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So let's have a clicker question here on how many total pi bonds do you expect to see in benzene?
让我们来做个课堂习题,你们觉得苯环里有一共多少个π键？
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But, of course, what you saw in recitation, and hopefully, what you can now think very quickly by looking at this, is that this is not the only configuration of pi bonds that we could have in benzene.
当然，你们在习题课看到过，你们通过看这个可以很快的想到，这不是苯环里,唯一的π键构型。
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Once you've got that, you can do minus 7 times a vector Just take the vector, multiply it by Pi and flip it over.
明白这点之后,你就可以计算-7乘以矢量,只需用 π 去乘以那个矢量,然后将其方向调转
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These are the ones that are coming right out at you, so this is going to be on a second pi orbital.
它们朝向你们，所以这里有另一个π键。
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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。
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So if I try to rotate my 2 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。
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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。
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And we can simplify this expression as saying negative e squared over 4 pi, epsilon nought r squared. Epsilon nought is a constant, it's something you might see in physics as well.
也会遇到它,在这里，你可以就把它,理解为一个转换系数,我们需要做的。
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How many pi bonds would you expe PROFESSOR: Two, great.
你们预计它有几个π键,两个，很好。
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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。
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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？
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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。
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And the pi star orbitals result from any time you have destructive py interference from 2 p orbitals that are either the p x or the p y.
星轨道是由于2p轨道的相消干涉,不管是px还是。
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Another thing I want to point out about every sigma orbital that you see, and it will make more sense when we contrast it with pi orbitals later.
另外一个我要指出的事情就是,关于每个sigma轨道你能看到,当我们把它和π轨道对比的时候会看的更清楚。
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You can see that we have two unpaired electrons in this molecule here one in the pi 2 p x star, and one in the pi 2 p y star orbital.
你们可以看到我们这个,分子力有两个未配对电子,一个在π2px星，一个在π2py星轨道。
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Do you predict that this will be a sigma or a pi orbital?
你们认为这是sigma轨道还是π轨道？
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