Addition of `HBr` to but`-1-`ene yields

Options

A. `2-`bromobutane
B. `(+)-2-`bromobutane
C. `(-)-2-`bromobutane
D. `(+-)-2-`bromobutane

Answer

D

Explanation

Addition of `HBt` to but `1-`ene leads to the formation of `2-`bromobutane that contains a stereocenter:
`CH_(3)CH_(2)CH=CH_(2)overset(HBr)rarrCH_(3)CH_(2)overset(**)underset(Br)underset(|)(CH)CH_(3)`
The product exists as a racemic mixture i.e. and equimolar mixture if two enantiomers. The carbocation that is formed in the first step of the addition is trigonal planar and is achiral (it has a plane of symmetry). When the halide ion reacts with this achiral carbocation in the second step, reaction is equally likely at either face. The reactions leading to the two enantiomers occur at the same rate and therefore enantiomers ae produced in equal amounts as a racemic form.