Question

Identify ‘A’ and ‘B’ in the following reaction and rewrite the complete reaction:

\[\ce{CH3 - CH = CH2 ->[HBr][Peroxide] A ->[alcoholic KCN][KBr] B}\]

Answer 1

Step 1: Reaction of Propene:

• Normally, HBr adds according to Markovnikov's Rule (Br attaches to the more substituted carbon), but peroxides cause the opposite (Anti-Markovnikov Rule).
• So, Br attaches to the first carbon instead of the middle one.
  \[\ce{CH3 - CH = CH2 + HBr ->[Peroxide]CH3 - CH2 - CH2Br}\]

Step 2: Reaction of 1-Bromopropane with Alcoholic KCN:

• Potassium cyanide (KCN) replaces the Br atom with a CN group.
• This is called nucleophilic substitution.
  \[\ce{CH3 - CH2 - CH2Br + KCN -> CH3 - CH2 - CH2CN + KBr}\]

\[\ce{CH3 - CH = CH2 ->[HBr][Peroxide] CH3 - CH2 - CH2Br ->[alc.KCN] CH3 - CH2 - CH2CN}\]

• A = 1-Bromopropane \[\ce{CH3 - CH2 - CH2Br}\]
• B = Butanenitrile (Propyl cyanide) \[\ce{CH3 - CH2 - CH2CN}\]