[abcc]

i have done an experiment which is the bromination of tran-cinnamic acid .
In theoretically , syn & anti- addition both can occur ;
BUT i only got a anti result , what's the reason?

[abcc]

Brief / revelant explanation is OK
THX

[Dan]

Look up the mechanism, it will become clear.

[abcc]

Look up the mechanism, it will become clear.

i know the mechanism ,
there is bromonium ion formed 
thus ,anti is prefered=)
but i still have a question,
what's the difference between the bromination of trans-anethole and trans-cinnamic acid
why anethole can have syn-addition
actually anethole and cinnamic acid both are quite similar.
Is it because the benzene ring of trans-anethole bond to OCH3,
but trans-cinnamic acid doesn't 
thx

[Dan]

For syn addition to occur, the bromonium ion must be opened (forming a carbocation) so that the bromide can attack the same face as the first bromine. Anethole has a relatively stable carbocation compared to cinnamic acid. Can you see why?

[abcc]

For syn addition to occur, the bromonium ion must be opened (forming a carbocation) so that the bromide can attack the same face as the first bromine. Anethole has a relatively stable carbocation compared to cinnamic acid. Can you see why?

I think the reason for the stable carbocation due to the etherbenzene ring, it has resonnance structures that stabilizes the +ive charge (e- donate), is it  
actually , i am not sure and just guess

[Dan]

I think the reason for the stable carbocation due to the etherbenzene ring, it has resonnance structures that stabilizes the +ive charge (e- donate), is it  
actually , i am not sure and just guess

It's a good guess! Make sure you can draw the resonance structures. This seems like a good explanation to me anyway.

[abcc]

I think the reason for the stable carbocation due to the etherbenzene ring, it has resonnance structures that stabilizes the +ive charge (e- donate), is it  
actually , i am not sure and just guess

It's a good guess! Make sure you can draw the resonance structures. This seems like a good explanation to me anyway.

is my reason possible???
any other reasons are relevant to explain why??
thx

[Dan]

I think it is the reason, again, make sure you can draw the resonance structures.

I can't see any other obvious reasons, but that doesn't mean there aren't any.

[abcc]

I think it is the reason, again, make sure you can draw the resonance structures.

I can't see any other obvious reasons, but that doesn't mean there aren't any.

THE RESONNANC : CH3O=ring=C   
The atom O originally has 2 lone pair e-, thus i think it can donate e- to form double bond and stabilize the +ive charge in the ring
is it the possible structure 

anyway , thx your reply !!