Question

Unsaturated hydrocarbons generally undergo _____ reactions.

• A. Substitution
• B. Addition
• C. Elimination
• D. Rearrangement

Hint:

Unsaturated hydrocarbons contain multiple bonds and therefore mainly undergo addition reactions.

Answer 1

The Correct Option is B

Concept:
Unsaturated hydrocarbons contain:
• Double bonds \((C=C)\), or
• Triple bonds \((C \equiv C)\) These multiple bonds are reactive and can break easily to add atoms or groups across the bond. Therefore, unsaturated hydrocarbons generally undergo addition reactions.

Step 1: Understanding addition reactions.
In an addition reaction:
• Atoms are added across a double or triple bond.
• The unsaturated compound becomes saturated. Example: \[ CH_2 = CH_2 + H_2 \rightarrow CH_3 - CH_3 \] Here hydrogen gets added across the double bond.

Step 2: Why unsaturated compounds prefer addition reactions.
The \(\pi\)-bond in multiple bonds is weaker than sigma bond and can break easily. Thus, atoms can add across the bond very easily. Hence, unsaturated hydrocarbons mainly undergo: \[ \boxed{\text{Addition reactions}} \]

Step 3: Checking other options.

• Saturated hydrocarbons usually show substitution reactions.
• Elimination reactions remove atoms or groups.
• Rearrangement reactions involve structural changes. Therefore, the correct answer is: \[ \boxed{(2)\ \text{Addition}} \]