Br2 addition to penten?

[Dencology]

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guys,
is addition of Br2 to 2-pentene is trans or cis? i am 99% that it is trans.

 

[jdent]

YOur 100% right!

 

[topdent1]

guys,
is addition of Br2 to 2-pentene is trans or cis? i am 99% that it is trans.

I would say trans because it first forms the triangle with the Br at the vertex and then the other Br comes in from below and that's how you get trans.

 

[Dencology]

thanks guys.

 

[Mista E]

yup the Br2 for a bromonium ion then splits trans

 

[PreDent2009]

The addition of Br2 to 2-pentene is an ANTI addition that will afford two new chiral centers. The final product 2,3 dibromopentane is an alkane and therefore cannot be considered cis or trans. The addition of 1 mole of Br2 to an alkyne will generate the trans product as the major one. I think you are just getting your nomenclature and chemistry language a little twisted. You don't get trans or cis addition, you get anti or syn addition, which then can lead to either trans or cis, meso, or enantiomeric racemix mixtures.

guys,
is addition of Br2 to 2-pentene is trans or cis? i am 99% that it is trans.

 

[Optimism Smiles]

The addition of Br2 to 2-pentene is an ANTI addition that will afford two new chiral centers. The final product 2,3 dibromopentane is an alkane and therefore cannot be considered cis or trans. The addition of 1 mole of Br2 to an alkyne will generate the trans product as the major one. I think you are just getting your nomenclature and chemistry language a little twisted. You don't get trans or cis addition, you get anti or syn addition, which then can lead to either trans or cis, meso, or enantiomeric racemix mixtures.

Right on! How I remember it: With Br2, one of the Br's looks like it is forming an epoxide, but instead of an "o" at the top of the triangle, you get the Br (a halonium ion that forms a positive charge on Br). Now imagine using the other Br to do like a ring-opening of an epoxide where the Br attacks one carbon (on the bottom since the halonium ion is hindering the top) and the bond from that C to the other Br (which is on top) breaks so you get anti addition. Hope that wasn't confusing.

 

[Dencology]

great. guys. so we never get a syn addition with one mole of Br2.

 

[Contach]

guys,
is addition of Br2 to 2-pentene is trans or cis? i am 99% that it is trans.

addition of Br2 to 2-pentyne is trans.

 

[condoleezarice]

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