Decarboxylation of cyclohex-1-ene-1,2-dicarboxylic acid by electrolysis method


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> What is the major product when cyclohex-1-ene-1,2-dicarboxylic acid is electrolysed?
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My try:


[![enter image description here](https://i.stack.imgur.com/hZfQt.jpg)](https://i.stack.imgur.com/hZfQt.jpg)


I got 2 cases but I am unable to decide which product is major, and need help here.




Turns out a similar reaction has been performed, the reaction proceeds via the following mechanism



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> ![enter image description here](https://i.stack.imgur.com/5uHxb.jpg)  
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> [SOURCE](https://books.google.co.in/books?id=t63ILJENEH8C&pg=PA17&lpg=PA17&dq=1,2,3,4,5,6,7,8-octahydrobiphenylene&source=bl&ots=pxCLDMZpsZ&sig=YRzhqBkBTglL81rYFLi8Za_trsw&hl=en&sa=X&ved=2ahUKEwid5tmQ3_jZAhVEJ5QKHW5dAa8Q6AEwDXoECAcQAQ#v=onepage&q=1%2C2%2C3%2C4%2C5%2C6%2C7%2C8-octahydrobiphenylene&f=false) 
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The cyclohexyne dimerizes to 1,2,3,4,5,6,7,8-octahydrobiphenylene. Then further rearranges. So I would say that electrolysis is feasible with rearrangement as depicted in the picture .  

 The second compound(1,2,3,4,5,6,7,8-octahydrobiphenylene) which you've drawn is more stable since very unstable compounds (cyclohexyne) do not form even more unstable compounds. The second compound will not be the final product/major product owing to its high instability due to anti aromaticity.




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**PS**  

 I haven't delved into the details regarding the instability of cyclohexyne and 1,2,3,4,5,6,7,8-octahydrobiphenylene since they have been well covered in Gaurang's answer


 6

From [Wikipedia](https://en.wikipedia.org/wiki/Cycloalkyne),



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> Cyclooctyne ($\ce{C8H12}$) is the smallest cycloalkyne capable of being isolated and stored as a stable compound
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This is because, again quoting the simple language:



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> Because of the linear nature of the $\ce{C–C≡C–C}$ alkyne unit, cycloalkynes can be highly strained and **can only exist when the number of carbon atoms in the ring is great enough to provide the flexibility** necessary to accommodate this geometry. (self-emphasis)
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Hence, your case I is invalidated. 


Regarding case II, the middle four-member ring has $\ce{4\pi}$ electrons in conjugation in a planar system. By Hückel's rule, this ring will be **anti-aromatic**, and therefore, will not exist. 


Therefore, we can say that both the cases are not favorable. 




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**Correction**: I initially mentioned that the electrolysis is probably unfavorable, both due to the theoretically unfavorable molecules I and II, and a lack of favorable research data on Google Scholar for "electrolysis of "cyclohexene-1,2-dicarboxylic acid"" or "decarboxylation of "cyclohexene-1,2-dicarboxylic acid"". However, [Avnish's answer](https://chemistry.stackexchange.com/a/93644/5026) demonstrates dimerization of cyclohexyne to a more stable form, though not exactly obtained from electrolysis, but which seems very plausible. So, I am compelled to say - at least with this much data - that the electrolysis seems favorable.  

With that said, however, case I and II are certainly still not the major products (not even minor).


 5

Without data on the actual products, no serious prediction can be made. Therefore I will make a wild guess:


The diradical, if it formed would be vinylic: very reactive. It would abstract hydrogen atoms from allylic positions of the unreacted cyclic diacid dianion so the first product would be 1,3-cyclohexadiene.


More likely, the electrolysis would produce a monoradical which would pick up a single hydrogen to give cyclohexene 1-carboxylic acid as a first product. If this became the major product and was decarboxylated in a second step, it would also give 1,3-cyclohexadiene.


However, with radicals being formed from a starting material that has allylic hydrogens, I predict that the major product will be tar. Poly-tar.


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