3 ms·

If you want to know a little more about benzene, it is also known as a "Kekule Structure." It is also called a "resonant structure" as the double bonds are sai

by chasil 4y ago

If you want to know a little more about benzene, it is also known as a "Kekule Structure." It is also called a "resonant structure" as the double bonds are said to flip in the ring of carbon atoms. ...or, at least, that was what I heard in high school organic chemistry. That was a very long time ago, and interpretations might have changed. https://en.m.wikipedia.org/wiki/Benzene https://en.m.wikipedia.org/wiki/Benzene

infinite8s 4y ago
They don't exactly flip. It's more like each bond is on average 1.5 electrons. You'll often see it drawn as a hexagon with a small circle in the middle.
jcranmer 4y ago
It's not that the bonds are flipping, but rather that each bond is kind of half a C-C single bond and half a C=C double bond--more of an average 1½ bond. This makes a lot more sense when you start getting into full-blown molecular orbital theory.
- absolutelynobo 4y ago
  aka superposition?
  - moring 4y ago
    That's something I wondered too, but I doubt it. The model used to explain benzene's bonds superficially sounds like superposition, and I can't really speak about the electrons involved (way too complex for me to even imagine), but when you look at the nuclei involved, it sounds implausible that the superposition of irregularly-positioned nuclei results in regularly-positioned nuclei. Implausible because they are too heavy and therefore localized. But that's my layman's knowledge. I'd like to be corrected!
  - jcranmer 4y ago
    I can see why you might think this. It is a quantum mechanical effect, but it has nothing to do with the main quantum mechanical effect everyone knows about (superposition). Superposition of two states is not preserved by measurement: it's more akin to a (complex, not real) probability you'll find the system of one of the states. By contrast, resonant bonds are a real mixing of the two states: you don't observe the carbon-carbon bonds in a benzene molecule as either being a single bond or a double bond, you observe them as a uniform bond that's somewhere between a single bond and a double bond (e.g., bond length). Treating such things as a weighted average of various resonance structures is a usable approximation that allows you to predict the structure of more molecules without having to dive deep into molecular orbital theory.

by chasil 4y ago

infinite8s 4y ago

They don't exactly flip. It's more like each bond is on average 1.5 electrons. You'll often see it drawn as a hexagon with a small circle in the middle.

jcranmer 4y ago

It's not that the bonds are flipping, but rather that each bond is kind of half a C-C single bond and half a C=C double bond--more of an average 1½ bond. This makes a lot more sense when you start getting into full-blown molecular orbital theory.

absolutelynobo 4y ago
aka superposition?
- moring 4y ago
  That's something I wondered too, but I doubt it. The model used to explain benzene's bonds superficially sounds like superposition, and I can't really speak about the electrons involved (way too complex for me to even imagine), but when you look at the nuclei involved, it sounds implausible that the superposition of irregularly-positioned nuclei results in regularly-positioned nuclei. Implausible because they are too heavy and therefore localized. But that's my layman's knowledge. I'd like to be corrected!
- jcranmer 4y ago
  I can see why you might think this. It is a quantum mechanical effect, but it has nothing to do with the main quantum mechanical effect everyone knows about (superposition). Superposition of two states is not preserved by measurement: it's more akin to a (complex, not real) probability you'll find the system of one of the states. By contrast, resonant bonds are a real mixing of the two states: you don't observe the carbon-carbon bonds in a benzene molecule as either being a single bond or a double bond, you observe them as a uniform bond that's somewhere between a single bond and a double bond (e.g., bond length). Treating such things as a weighted average of various resonance structures is a usable approximation that allows you to predict the structure of more molecules without having to dive deep into molecular orbital theory.