2022 TJC Prelims H2 Paper 3 Free Response Qns and Ans

9729 / TJC Prelims / 2022 DO NOT WRITE IN THIS MARGIN [Turn over TEMASEK JUNIOR COLLEGE 2022 JC2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME WORKED SOLUTIONS CENTRE NUMBER S INDEX NUMBER Chemistry 9729/03 Paper 3 Free Response Questions 14 September 2022 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Do NOT open this booklet until you are told to do so. Write your name, civics class, centre number and index number 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. Section A Answer all questions. Section B Answer one question. A Data Booklet is provided. The use of an approved scientific calculator is expected, where appropriate. The number of marks is given in brackets [ ] at the end of each question or part question This document consists of 23 printed pages and 1 blank page. For Examiner’s Use Paper 3 Q1 /18 Q2 /20 Q3 /22 Q4 /20 Q5 /20 Total /80

2 DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2022 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN Section A Answer all the questions in this section. 1 (a) Iodolactonisation reaction was first reported by M. J. Bougalt in 1904 and has since become one of the most effective ways to synthesise lactones. An example of the iodolactonisation is the reaction of 4-pentenoic acid as shown in Fig 1.1. Compound X Fig 1.1 Two simplified steps in the iodolactonisation mechanism are given in Fig 1.2. Compound X Fig 1.2 (i) Suggest the role of HCO3- in step 1. [1] It acts as a Bronsted-Lowry base to abstract H+ from the carboxylic acid.[1] (ii) Suggest the mechanism for reaction taking place in Step 2. Show all charges and relevant lone pairs and show the movement of electron pairs by using curly arrows. [3] • Electrophilic addition Name of mechanism [1] Mechanism [2] δ+ δ-

3 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2022 DO NOT WRITE IN THIS MARGIN [Turn over (iii) Sketch a well -labelled reaction pathway diagram for the reaction in Step 2, given that the reaction is exothermic. [2] Diagram & labelling:[1] Ea1, Ea2 & ∆H0: [1] (iv) Suggest the structural formulae of the final organic product formed when CH2=CHCH(CH3)CH2CH2COOH undergoes iodolactonisation in a similar process in Fig 1.1. [1]  (b) Carbon monoxide is one of the most widespread and dangerous industrial hazards. The form