corresponding reactions with benzylamine (k BzNH2) has revealed that quinuclidine is less reactive than benzylamine toward 3a–3i although the former is 2.1 pK a units more basic than the latter. Steric hindrance exerted by quinuclidine has been suggested to be responsible for the decreased reactivity of the tertiary amine. The Brønsted‐type plot for the reactions of 3a–3i with quinuclidine is linear with
用分光光度法测定了O- Y取代的苯基
硫代苯甲酸酯(3a-3i)与
奎尼丁的反应的二级速率常数(k quin)。将k quin与先前报道的与
苄胺(k BzNH2)进行的相应反应的速率常数进行比较后发现,
奎尼丁对3a-3i的反应性比
苄胺低,尽管前者比后者的碱性高2.1 p K a单位。有人建议
奎尼丁施加的立体阻碍是造成叔胺反应性降低的原因。Brønsted型图的反应 3a–3i与
奎尼丁成线性关系,βlg = −0.37。与常数相关的哈米特图显示出许多分散点(R 2 = 0.982)。与此相反,汤川-津野情节导致极好的线性相关性(- [R 2 = 0.9992)与ρ Ŷ = 0.96和- [R = 0.51,表明负电荷部分地开发上的离去基团的O原子。因此,已经得出结论3a-3i与
奎尼丁的反应是通过协同机制进行的,在该机制中,在决定速率的过渡态中,离去基团的排出仅提前了一点。