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Organic Chemistry

Blazing goIITian

Joined:	1 Nov 2008
Post:	329

10 Apr 2009 00:06:27 IST

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256

IIT 2008 ...Doubt in Question

None

IITJEE 2008 :

STATEMENT-1: Bromobenzene upon reaction with Br2/Fe gives 1, 4 – dibromobenzene as the major product.
and
STATEMENT-2: In bromobenzene, the inductive effect of the bromo group is more dominant than the
mesomeric effect in directing the incoming electrophile.

(A) STATEMENT-1 is True, STATEMENT-2 is True; STATEMENT-2 is correct explanation for STATEMENT-1
(B) STATEMENT-1 is True, STATEMENT-2 is True; STATEMENT-2 is NOT a correct explanation for
STATEMENT-1
(C) STATEMENT-1 is True, STATEMENT-2 is False
(D) STATEMENT-1 is False, STATEMENT-2 is True

Sol. (C)
In bromobenzene, it is the mesomeric effect which directs the incoming electrophile. I thought that for halogens, the inductive effect dominated ?? ...Also , can someone please elaborate on the function of Br2/Fe

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Comments (3)

Siddhartha Gupta

Blazing goIITian

Joined: 1 Nov 2008

Posts: 329

11 Apr 2009 09:25:55 IST

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Pls answer .. .. ..

pranav agrawal

Blazing goIITian

Joined: 24 Sep 2008

Posts: 1694

11 Apr 2009 09:50:22 IST

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in Br , it has + m and -I effect ~~

statement 1 is correct ~~

statement 2 is wrong ~~

this concept is one of the most confusing one ~ so therefore it is an IIT question ~~ ha ha ha :D

lemme try.... took me loads of book to read to get this ~~~

it is true that the -I effect of the Br group is more than the + R effect . so, there is net deactivation. but +R effect, to some extent, opposes this deactivation at o and p position~~ so reaction occurs at o- p- position ~~

hence concluded, in bromobenzene, the orientation of the electrophile is decided by "weak" resonance effect and reactivity by "strong" -I effect ~~

so statement 2 saying that "In bromobenzene, the inductive effect of the bromo group is more dominant than the
mesomeric effect in directing the incoming electrophile." is wrong because it is resonance effect that direcs the incoming electrophile ~~

and about Br2/Fe, it produces Br+ electrophile which attacks on electron benzene ring ~~

hope it helps ~~

Siddhartha Gupta

Blazing goIITian

Joined: 1 Nov 2008

Posts: 329

11 Apr 2009 13:56:15 IST

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Thx a lot Mate .... u are the most helpful guy I've come across on this site .... :D ..... & you've also got a good chance tomorrow of cracking JEE .... Best of luck PS . could u please stop the deadline in your signature ...its making me nervous now .

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