Edexcel Jun 2015 Paper 1 Q18

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18 Alkenes and cycloalkanes have the same general formula, but react very differently with halogens. (a) Give the general formula that applies to both alkenes and cycloalkanes. (b) Using structural formulae, complete the overall equation for the reaction of an alkene of your own choice, containing fewer than four carbon atoms, with liquid bromine. Name the product. + Br2(1) (3) Name:14 *P44879A01424*<br /> *(c) An example of an alkene with six carbon atoms is 2-methylpent-1-ene. It reacts with chlorine by means of an electrophilic addition reaction. The diagram below shows a students attempt at drawing the mechanism for this reaction. (i) Identify the three errors in this students drawing of the mechanism. (3) Error 1Error 2Error 3(ii) The structure of the carbocation intermediate is correctly drawn. Explain why the positive charge is on the carbon atom shown. (1)*P44879A01524* 15 Turn over<br /> (d) There are five possible cycloalkanes, each containing five carbon atoms. Three of the isomers are given below. Complete the other two boxes, by adding the skeletal formulae of the other two structural isomers. (e) Define the term structural isomerism. (2) (1)(f) Another example of a cycloalkane is cyclobutane. This compound, like other cycloalkanes, can also react with chlorine. The overall reaction of cyclobutane with chlorine is as follows: C4H8 + Cl2C4H7Cl + HCl (i) This reaction can occur at room temperature and pressure. What further condition is needed for this reaction to take place? (1)(ii) Using the appropriate arrows, complete the equation for the initiation step of the reaction mechanism for the reaction of chlorine with cyclobutane. (2) Cl Cl16 *P44879A01624*<br /> (iii) Using molecular formulae, write equations for the this mechanism. two propagation steps of First propagation step: Second propagation step: (iv) Name the type of bond fission which occurs in these propagation steps. (2) (1)(v) There are also termination steps in this mechanism. Explain how these differ from the other steps in the mechanism and why these result in the reaction ending. (2)(g) If the reaction with cyclobutane is carried out with an excess of chlorine, how are the products of the reaction affected? (1)(Total for Question 18 = 20 marks) *P44879A01724* 17 Turn over<br />

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