2021_NJC_H3_Chemistry_P1_Question Paper

[Turn over NATIONAL JUNIOR COLLEGE SH2 Preliminary Examination Higher 3 CANDIDATE NAME SUBJECT CLASS REGISTRATION NUMBER CHEMISTRY Paper 1 Candidates answer on the Question Paper Additional Materials: Data Booklet Insert 9813/01 Friday 17 September 2021 2 hours 30 minutes READ THE INSTRUCTIONS FIRST Write your subject class, registration number and name 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 two questions. 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 Section A 1 /13 2 /18 3 /12 4 /17 Section B (circle the attempted questions) 5 /20 6 /20 7 /20 Percentage /100 This document consists of 28 printed pages.

NJC/H3 Chemistry Preliminary Examination/01/2021 2 Section A Answer all the questions in the spaces provided. 1 The information provided in the insert is taken from a number of published scientific articles. Other published articles may not agree with all of this information. You should read the whole insert before you start to answer any questions and use the information it contains to answer the questions. (a) Cyclohexanol 4a is the major stereoisomer formed in the screening experiments. (i) Draw the structure of the organocatalyst most suitable for the synthesizing cyclohexanol 4a. [1] (ii) Based on the mechanism in figure 1, write a balanced equation for the reaction to synthesize cyclohexanol 4a. [1] (iii) Suggest the condition(s) best for the formation of highly substituted optically active cyclohexanol 4a. Explain your answer. [1] (iv) Suggest three advantages of asymmetric domino reactions using organocatalysts in organic synthesis. [3] (v) Draw the 2 conformers of cyclohexanol 4a. Suggest which structure is the major conformer. Explain your answer. [2] (b) The mechanism for the reaction involves 4 steps. (i) Using suitable diagram, suggest how the stereochemistry at carbon d and e in cyclohexanol 4 was introduced. [3] (ii) Draw a suggested mechanism for step 3. [2] [Total: 13]

NJC/H3 Chemistry Preliminary Examination /01/2021 [Turn over 3 2 (a) (i) Using suitable diagram, calculate the bond order of Li2+. [2] (ii) Suggest whether Li2+ exhibits