So that's exactly what our definition of a pi bond is, so we have one sigma bond, and one pi bond. 这是我们对π键的定义,我们有一个sigma键,和一个π键。
So would you expect this to be a pi bond or a sigma bond her PROFESSOR: OK, so I'm hearing some mixed answers. 你们觉得这是一个π键还是sigma键?,我听到有不同的答案。
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。
But once you have a double bond here, we have our pi bond, as well as our sigma bond. 但一旦你有了双键,我们有π键,也有sigma键。
So we can kind of flip it this way this will be one pi bond, this will be another interacting between these p orbitals. 我们可以把它这样翻一下,这是一个π键,这是另外一个p轨道之间,相互作用的π键。
And so both of these lobes together constitute a pi bond. 上下两片叶一起组成了一根π键。
So in order to rotate a double bond, you have to actually break the pi bond, so essentially what you're doing is breaking the double bond. 为了能够旋转双键,你必须打破一个π键,本质上我们要做的就是打破双键。
Now let's think about this first pi bond, which will be above and below the bonding axis. 让我们先来看这个π键,它在键轴的上面和下面。
So if I try to rotate my2 atoms, you see that I have to break that pi bond, because they need to be lined up so that the electron density can overlap. 如果我要试着转动两个原子,你会看到我必须要打破一个π键,因为他们需要连接起来,让那些电子能够重叠。
So, as they're very quietly handing out your class notes, let's think about what this bond is here, this boxed bond, is it a pi bond or a sigma bond? 在他们发讲义的同时,我们来看看这个键,方框里的这个键,它是sigma键还是π键?
Pi orbitals are a molecular orbital that have a nodal plane through the bond axis. 轨道是沿着键轴,有节面的分子轨道。
Poly ( ether imide)( PEI) is a modification kind of high performance polymer, which adds a ether bond to macromolecular chain of polyimide ( PI). 聚醚酰亚胺(PEI)是在聚酰亚胺(PI)链上引入醚键形成的一类高聚物。
So if we have a single bond here, would you consider that a sigma bond or a pi bond? 如果这里有个单键,你觉得这是sigma键还是π键?
So our second bond is going to be a pi bond. 第二个键是π键。
So it's very important to be keeping in mind that any time you see a double bond, you have a pi bond there, so you're not going to see any rotation around the bond axis. 所以你们要记住,任何时候你们看到一个双键,这里面有π键,你们不会看到关于键轴的任何转动。
We're already using it up in this pi bond here, so that means we're limited to only two other spots on the molecule, so we have three. 我们已经把它用到这个π键里去了,所以这意味着,我们在分子里只剩下两个位置,所以一共是三个。
Is that a sigma or a pi bond? 这是sigma键还是π键?
Nano-particles of SiO2 form the hydrogen bond with carbonyl of PI, which changes the geometrical and electronic structure of PI, but the bond order changes a little. SiO2纳米颗粒与PI上的羰基形成氢键,使得PI的几何结构和电子结构发生了变化,但键级基本没有变化。