Arrange the following alkyl halides in decreasing order of the rate or `beta`-elimination reaction alcoholic KOH.
A. `CH_(3)-underset(CH_(3))underset(|)overset(H)overset(|)(C)-CH_(2)Br`
B. `CH_(3)-CH_(2)-Br`
C. `CH_(3)-CH_(2)-CH_(2)-Br`

Options

A. `A gt B gt C`
B. `C gt B gt A`
C. `B gt Cgt A`
D. `A gt C gt B`

Answer

D

Explanation

Alkyl halides on heating with alcoholic potash eliminates one molecule of halogen acid to form alkene. Hydrogen is eliminated from `beta` - carbon atom. Nature of alkyl group determiners rate of reaction
i.e , `3^@ gt 2^@ gt 1^@ or A gt underset(2^@ beta-"carbon")(C gt B)`
`overset(3^@ beta - "carbon")underset((A))underset(CH_3)underset(|)(CH)-CH_(2)Br" "overset(1^@ beta - "carbon")underset((B))(CH_3-CH_2-Br)`
`underset((C))(CH_3-CH_2-CH_2-Br)`