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JAMB Chemistry 1980 Question 43

Question 43

Introduction to Organic Chemistry

Which of the following is the correct order in increasing boiling point, of the isomeric C5H12 compounds?

Diagram for this question
  1. A.C–C–C–C–C < C–C(C)–C–C < C–C(C)(C)–C
  2. B.C–C–C–C–C < C–C(C)(C)–C < C–C(C)–C–C
  3. C.C–C(C)(C)–C < C–C–C–C–C < C–C(C)–C–C
  4. D.C–C(C)(C)–C < C–C(C)–C–C < C–C–C–C–C
  5. E.C–C(C)–C < C–C(C)(C)–C < C–C–C–C–C
Show the answer and explanation

Answer: D (C–C(C)(C)–C < C–C(C)–C–C < C–C–C–C–C)

Explanation

More branching makes a molecule more compact, with less surface contact and weaker forces between molecules. So 2,2-dimethylpropane (9°C) < 2-methylbutane (28°C) < pentane (36°C).