NYJC 2022 Prelim P3

[Turn over NANYANG JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CLASS TUTOR’S NAME CHEMISTRY 9729/03 Paper 3 Free Response 15 September 2022 2 hours Candidates answer on the Question Paper Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name and class on all the work you hand in. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Answer all questions in the spaces provided on the Question Paper. If additional space is required, you should use the pages at the end of this booklet. The question number must be clearly shown. Section A Answer all questions. Section B Answer one question. Circle the question you attempted in the box below. The use of an approved scientific calculator is expected, where appropriate. A Data Booklet is provided. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use 1 /25 2 /15 3 /20 4 or 5 /20 Total /80 This document consists of 32 printed pages.

2 H2 Chemistry 9729/03 NYJC J2/22 PX [Turn Over Section A Answer all questions in this section. 1 This question is about alkene and diene. Diene is an unsaturated compound containing two double bonds between carbon atoms. (a) Table 1.1 shows the structures of hexa-1,2-diene, hexa-1,3-diene and hexa-1,5-diene. Table 1.1 hexa-1,2-diene hexa-1,3-diene hexa-1,5-diene Table 1.2 shows the enthalpy change of combustion of some organic compounds. Table 1.2 substance Hc / kJ mol−1 Hhydrogenation / kJ mol−1 Liquid hexa-1,2-diene −3867 H1 Liquid hexa-1,3-diene −3816 −225 Liquid hexa-1,5-diene −3843 −252 Liquid hexane −4163 NA Hydrogen gas −286 NA (i) Use data in Table 1.2 to draw an energy level diagram to calculate the enthalpy change of hydrogenation of hexa-1,2-diene, H1. [2] (ii) Suggest which isomer, hexa-1,3-diene or hexa-1,5-diene, is more stable using data in Table 1.2. Explain your answer by considering the type of orbitals present in the carbon atoms of the isomer. [2] (iii) Choose a suitable isomer of hexadiene from Table 1.1 and devise a three -step synthetic route to synthesise buta-1,3-diene. [5] ......................................................................................................................... ......................................................................................................................... ......................................................................................................................... ......................................................................................................................... ......................................................................................................................... ......................................................................................................................... .........................................................................................................................

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4 H2 Chemistry 9729/03 NYJC J2/22 PX [Turn Over (b) When buta-1,3-diene undergoes electrophilic addition reaction with 1 mol of HBr, a mixture of two products, A and B is formed. Both A and B have molecular formula of C4H7Br. + HBr A B A exhibits cis-trans isomerism while B contains a chiral centre. (i) Draw the structures of A and B. [2] (ii) By referring to your structure in (b)(i), explain how cis-trans isomerism arises in A. [2] Kinetic and thermodynamic factors decide the type of addition product that is obtained. A is known as the kinetic product as it is formed faster while B is known as the thermodynamic product as it is formed more slowly and is also more thermodynamically st able than the kinetic product. (iii)