Question

10 points Save Answer QUESTION 2 Select the expected major product(s) of the following reaction (Hint: Carbocation rearrangement is involved!) HBr + enantiomer + enantiomer

Answer 1

Ans) A & E

A - 2 - bromo 2,3- dimethylbutane

E - 1 - bromo 3,3 - dimethylbutane

The reactant in this reaction is 3,3 - dimethylbut-1-ene. When 3,3 - dimethylbut-1-ene reacts with HBr to give the major product as 2 - bromo-2,3-dimethylbutane.

According to Markovnikov's rule, the acid hydrogen gets adhered with the carbon atom which has more hydrogen substituents, whereas the halide group gets added with the carbon atom which has more alkyl substituents.

By following the Markonikov's rule, when reaction between HBr and the double bond of 3,3-dimethylbut-1-ene as follows.

HBY 2- Bromo -2,3- dimethylbutane 3,3-dimethylbut- l-ene

When 3,3,- dimethylbut-1-ene reacts with Hbr and peroxide 1-bromo-3,3-dimethylbutane is formed. Sn1 mechanism is followed in this reaction, by which primary carbocation is less stable than the intermediate secondary carbocation. The mechanism is

сна H-BY C-CH - CH3 + Br сH3 нс – С – сH = CH) 2 - СН3 3,3-dimethylbut-i-ene СН3 More stable Secondary Carbocation сH3 CH3 Br Bro 1-с-с -с- - с - Hс-с - сн - с - 3 сня сиз Carbocation a-bromo- 3,3-dimethyl butane.

1,bromo-3,3-dimethylbutane is formed when 3,3-dimethylbut-1-ene reacts with HBr in the presence of peroxide. This reaction takes place followed by anti-markovnikov's rule, that is the positive H of HBr will make a bond with carbon with less substituents than carbon with more substituents.

СН3 Peroxide 973 Br — Сн,- C-CH2-CH2 CH - C-CH=CH2 + HBY снэ 1- bromo-3,3- dimethyl burane 3,3-dimethyl but-i-ene