NYJC H2 Chem 2012 Prelim P3 QP

NANYANG JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 CHEMISTRY 9647/03 Paper 3 Free Response 18 September 2012 2 hours Additional Materials: Answer Paper Data Booklet READ THESE INSTRUCTIONS FIRST Write your name and class on all the work you hand in. Write in dark blue or black pen on both sides of the paper. 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. A Data Booklet is provided. You are reminded of the need for good English and clear presentation in your answers. 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. Section B This document consists of 9 printed pages and 1 blank page. [Turn over

2 H2 Chemistry 9647/03 NYJC J2/12 PX [Turn Over Answer any four questions 1 Aldehydes and ketones react with primary amines in slightly acidic solution to form imines which have the C=N functional group. For example, propanal reacts with methylamine to give N-methyl-1-propanimine. CH3CH2 C H O CH3NH2 H+ N CH3 H CH3CH2 C propanal N-methyl-1-propanimine (a) Aldehydes and ketones also react with 2,4-dinitrophenylhydrazine (2,4-DNPH) to give compounds that are closely related to imines. (i) Write a balanced equation for the reaction between benzaldehyde and 2,4- DNPH. (ii) State what you would observe in the reaction with 2,4-DNPH. What is the type of reaction? [4] (b) The mechanism for the reaction between benzaldehyde and methylamine is shown below. + H2O – C O H + CH3NH2 C O H N H H CH3 + C OH H N H CH3 carbinolamine H+ C OH 2 H N H CH3 + G + step I step II step III step IV −− −− H+ −− −−imine iminium ion G step V

3 H2 Chemistry 9647/03 NYJC J2/12 PX [Turn Over (i) What is the type of reaction in step I? (ii) The positive charge on the iminium ion, G+, does not reside on a carbon atom. Suggest the structure of G+. (iii) Write equations for step I and step IV to show the movement of electrons, using curved arrow notation. Show the lone pairs of electrons, if any, that are involved in each step. (iv) The maximum rate of formation of imines occurs at a pH of about 4.5. Explain why the rate is slow under very acidic conditions and under alkaline conditions. [6] (c) Acrylamide is a carcinogen. It is formed when potato chips are heated to above 120 °C. Its formation has been linked to the presence of glucose (C 6H12O6) and an α -amino acid L found in relatively high amounts in potato. C C H CONH2 H H H C C OH H C OH H C OH H C OH H C OH H H O acrylamide glucose Glucose reacts with L to form an imine M. At high cooking temperatures, M decomposes to produce only three compounds in equimolar amounts: acrylamide, carbon dioxide and compound N (C6H13NO5). (i) Name the functional groups in acrylamide. (ii) Deduce the structure