Effect of Alkyl Group Size on the Mechanism of Acid Hydrolyses of Benzaldehyde Acetals
作者:Alexanders T. N. Belarmino、Sandro Froehner、Dino Zanette、João P. S. Farah、Clifford A. Bunton、Laurence S. Romsted
DOI:10.1021/jo0202987
日期:2003.2.1
tertiary acetals, and plots of log k(H) for the H(3)O(+)-catalyzed reaction, (13)C and (1)H chemical shifts, and (1)J(CH) coupling constants against the Charton steric parameter, nu, for alkoxy groups are linear. The second-order rate constant, k(H), increases about 100-fold on going from R = Me to R = t-amyl, indicating the significant role of steric effects on reactivity. Steric effects upon (13)C
当R =甲基,正丁基,但带有仲和叔烷基衍生物,R =异丙基,仲丁基,叔丁基,苯甲醛缩醛PhCH(OR)(2)的水解反应是特定的氢离子催化。叔戊基水解是一般酸催化的。仲和叔烷基的布朗斯泰德α值均在以下范围内:α= 0.57-0.61。开发了一种简单的迭代程序来估算琥珀酸缓冲液的二酸和一酸形式的一般酸催化的各个速率常数。对于仲和叔缩醛,log k(obs)(在[buffer] = 0 M处)相对于pH的图是线性的,对于H(3)O(+)催化的反应,log k(H)的图则是(对于烷氧基而言,13)C和(1)H化学位移以及(1)J(CH)相对于Charton空间参数nu的耦合常数是线性的。二阶速率常数k(H),从R = Me到R =叔戊基时,其增加约100倍,表明空间效应对反应性的重要作用。对(13)C NMR化学位移和偶联常数的立体效应表明,增加烷氧基部分的体积会增加碳反应中心处的电子密度,从而加