9701 MCQ Solution 67

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Question 67: [Organic > Halogen Derivatives]

Chlorofluoroalkanes, commonly known as CFCs, undergo homolytic fission by ultraviolet irradiation in the stratosphere.

Which radical could result from the irradiation of CHFClCF₂Cl?

A CHFClĊFCl

B ĊHClCF₂Cl

C ĊHFCF₂Cl

D ĊFClCF₂Cl

Reference: Past Exam Paper –June 2003 Paper 1 Q27

Solution 67:

Answer: C.

In the given CFC above, there are C-H bonds, C-F bonds, C-Cl bonds and a C-C bond. In all the options the C-C bond remains intact. The order of bond strength of the remaining 3 bonds is: C-H>C-F>C-Cl. Thus a C-Cl bond will be broken since it requires the least energy. This only occurs in option C. In option A, the CFC loses a F atom, suggesting that a C-F bond is broken. In option B, The CFC loses a different F atom, yet still suggesting that a C-F bond is broken. In option D, the CFC loses a H atom, suggesting that a C-H bond is broken. According to the order of bond strengths these options are incorrect. Thus option C is the correct answer.