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    Hi Everyone,

    So I'm trying to work this out and I'm stumped on how to explain it.

    Basically, when an 8pi system undergoes a thermal electrocyclisation reaction, it's set up a 6pi system. This then undergoes a 6pi thermal electrocyclisation to form a ring junction - a 6membered ring with a 4 membered ring joined to the side. For example:

    http://upload.wikimedia.org/wikipedi...dSynth.svg.png

    But the 4 membered ring is obviously a strained ring. So what is the thermodynamic driving force of this reaction? I've tried typing this into google but I just come up with a lot of academic papers which don't really understand the whys of the reaction. If anyone knows, that would be a huge help!

    Thank you
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    (Original post by maddie91)
    Hi Everyone,

    So I'm trying to work this out and I'm stumped on how to explain it.

    Basically, when an 8pi system undergoes a thermal electrocyclisation reaction, it's set up a 6pi system. This then undergoes a 6pi thermal electrocyclisation to form a ring junction - a 6membered ring with a 4 membered ring joined to the side. For example:

    http://upload.wikimedia.org/wikipedi...dSynth.svg.png

    But the 4 membered ring is obviously a strained ring. So what is the thermodynamic driving force of this reaction? I've tried typing this into google but I just come up with a lot of academic papers which don't really understand the whys of the reaction. If anyone knows, that would be a huge help!

    Thank you
    In this case it would be that you are have a net change of a pi bond --> sigma bond, which is stronger, and evidently offsets the energy increase of the 4 membered ring.

    In reality all pericyclic reactions are reversible, and you have to look at each case on its own to decide where the equilibrium is likely to lie.
 
 
 
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