IIT JEE , AIEEE Forum - Chemistry , Organic Chemistry

alisha_gupta_27

Identify A

cyclopentene---------------------->A

Br ₂/ hv

waterdemon

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Ans: 1,2 dibromo cyclopentane

nishantsingh89

the product will be trans 1,2 dibromocyclopentane,

in first step Br-Br , bond breaks heterolytically, generating Br+ and Br-

then Br+ attacks the double bond forming cyclic transition state ( Br+ attached to both the carbons involved in double bond)

one of the carbons get electron deficient and it is attacked by Br- from the opposite side

neeraj_agarwal_1990

hey!
doesn't Br2 adds in the presence of CCl4??

in presence of hv, we get allylic substitution.

so product should be 3bromo cyclopent-1-ene.

am i wrong??

ramkumar_november

i think the product is 3-bromo cyclopent-1-ene
because we get only allylic aubstitution..........
allylic free radical is stabilised by resonance.......

what is the right answer??????

waterdemon

3-Bromo cyclopentene is formed when we use NBS in CCl₄
or peroxide

In presence of light , allylic substitution by bromine can
take place only when its concentration is very low.

So both the products can be obtained overhere both trans
1,2,dibromocyclopentane as well as 3-bromocyclopentene

If given that concentration of Br₂ is very low then the
answer given:

3-BromoCyclopentene is right.

Then how can you give the answer when not specified that
what is the concentration of Br₂/Hv.

And you know as per the rules specfied.If nothing such is
specified in the Question then we take the concentration
to be as low.

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nikss

IT WILL B SAME AS IT WOULD B IF U HAVE USED NBS...

ALLYLIC SUBSTITUTION WILL TAKE PLACE...

THE PRODUCT WILL B 3-BROMO-CYCLO PENTENE

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