Edexcel Jun 2015 Paper 5 Q23

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23 Benzene is sometimes represented as Structure X, shown below, called a Kekul structure after the chemist who suggested it. Structure X (a) What structural feature of benzene shows that Structure X is not an accurate representation? (1)(b) The enthalpy changes for the formation of cyclohexane from cyclohexene and from the actual structure of benzene are given below. 14 + H2 (cid:314) (cid:168)H = 118 kJ mol1 + 3H2 (cid:314) (cid:168)H = 205 kJ mol1 (i) Use the necessary data to estimate the enthalpy change for the theoretical conversion of Structure X to cyclohexane. (1) *P45073RA01428*<br /> (ii) On the enthalpy level diagram below, draw labelled horizontal lines to show the relative enthalpies of the actual structure of benzene, Structure X and cyclohexane. Add an arrow to show the enthalpy change from Structure X to benzene and calculate the value of this enthalpy change in kJ mol1. Write this value next to your arrow. Enthalpy *(iii) Explain the difference in the arrangement of the electrons between benzene and Structure X. (2) (2)*P45073RA01528* 15 Turn over<br /> (c) Benzene reacts with bromine in the presence of a catalyst of iron(III) bromide. Write a mechanism for the reaction of benzene with bromine to form bromobenzene. Include an equation to show the involvement of the catalyst. (4) 16 *P45073RA01628*<br /> (d) (i) State two observations which would be made when phenol reacts with bromine water. (2)(ii) Write the equation for this reaction showing the structure of the organic product. (2) *(iii) Explain why phenol can react with either bromine or with bromine water without a catalyst. (2)(Total for Question 23 = 16 marks) *P45073RA01728* 17 Turn over<br />

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