SAJC H2 Chem 2013 Prelim P3 QP

1 ST ANDREW’S JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATIONS Chemistry Higher 2 9647/03 Paper 3 16th September 2013 2 hours Candidates answer on separate paper. Additional Materials: Writing paper, Data Booklet, Graph paper READ THESE INSTRUCTIONS FIRST: Write your name and civics group on all the work you hand in. Write in dark blue or black pen. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer any four questions. You are reminded of the need for good English and clear presentation in your answers. The number of marks is given in brackets [ ] at the end of each question or part question. This document consists of 14 printed pages including this page. 1180

2 Answer 4 out of 5 questions. 1 Fructose or fruit sugar (C 6H12O6) is a simple monosaccharide, which is derived from sugar cane, sugar beets and corn. It is a common source of sweetness used in the candy industry. One isomer of fructose is shown below.   D-fructose (a) State the number of chiral centers present in D-fructose. [1] (b) Carbonyl compounds can undergo rapid and reversible reaction with alcohols to form hemiacetals: hemiacetal (i) State the type of reaction for the formation of hemiacetal. (ii) Outline the mechanism of the above reaction using propanone and phenol dissolved in aqueous sodium hydroxide. 1181

3 1 (b) (iii) D-fructose can form two cyclic hemiacetal structures via the mechanism in b(ii). One of the two isomers is α-D-fructopyranose.   An alternative cyclic hemiacetal structure is a five-membered ring, α-D-fructofuranose. Draw the structure of α-D-fructofuranose.   [5] (c) In solution, D-fructose exists as an equilibrium mixture of 70% α-D-fructopyranose and 22% α-D-fructofuranose. (i) Calculate the equilibrium constant, Kc. (ii) Suggest a method to change the numerical value of Kc. [3] (d) α-D-fructopyranose is very soluble in water and insoluble in organic solvents. Hence, they are very difficult to purify. The formation of ether allows the purification to be easier. Silver oxide with iodo-alkane works with alcohol in the formation of ether as shown below:   Rate = k [CH3I][R’OH] (i) State the type of reaction involved in the formation of ether. (ii) Draw the product formed when α -D-fructopyranose reacts with Ag 2O and CH3CH2CH2I. [Turn over] 1182

4 1 (d) (iii) Predict, with reasoning how the rate of d(ii) would differ if (I) CH3 C CH3 CH2I CH3 is used. (II) CH3CH2CH2Cl is used [6] (e) Sucrose undergoes the following reaction at room temperature. This reaction can be catalysed by insects such as honey bees which have protein-like enzymes called invertases. (i) State the type of reaction sucrose under