Question

Assertion (A): Among isomeric pentanes, 2,2-
dimethylpentane has highest boiling point.

Reason (R): Branching dose not affect the boiling point.

• A. Both A and R are not correct.
• B. Both A and R are correct and R is the correct explanation of A.
• C. A is not correct but R is correct.
• D. Both A and R are correct but R is not the correct explanation of A.

Answer 1

The correct option is A Both A and R are not correct.

Solution :

Isomers of Pentane-


Factors affecting Boiling Point-

* Long - chain hydrocarbons have a higher boiling point than branched-chain due to increasing vander Waals forces between molecules . As the length of the chain increases, so dose its surface area, and so the van der Waals forces are stronger.

If branching increases, it decreases the boiling point. Branched-chain alkanes have lower boiling points because the chains cannot pack as closely together. There are fewer points of contact between molecules so the van der Waals forces are weaker.

Hence, both assertion and Reason are wrong statements. Option (C) is correct answer.