How Does Organic Structure Determine Organic Reactivity? Nucleophilic Substitution and Alkene-Forming Elimination Reactions of α-Carbonyl and α-Thiocarbonyl Substituted Benzyl Derivatives
作者:John P. Richard、Shrong-Shi Lin、Jeanne M. Buccigross、Tina L. Amyes
DOI:10.1021/ja9629064
日期:1996.1.1
The effect of α-(N,N-dimethylcarbamoyl) and α-(N,N-dimethylthiocarbamoyl) substituents on the rate constants for partitioning of α-substituted 1-(4-methoxyphenyl)ethyl carbocations between nucleophilic addition of 50:50 (v:v) MeOH/H2O (ks, s-1) and deprotonation by this solvent (ke, s-1) have been investigated. The data show that these α-amide and α-thioamide substituents result in 80-fold and ≥30 000-fold
α-(N,N-二甲基氨基甲酰基)和α-(N,N-二甲基硫代氨基甲酰基)取代基对α-取代的1-(4-甲氧基苯基)乙基碳正离子在50:50亲核加成之间分配速率常数的影响( v:v) MeOH/H2O (ks, s-1) 和该溶剂的去质子化 (ke, s-1) 已被研究。数据显示,这些 α-酰胺和 α-硫代酰胺取代基分别导致溶剂捕获 4-甲氧基苄基碳正离子的 ks 减少 80 倍和≥30 000 倍,但它们导致的变化要小得多。 ke用于通过溶剂使相应的α-取代的1-(4-甲氧基苯基)乙基碳正离子去质子化。因此,α-硫代酰胺取代基对 α-取代的 1-苯乙基碳正离子在溶剂分解和消除产物的形成之间分配的巨大影响主要是由于该 α-取代基对溶剂捕获碳正离子的 ks 的影响. 实验和计算研究的结果与共同...