How did ring formation occur here?

#1

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 ?

Thanks.

#2

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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#3

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

#4

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#5

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

#6

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.

#7

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

#8

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

#9

Oh, I understood now.
Thanks !

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#10

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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#11

Can you show me the major product of this question.

#12

The major product isn't mentioned.

#13

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.

#14

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

#15

No this can be the product

#16

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

Thanks :grinning:

#17

Now you got it,Feel free to ask