How did ring formation occur here?


In question 99 shouldn't there be electrophilic addition on the double bond followed by SNi type addition of OH group ?

The answer is given as (C). I don't know how did the ring form. Can anyone tell me how did it form ?



H+ from H3PO3 protonated OH and gives a OH2+ there which is removed forming a carbonation and undergoes rearrangement to a 3° C+ at the end, then C+ attacks the double bond and HPO4- extracts H from the andject carbon to the new formed C+

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Can you post the solution with the mechanism. I didn't understand that well.


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Thanks, but I have a doubt.

Can carbocation take part in electrophilic addition reaction ? I know it is an electrophile but I thought only H-X type compounds which give an electrophilic proton can take part in electrophilic addition


Also why didn't electrophilic addition by H+ occur first on alkene ? As the π bond of alkene is weak it could be easily broken while the sigma bond of C-O is stronger.


See carboncation will take part in electrophilic addition reaction when there is a more stable product is forming.
Still have doubts you can ask.


Your are right but in this question electron density on O is more than alkene. That why H(+) will attack on O-H first .


Oh, I understood now.
Thanks !

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I just referred to LG Wade and a similar question was mentioned with H3PO4 replaced by H2SO4. There it is mentioned that the cyclic product is a minor product.

Now how could we answer this question if it isn't mentioned that we need to give only the minor product ?

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Can you show me the major product of this question.


The major product isn't mentioned.


See No other products has given for this question except minor product . We will see the best possibility, we have to go with our concept and the concept is that ring product is more stable.


The product mentioned in option (d) could also be possible right ?


No this can be the product


Oh yes, sorry. I shifted the methyl in the wrong way.

Thanks :grinning:


Now you got it,Feel free to ask