elimination reaction

[donaldduck]

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To support the theory that an E2 rxn is taking place, it would be best useful to use chiral centers on which carbons of a deuterated 2-bromobutane?

A. Carbon 2 only
B. Carbon 3 only
C. both Carbon 2 and Carbon 3
D. Carbons 1,2,3

the correct answer is C. I picked D. I understand why carbons 2.3 are necessary, but my reasoning for picking carbon one is that i thought some of the product that will be formed will have the double bond on carbon 1, even though this is the minor product. Where did i go wrong?

 

[orgohacks]

To support the theory that an E2 rxn is taking place, it would be best useful to use chiral centers on which carbons of a deuterated 2-bromobutane?

A. Carbon 2 only
B. Carbon 3 only
C. both Carbon 2 and Carbon 3
D. Carbons 1,2,3

the correct answer is C. I picked D. I understand why carbons 2.3 are necessary, but my reasoning for picking carbon one is that i thought some of the product that will be formed will have the double bond on carbon 1, even though this is the minor product. Where did i go wrong?

You can't make a chiral center on carbon #1 of 2-bromobutane through deuteration. So even if the elimination happens on C-1, you won't be able to tell E/Z through a deuteration experiment, which means you can't unequivocally determine E2.

[The E2 is stereospecific. You need an anti orientation of proton and leaving group. Chiral centers will become a double bond with a specific E or Z configuration, depending on the orientation of the chiral centers. ]

hope this helps - James