Optically active destroyer ochem #86

[monsieurwise]

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Hi everyone!
I feel so stupid asking this, but I have a Methylenecyclohexane reacting with Br2/CH2Br2. Why is the product optically unactive? The product have one stereocenter where the Br is attached, why not optically active?
This is destroyer Ochem #86 btw...it's choice a.
Thank you so much guys!!!

 

[athomas]

Hi everyone!
I feel so stupid asking this, but I have a Methylenecyclohexane reacting with Br2/CH2Br2. Why is the product optically unactive? The product have one stereocenter where the Br is attached, why not optically active?
This is destroyer Ochem #86 btw...it's choice a.
Thank you so much guys!!!

It's not optically active because that is NOT a stereocenter. If you look, the ring is the same both ways around, meaning that the carbon you think is chiral actually has 2 identical groups (the ring is the same both ways), and is thus not chiral.

If it was methylene with another substituent ortho or meta to it, then the ring wouldn't be the same each way around and you would have a stereocenter.

Hopefully that helps, it's hard to explain without the figure.

 

[monsieurwise]

Thank you!! I see it now, if I think about it in 3d it's clear why. Thank you =)

 

[patricklin27]

for the answer to this question, it mentions that D only has one enantiomer. Doesnt this molecule have two chiral centers and thus can have a diastereomer? I dont understand why D only has one chiral center.

 

[monsieurwise]

It's true that D have 2 stereocenters. However, this PARTICULAR REACTION add Br2 as anti ONLY. Thus u can't have Br on the same side (so no diasteoreomer).