2023 EJC H2 Chemistry Prelims Paper 3 (Solutions with comments)

© EJC [Turn Over EUNOIA JUNIOR COLLEGE JC2 Preliminary Examination 2023 General Certificate of Education Advanced Level Higher 2 Paper 3 Suggested Solutions with Marker’s comments Section A 1 (a) Solvolysis is a reaction in which the solvent is one of the reagents and is also present in great excess of that required for the reaction. Usually, the electron -rich solvent molecule substitutes an atom or group in the reactant molecule. One example of solvolysis is the reaction of compound A, C6H5CH2Br, with ethanoic acid as the solvent. This reaction happens via an SN1 mechanism. (i) Describe the mechanism for the reaction between compound A with ethanoic acid. Show relevant lone pairs of electrons, dipoles and curly arrows. [4] (ii) Explain why this reaction mainly proceeds via the SN1 mechanism. [1] (iii) Given that the enthalpy change of the reaction is endothermic, draw a labelled reaction pathway diagram for the reaction involving compound A and ethanoic acid. [2] Another reaction was carried out using C6H5CHBrCH3 with ethanol as the solvent, in the presence of trace amount of sodium hydroxide. This reaction undergoes the same mechanism as the reaction between compound A and ethanoic acid. (iv) Predict the major organic product formed from the reaction of optically pure C6H5CHBrCH3 with ethanol, and comment on the optical activity of the product formed. Briefly explain your answer. [3] (v) By-products are formed during the preparation of many organic compounds. This usually occurs because the reagents can react in more than one way. Suggest a possible by-product, in full structural formula, that can be formed from the above reaction. [1]

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