So PI bonds have electron density both above and below the bond axis, but they actually have a nodal plane at this z, this bond axis here.

键在键轴之上，和之下都有电子密度，但它们在z方向有节面，这是键轴的地方。

youdao

We want to discuss sigma bonds and pi bonds.

我们要讨论sigma键和π键。

youdao

So let's think about how we can classify single and double and triple bonds, which is what we're really used to dealing with in terms of these sigma bonds and these pi bonds.

让我们想想怎么来分类单键双键,和三键，这在我们在考虑sigma键,和π键是很有用的。

youdao

So, what we end up having is three of these pi -- 2 p y 2 p y bonds, we can have one between these two carbons here.

我们剩下的有三个π键-,2py2py键，在这两个碳原子之间会有一个。

麻省理工公开课 - 化学原理课程节选