Which of the following represents the equation for the reaction between ethane and chlorine in the presence of UV radiation?
Correct answer: B. C2H6 + Cl2 -> C2H5Cl + HCl
- A. C2H4 + Cl2 -> C2H2Cl2 + H2
- B. C2H6 + Cl2 -> C2H5Cl + HCl
- C. C2H4 + Cl2 -> 2CH3Cl
- D. C2H4 + O2 -> 2CH2Cl + 2HCl
Explanation
Ethane reacts with chlorine by free radical halogenation in the presence of In the presence of sunlight, Cl2 breaks down (homolytically) to form two chlorine radicals. This is the initiation step. I will use the * symbol to indicate a radical, in fact this should be expressed using a superscript dot.Cl2 => The generated chlorine radical can then react with ethane to give an ethane radical (C2H5*) and HCl.C2H6 + Cl* => C2H5* + HClThe ethane radical then reacts with another molecule of chlorine to generate the initial halogenated product and another chlorine radical which can react again. This is the propagation step.C2H5* + Cl2 => C2H5Cl + Cl*The newly generated chlorine radical can now either react with another molecule of ethane (as above) or react with the halogenated product to give further halogenated products:C2H5Cl + Cl* => C2H4Cl2
This question appeared on the HEC Phase II 2017 paper, which you can sit online with every answer explained.
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About Free Radical Substitution
Free radical substitution explains how alkanes react with halogens under ultraviolet light or heat through initiation, propagation and termination steps. The mechanism involves homolytic bond fission and radical intermediates, while product formation depends on the relative stability of radicals and differs from ionic substitution.
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