来自《耶鲁大学开放课程：新生有机化学 第6集 第6集》

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  But notice that it's as if the carbons formed bent bonds.
  看上去碳碳之间形成的是弯曲的键
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  So the bonds from those central carbons at the end
  所以两边的碳碳键
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  go up and down,
  垂直于平面向上和向下
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  but the ones in the middle are in- plane.
  而中间的键在平面内
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  Now how many electrons are there in a bond?
  那一个键内有多少个电子呢
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  So here we're going to plot how many electrons vertically,
  在这张图上 我们用纵轴表示电子数
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  and how long the bond is,
  横轴表示键长
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  which is related to whether it's single, double, triple.
  分别对应单键 双键 和三键
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  In fact, a single bond is there;
  单键在这
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  a double bond and a triple bond have those distances.
  双键和三键的键长要短一些
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  Now if you--and in fact you
  其实
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  could also do a one-and-a- and a half bond,
  你也可以加上1.5键