What alkene should be used to synthesize 3-bromohexane? How can I explain the carbocation process?

1 Answer
Jul 28, 2015

You can start with 3-hexene. Since the molecule is symmetrical through its double bond, it doesn't matter whether you add Br to carbon 3 or 4. You will get the same thing. Neither carbon (3 or 4) has more protons than the other.

From here, all you need to know is that since there is only one -Br on the product, it must be a hydrobromination of the appropriate alkene.

It also does not matter whether you use (Z)- or (E)-3-hexene, because the final product has no isomeric specification.

H_3C CH_2(HC=CH)CH_2CH_3 + HBr -> H_3C CH_2(HCBr-CH_2)CH_2CH_3

The carbocation intermediate forms after the nucleophilic alkene donates its pi electrons to grab the proton from HBr (the electrophile), and then Br^- acts as a nucleophile and donates electrons to attach onto the carbocationic center.