[Bublik]

Hi, 

The question asks if this compound (attached) could have been made from an alkene from a halogenation or halohydrin-forming reaction.

The answer key says yes. I'm having difficulties understanding how - I thought that the Cl's are supposed to be anti- to eachother after a Cl2 addition. I tried to explain this mechanistically, with the chloronium ion and I just don't see anything that would suggest syn- stereochemistry. I'm guessing it has something to do with the tertiary carbon, but I can't figure it out...

[AlphaScent]

the stereochemistry  is controlled, in this case, by the chloronium ion formed.  it  as dds anti. no syn is observed. I would love to be told differently so I can learn, but I am sure the key is wrong. no syn with cl2.

[Babcock_Hall]

Does the process have to be one step?

[orgopete]

Hint, was the alkene cis or trans?

[Bublik]

orgopete, you are brilliant 

This totally blew my mind though. I thought I was fluent in these basic introductory reactions, but I guess not.

The alkene must have been cis. The compound is then part of a racemic mixture.

Here is the link that explained it to me, after I followed through orgopete's hint: http://www.chemgapedia.de/vsengine/vlu/vsc/en/ch/12/oc/vlu_organik/alkene/halogenaddition_an_alkene.vlu/Page/vsc/en/ch/12/oc/alkene/stereochemie/stereochemie_addition.vscml.html

So then, I am forced to conclude that there is a common misconception: anti-addition does not necessarily mean that the products will end up anti to each other.

[clarkstill]

So then, I am forced to conclude that there is a common misconception: anti-addition does not necessarily mean that the products will end up anti to each other.

It just depends what way you draw the molecule! They are always anti with respect to the starting material, but whether you choose to draw the product in one orientation with a wedge or another with a hatch is unimportant...

[AlphaScent]

It is better to know why you got the question wrong than to get the question right..

Cheers, orgopete

As soon as I read that I realized I was looking at the problem from the wrong perspective.

[Bublik]

Ah, I always thought anti meant one had to be a wedge and the other a dash. I'm glad we cleared that up, thanks!

[zsinger]

Any response from Orgopete or Dr.Lennox is pretty much guaranteed to be right.  Listen to these sage voices.
         -Zack