Question

Predict the major product formed by 1,4 -addition of \(\mathrm{HCl}\) to isoprene.

Short answer

Answer: The major product formed by 1,4-addition of HCl to isoprene is CH2─CH(CH3)─C(Cl)(CH3)─CH2.

Step-by-step solution

1. Identify the structure of isoprene

Isoprene is an organic compound with the molecular formula C5H8. Its structure can be represented as: CH2=C(CH3)─CH=CH2

2. Determine the resonance forms of isoprene

In isoprene, electron delocalization occurs due to the presence of conjugated double bonds. The resonance forms can be represented as: Resonance form 1: CH2=C(CH3)─CH=CH2 Resonance form 2: CH2─C+(CH3)─CH=CH2 The second resonance form is more stable as it contains a secondary carbocation with positive charge delocalized onto the more substituted carbon.

3. Identify the nucleophile and electrophile in the reaction

In the reaction, the nucleophile is the chloride ion (Cl-) and the electrophile is the hydrogen ion (H+). HCl will dissociate into H+ and Cl-.

4. Determine the intermediate carbocations formed by electrophilic attack

There are two potential positions for H+ to attack the double bond in isoprene: • If H+ attacks the terminal carbon, a primary carbocation will be formed: CH2─C+(CH3)─CH=CH2 • If H+ attacks the internal carbon with methyl group, a secondary carbocation will be formed: CH2─CH(CH3)─C+(CH3)─CH2 The second carbocation is more stable due to resonance and hyperconjugation. Therefore, the electrophilic attack will occur on the internal carbon.

5. Determine the product formed by nucleophilic attack

The chloride ion (Cl-) will act as a nucleophile and attack the carbocation formed, leading to the formation of the major product. The major product will be: CH2─CH(CH3)─C(Cl)(CH3)─CH2 This is the major product formed by 1,4-addition of HCl to isoprene.