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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: ch_wsc on October 17, 2006, 05:33:00 AM

Title: what s the difference between trans and anti stereochemistry ?
Post by: ch_wsc on October 17, 2006, 05:33:00 AM

hi , I am sorry to bother u all with a simple question
I am asked what the stereochemistry of 1,2dibromocyclopentane produced by the reaction of cyclopentene and Br2
I know the 2 bromine atoms will go to opposite sides of 2 carbons but i don't know why it's tran but not anti
thx for any explanation

Title: Re: what s the difference between trans and anti stereochemistry ?
Post by: Albert on October 17, 2006, 06:07:03 AM

When you consider alicyclic compounds, cis means  the substituents are on the same side, while trans isomer has one over and the other under the cyclic structure (http://en.wikipedia.org/wiki/Cis-trans_isomerism).

Anti and syn don't refer to a product but to a reaction (i.e. syn-addition).

Title: Re: what s the difference between trans and anti stereochemistry ?
Post by: movies on October 17, 2006, 08:19:09 PM

Quote from: Albert on October 17, 2006, 06:07:03 AM

Anti and syn don't refer to a product but to a reaction (i.e. syn-addition).

That's not true.  For example, the two diastereomeric products of an aldol reaction are typically referred to as anti and syn.

Title: Re: what s the difference between trans and anti stereochemistry ?
Post by: FeLiXe on October 19, 2006, 08:08:46 AM

normally anti and syn would describe the conformation as in syn-periplanar, syn-clinical, anti-clinical, anti-periplanar (if those are also the English terms)

I think it's ok to call the product anti. in a ring also trans works. maybe anti makes you think the bond can rotate, i don't know.