Quick O Chem Question

[Disinence2]

Hey im trying to help my friend study and i find myself without a book and unable to look up a pretty simple problem.

1,3 butadiene reacted with Br2 over Methanol at -15C. What are the 4 products and what are most stable?

I know one of you out there know! Help me save some time!

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[gotmeds?]

I think you just get a 1,2 and the 1,4 addition. Since you're doing it at low temp (and it's not a radical reaction -- low temp, no light, I assume), you get more of the kinetic product, which is the 1,2. But someone else should check this. I forgot about half of my o-chem the day after the MCAT.

 

[tncekm]

Does it say they are reacted with 1 molar equivalent of Br2 or excess Br2? This makes a difference because its a diene.

 

[Disinence2]

Thanks! I appricaite your help! I forgot half of my O chem the day after the MCAT then unfortunatly the 2nd half after i got my score back.

 

[Disinence2]

Its only 1 Br2 The hint says that each product contains 1 pi bond. Sorry i forgot to include that. But it says they have 4 unique products which is tricking me up, i can only get to.. the 1,2 and 1,4

 

[tncekm]

Sorry, I'm just not seeing it off the top of my head personally, and right now I've got my own ochem to study for But, I can't see four different products unless there is either a ring formation or (the more likely) a resonance structure that is forming two of the minor products. 1,3-butadiene is conjugated so can have resonance.

 

[tncekm]

Oh, I think its just the 1,2-addition and the 1,4-addition but the enantiomers of both. haah That gives 4 products.

 

[swifteagle43]

FOUR PRODUCTS FORM

Product 1
1-bromo-(R) 2butanol
Product 2
1-bromo-(S) 2butanol
Product 3
CIS 1-bromo-4 butanol
Product 4
Trans 1-bromo-4 butanol


The R and S forms(Product 1 & 2) are the most stable. The products of 1,2 addition(Products 1 & 2) take place because the reaction is in cold temperature(hence kinetic).