (3ta), in which it cannot, but acts simply as a σ-acceptor to slow C–OAr cleavage. The magnitude of the stereoelectroniceffect on ΔH‡ is of the order of 7 kcal (30 kJ) mol–1.
双缩醛(3)的自发的,一般的酸和H 3 O +催化的水解是不寻常的,半连续的碎片,其中4-硝基苯酚酸酯离去基团的损失速率受远端乙缩醛的几何形状控制。中心。顺式(3ca)的化合物(其中远程的氧原子可以充当π-给体)的水解速度比其反式-异构体(3ta)(其不能但可以起作用)的水解速度快200倍只是作为σ受体来减慢C–OAr裂解。立体电子效应对ΔH ‡的大小约为7 kcal(30 kJ)mol –1。