11983.05R 12 Hypochlorous acid has the formula HOCl. It adds to alkenes to form chlorohydrins. CH2 CH2 + HOCl → CH2ClCH2OH (a) (i) Calculate the enthalpy change for the reaction between ethene and hypochlorous acid using the following average bond enthalpies. bond enthalpy/ kJ mol−1 C C 612 C C 347 Cl O 272 C Cl 346 C O 358 [3] (ii) Construct a simple labelled enthalpy level diagram for the reaction between ethene and hypochlorous acid. Insert the enthalpy value calculated in part (i) onto the diagram. enthalpy reaction co-ordinate [2] 11983.05R [Turn over (b) Hypochlorous acid adds to alkenes because it has a polar bond, HO Cl. (i) Explain what is meant by the term polar bond. [2] (ii) Draw the polarity of a hypochlorous acid molecule. [1] (iii) Draw the mechanism, using curly arrows, for the reaction of hypochlorous acid with propene to form CH2ClCHOHCH3. [4] (iv) Name the compound CH2ClCHOHCH3. [2] 11983.05R (v) The compound CH2ClCHOHCH3 is the major product. Draw the structure of the minor product and explain why it is the minor product. [2] (vi) If the reaction in part (iii) is carried out in the presence of sodium nitrite, NaNO2, some CH2ClCHNO2CH3 is formed. Suggest how this compound is formed. [1] (c) Chlorohydrins are useful in synthetic chemistry because they are bifunctional. (i) Suggest the meaning of the term bifunctional. [1] 11983.05R [Turn over (ii) Complete the following reaction scheme for CH2ClCHOHCH3 by drawing the organic products. HBr NaOH(aq) CH2ClCHOHCH3 KCN PCl5 [4]