9701 MCQ Solution 5

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Question 5: [Physical > Bonding]:

Which of the following molecules has no permanent dipole?

A CCl₂F₂

B CHCl₃

C C₂Cl₄

D C₂H₅Cl

Reference: Past Exam Paper – November 2002 Paper 1 Q5

Solution 5:

Answer: C

The compound in A is a halogenoalkene that can exhibit cis-trans isomerism. Due to this it may or may not have a permanent dipole thus option A is eliminated. The compound in B has 1 carbon atom bonded to 3 chlorine atoms and 1 hydrogen atom. The difference in electronegativity between the hydrogen and carbon atom will not match the difference in electronegativity between the opposite chlorine and carbon atom. Due to this mismatch the molecule will overall exhibit a partial charge and thus a permanent dipole, eliminating option B as a correct answer. The compound in C does not exhibit cis-trans isomerism due to the fact that the unsaturated carbon atoms are both bonded to 4 identical chlorine atoms. All differences in electronegativities cancel out thus no overall permanent dipole. This means that C is the correct answer. For arguments sake, the compound in D has 5 hydrogen atoms bonded to a carbon atoms and 1 chlorine atom bonded to a carbon atom, similar to the scenario in compound B, this will cause a permanent dipole thus eliminates D as the correct answer.