Hello guys,
I hope it's legal to ask this question on here now that the quiz is over. I had a question about the first reaction. 2,3-dimethyl, 4-bromohexane was reacted with ethyl oxide. [CH3-CH3(CH3)CH3(CH3)CH3(Br)CH3CH3] + [CH3CH20-]. Sorry, I can't figure out how to do super/subscripts on here. Anyway, problems came for me when I was trying to decide the stereochemistry of the product. The nucleophile is strong, and we were asked to give the major elimination product, so I assume it was an E2 reaction. The H bound to the beta-carbon with the least hydrogens is found on carbon 3. Assuming the Br and this hydrogen are removed (forming a double bond between carbons 3 and 4), I don't believe their is a way to determine the steriochemistry of the product based on the reactant we are given. My product was E, 2,3 dimethyl, 3 hexene because that is the most stable alkene. But, I don't know if this is correct because what prevents it from being the Z isomer of 2,3 dimethyl, 3 hexene? We aren't given the stereochemistry of the reactant alkyl halide. Am I missing something with this problem?
Thank you,
Dominick DeFelice
your assumption about E2 reaction is right. There is nothing that will prevent it from having a Z product and that is the minor product but it is a minor for a reason and that is due to it being less stable because the two major R groups are on the same side and so they will have some Steric hindrance reaction between them and so they'd rather be on opposite side to minimize that reaction. I hope this helps
ReplyDeleteThis is also what I assumed, however since there is one hydrogen on the beta-carbon from which the hydrogen is being removed, one must know the stereochemistry of the reactant to know the stereochemistry of the product. From page 389 of Bruice: "If the Beta-carbon from which a hydrogen is to be removed is bonded to only one hydrogen, there is only one conformer in which the groups to be eliminated are anti. Therefore, only one alkene proeduct can be formed. The particular steroisomer formed depends on the configuration of the reactant." I see no way to tell the stereochemistry of the reactant, so I don't think it was possible to determine the stereochemistry of the major product. The minor products come from removing one of the two hydrogens on the other beta-carbon. Thank you for commenting, I'm still a little uncertain though.
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