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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。
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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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sigma That is one pi orbital. There is one sigma, one pi and there is a second pi, and that is how we are getting the triple bond.
那是一个pi轨道，有一个，一个pi，还有第二个pi轨道，这就是我们如何得到三线态的。
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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。
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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。
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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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So our second bond is going to be a pi bond.
第二个键是π键。
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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。
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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 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。
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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。
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If we have a double bond, we know we need to have only one sigma bond, and we're also going to have one pi bond.
如果我们有双键，我们知道我们需要一个sigma键，还需要一个π键。
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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？
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So it already should make sense why we have that p orbital there, in order to form a pi bond, we're going to need a p orbital.
这里有p轨道是很合理的,为什么我们在这里有P轨道，为了形成一个π键，我们需要一个p轨道。
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In contrast, if we talk about a double bond, what we're now talking about is having both a sigma bond and also one pi bond. And I apologize, I intended to set this up right before class, but that didn't happen today.
相反，如果我们讨论一个双键，我们现在讨论的是,一个sigma键和π键，抱歉，我应该在课前就把这个装好的，今天没装好。
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And again, this is between the p orbitals, these are not hybrid orbitals, so when we name this bond we're going to name it as a pi bond here, because it's between two p orbitals, and it's going to be between the carbon 2 p y orbital, and the other carbon 2 p y orbital.
同样，这是在p轨道之间的，它们不是杂化轨道，所以当我们命名这个键时,我们要命名它为π键，因为它在两个p轨道之间，而且是在碳2py轨道，和另一个碳2py轨道之间。
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So that's two of our types of bonds in benzene, and we have one type left, that's going to actually be the double bond or the pi bond that So we can have one bond here between this carbon's p orbital and this carbon's p orbital.
这就是苯环里的两种键，我们还剩一种，那就是这些p轨道之间，形成的双键或者π键,我们可以在这个碳的p轨道,和这个碳的p轨道之间有个键。
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So even though we see a nodal plane down the center, I just want to really point out that it's only when we have a nodal plane in the internuclear or the bond axis that we're calling that a pi orbital.
虽然在中间有个节面，我想要指出的是,只有节面在核间轴,或者键轴上时,我们才叫它π轨道。
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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。
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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 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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There's not two bonds, that's one pi bond, and the reason is because it's 2 p orbitals coming together, and remember p orbitals have electron density above and below the axis, so when they come together, it kind of looks like one bonds, but essentially what we have here is one pi bond.
这不是两个键，这是一个π键，因为这是两个2p轨道组合而成的，记住p轨道在键轴之上,和键轴之下都有电子密度，当它们靠近时，这看着很像两个键，但本质上它是一个π键。
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Is that a sigma or a pi bond?
这是sigma键还是π键？
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All right, so what we see here is we have our sigma bond that's along the internuclear axis here, but we also have a pi bond, because each of these atoms now has electrons in it's in a p orbital, so we're going to overlap of electron density above and below the bond.
这里我们看到sigma键,是沿着核间轴的，但我们还有一个π键，因为每个原子的p轨道上,都有电子，所以电子密度在键的上面,和下面都有电子密度交叠。
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So in the first case of this first bond here that I've put in a square, what type of a bond is this, is the sigma or pi?
在这第一个键里,我用方框把它标出来了，这个键是什么类型的，sigma还是π？
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