交大附中闵行分校   徐爱明

THE INSPIRATION OF A DREAM

                  ——August Kekulé

    I was sitting writing at my textbook, but the work did not progress; my thoughts

were elsewhere. I turned my chair to the fire, and dozed. Again the atoms were

gamboling before my eyes. This time the smaller groups kept modestly in the

background. My mental eye, rendered more acute by repeated visions of this kind,

could now distinguish larger structures of manifold conformations; long rows,

sometimes more closely fitted together; all twisting and turning in snake-like motion.

But look! What was that? One of the snakes had seized hold of its own tail, and the

form whirled mockingly before my eyes.  As if by a flash of lightning. I woke..…

I spent the rest of the night working out the consequences of the hypothesis.

    Let’s learn to dream, gentlemen, and then perhaps we shall learn the truth.

“Chances always visit the prepared brain”

1865年6月，凯库勒向伦敦皇家学会递交的报告中，凯库勒提出了三点假设：

（1）苯的六个碳原子形成闭合环状，即平面六边形

（2）各碳原子间存在着单、双键交替形式

（3）每个碳原子均连接一个氢原子

简写成：

分子中环内的留个碳原子之间单双建并不存在，凯库勒认为是共振 形成了结余单键与双肩之间的大π键。

借助扫描隧道显微镜和实验证据，

知道了苯分子中键角都是120 °、

碳—碳键长都相等、

成键后的苯分子呈现平面结构：

苯的比例模型

苯的性质介于烷烃和烯烃之间。

1、苯的加成反应：

2、取代反应

  （1）苯的卤代：

       苯的溴代

实验改进：

（2）苯的硝化反应

     苯的硝化反应

思考：

1、苯的结构是像烷烃还是烯烃？

2、苯的性质是像烷烃还是烯烃？

       具体表现在哪些方面？

3、苯的同系物应该含有什么结构？

       分子组成上与苯有什么差异？