2021 HCI SAJC TJC H3 Chemistry QP

This document consists of 36 printed pages and 1 Insert. TEMASEK JUNIOR COLLEGE JC2 Preliminary Examination Higher 3 CANDIDATE NAME CIVICS GROUP / 2 0 CENTRE NUMBER S INDEX NUMBER CHEMISTRY Paper 1 9813/01 21 September 2021 2 hours 30 minutes Candidates answer on the Question Paper. Additional Materials: Data Booklet Insert READ THESE INSTRUCTIONS FIRST Write your Centre number, index number, name and CT 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 the 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 two questions only. The use of an approved scientific calculator is expected, where appropriate. A Data Booklet is provided. The number of marks is given in brackets [ ] at the end of each question or part question. You are reminded of the need for good English and clear presentation in your answers. [Turn over

2 © HCI / SAJC / TJC 2021 9813/01/JC2 Preliminary Examination [Turn over Section A Answer all questions in this section. 1 The information provided in the insert is taken from two published scientific articles. You should read the whole insert before you start to answer any questions and use the information it contains to answer the questions. (a) Suggest two reasons why current methods of performing allylic oxidation is neither scalable nor sustainable. [2] ………………...………………………………………………………………………………………………... ………………………………………………………………………………………………………………….. ………………………………………………………………………………………………………………….. ………………………………………………………………………………………………………………….. ………………...………………………………………………………………………………………………... ………………………………………………………………………………………………………………….. ………………………………………………………………………………………………………………….. ………………………………………………………………………………………………………………….. (b) Allylic oxidation usually begins with the formation of an allyl radical. Table 1.1 lists the bond dissociation energy (BDE) of allylic C –H bond and 1o C–H bond in propene and propane respectively. Table 1.1 BDE/ kJ mol–1 H–CH2CH=CH2 372 H–CH2CH2CH3 423 Use the concepts of electronic effect and Hammond Postulate to explain why allylic oxidation is more easily achieved than oxidation of the 1o C–H bond of an alkane. [2] ………………...………………………………………………………………………………………………... ………………………………………………………………………………………………………………….. ………………………………………………………………………………………………………………….. ………………………………………………………………………………………………………………….. ………………...………………………………………………………………………………………………... ………………………………………………………………………………………………………………….. ………………………………………………………………………………………………………………….. ………………………………………………………………………………………………………………….. ………………...………………………………………………………………………………………………... DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN

3 © HCI / SAJC / TJC 2021 9813/01/JC2 Preliminary Examination [Turn over (c) Fig. 1.1 illustrates the reactions occurring during the electrosynthesis of enone from an allylic substrate. (i) Write balanced half-equations for the reactions occurring at the anode and cathode. [2] (ii) The allylic substrate does not get oxidised directly at the electrode. Instead, R2N–OH is used as the mediator and tBuOOH is used as the co-oxidant to produce the enone. Suggest what you understand by the italicised terms above. [2] (iii) Construct an equation representing the overall chemical transformation that occurs. [1] …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN

4 © HCI / SAJC / TJC 2021 9813/01/JC2 Preliminary Examination [Turn over (d) Refer to Fig. 1.2 to answer the following questions. (i) Use curly arrows to suggest the mechanism for the reduction of TBS -cresol (D) to form E, given that the reaction begins by a single electron transfer from the cathode to the phenyl ring. [3] (ii) Write a balanced half-equation for the reaction occurring at the Mg anode. [1] (iii) Suggest a difference in the product if an inert electrode such as Pt is used in place of Mg. [1] ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN

5 © HCI / SAJC / TJC 2021 9813/01/JC2 Preliminary Examination [Turn over (e) The reduction of D to E shown in Fig. 1.2 was hypothesised to proceed via one of two pathways, A or B:  Pathway A: Li atoms, generated in-situ by the cathode, transfer electrons to D.  Pathway B: D adsorbed onto the electrode before the electrode transfers electrons to D. The energy profile diagrams for both pathways A and B are given below. The number in parenthesis is the free energy of the intermediate species or transition state (TS) relative to L. TS for steps which are barrierless are not shown for clarity. Pathway A Pathway B (ET – electron transfer; PT – proton transfer; ads – adsorption) The rate determining step is the step with the largest activation energy. By identifying the rate determining step for each pathway and calculat ing its activation energy , suggest which pathwa y the reduction of D to E undergoes. [2