为何弱离去基团羟基在Aldol反应产物中就容易离去  

Why Does the Weak Leaving Group Hydroxyl in Products of the Aldol Condensation Leave Easily

作　　者：许家喜 麻远[2] XU Jia-Xi;MA Yuan(College of Chemistry,Beijing University of Chemical Technology,Beijing 100029,China;Department of Chemistry,Tsinghua University,Beijing 100084,China)

机构地区：[1]北京化工大学化学学院,北京100029 [2]清华大学化学系,北京100084

出　　处：《化学教育（中英文）》2024年第4期121-123,共3页Chinese Journal of Chemical Education

基　　金：有机化学本科育人团队项目;有机化学和中级有机化学一流课程建设项目。

摘　　要：醇中的羟基是很弱的离去基团,一般需要通过用质子酸质子化、与路易斯酸络合或者形成磺酸酯后才容易离去;β-位无吸电子取代基的醇,在碱性条件下难以直接离去。而Aldol反应的产物β-羟基醛酮,在碱性条件下就可以实现羟基的离去,脱水生成α,β-不饱和醛酮。这种醇脱水反应条件的不寻常会引起学生困惑。通过分析2类反应的机理和反应过程中立体电子效应的不同,合理地解释了这2类醇脱水反应的差别,加深了学生的理解。The hydroxyl group in alcohols is a weak leaving group.It can leave easily only after protonation with acids or formation of complexes with Lewis acids,or transformation into their sulfonates.It cannot depart under basic conditions.However,β-hydroxyaldehydes and ketones,the products of the Aldol condensation,can leave their hydroxyl group to realize dehydration under basic conditions,generatingα,β-unsaturated aldehydes and ketones.These differences in dehydration of alcohols frequently cause students’confusion.This article rationally explains the differences of these two classes of dehydrations of alcohols through analyses of their reaction mechanisms and stereoelectronic effect in the dehydrations(eliminations).It would provide a deeper understanding for students.

关 键 词：醇 羟基 脱水 消除 碱性条件 

分 类 号：G642[文化科学—高等教育学] O621.25-4[文化科学—教育学]