Question

Predict the major product formed when an alkene reacts with a hydrogen halide (e.g., HCl or HBr).

• A. Alkane
• B. Alkyl halide
• C. Alcohol
• D. Ether

Hint:

Addition of hydrogen halides to alkenes usually follows Markovnikov’s rule unless peroxides are present (which causes anti-Markovnikov addition in the case of HBr).

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question asks for the general class of compound that is formed as the major product when an alkene reacts with a hydrogen halide (HX, where X = Cl, Br, I).
Step 2: Key Formula or Approach:
This reaction is a classic example of an electrophilic addition reaction. The electron-rich pi (\(\pi\)) bond of the alkene acts as a nucleophile and attacks the electrophilic hydrogen atom of the hydrogen halide. This breaks the double bond and adds the hydrogen and the halogen atoms across the two carbons. For unsymmetrical alkenes, the reaction follows Markovnikov's rule.
Step 3: Detailed Explanation:
Let's consider a general alkene, \( R-CH=CH_2 \), reacting with HX.
1. The \( \pi \) bond attacks the H of HX, and the H-X bond breaks. The hydrogen adds to one of the carbons of the double bond. Following Markovnikov's rule, the H adds to the carbon that already has more hydrogens (the \(CH_2\) carbon in this case). This forms a carbocation on the more substituted carbon.
\[ R-CH=CH_2 + H^+ \rightarrow R-\stackrel{+}{C}H-CH_3 \] 2. The halide ion (\(X^-\)), which is a nucleophile, then attacks the positively charged carbon (carbocation).
\[ R-\stackrel{+}{C}H-CH_3 + X^- \rightarrow R-CH(X)-CH_3 \] The final product contains a halogen atom bonded to a carbon skeleton, which is the definition of an alkyl halide (or haloalkane).
Step 4: Final Answer:
The major product of the addition of a hydrogen halide to an alkene is an alkyl halide.