Question

(a) Racemisation occurs in SN1 reactions. Why?(b) Which alkyl halide from the following pairs would you expect to react more rapidly by an SN2 mechanism and why?CH3-CH2-CH2-Br, CH3 CH2-CH-CH3 | Br

Answer 1

a) Racemisation occurs in SN1 reaction because in case of SN1 a group (base/nucleophile) attack from( in front and back side) both side.
b)in case of second one it has two two acidic hydrogen. thus two path way for this one.

Answer 2

Answer:

(a) Due to the production of mixture enantiomer in equal proportions.

(b) $CH3-CH2-CH2-Br$ is primary in nature it will react more rapidly by an SN2 mechanism.

Explanation:

(a) In SN₁ reaction production of mixture enantiomer takes place in equal proportions which will have zero optical rotation, as the rotation due to one isomer is canceled by the rotation due to other isomers. Thus racemization takes place.

(b) The primary alkyl halide gives SN₂ reaction much faster than other alkyl halides. Since $CH3-CH2-CH2-Br$ is primary in nature it will react more rapidly to an SN2 mechanism.