Question

$\text{286. }CH_2=C=CH_2 \xrightarrow{\text{HCl (excess)}}$

• A. 2-chloropropene
• B. 2,2-dichloropropane
• C. 1,2-dichloropropane
• D. 1,1-dichloropropane

Answer 1

Answer: (B)

2,2-dichloropropane

Answer 2

The reaction involves the electrophilic addition of excess HCl to allene ($CH_2=C=CH_2$).

The first addition of HCl to allene yields 2-chloropropene ($CH_3-C(Cl)=CH_2$) via a resonance-stabilized vinylic carbocation intermediate.

The second addition of excess HCl to 2-chloropropene follows Markovnikov's rule. The proton adds to the terminal carbon ($CH_2$) to form a more stable tertiary carbocation ($CH_3-C(Cl)-\overset{+}{C}H_3$). The chloride ion then attacks this carbocation, resulting in the formation of 2,2-dichloropropane ($CH_3-C(Cl)(Cl)-CH_3$).