CJC_Prelim H2 Chem 2008 P3

CATHOLIC JUNIOR COLLEGE PRELIMINARY EXAM 2008 CHEMISTRY 9746/03 CHEMISTRY 9746/03 Higher 2 Higher 2 Paper 3 Free Response 8 September 2008 Paper 3 Free Response 8 September 2008 2 hours 2 hours Additional Materials: Data Booklet Additional Materials: Data Booklet Answer Paper Answer Paper READ THESE INSTRUCTIONS FIRST READ THESE INSTRUCTIONS FIRST Write in dark blue or black pen. Write in dark blue or black pen. You may use a soft pencil for any diagrams, graphs or rough working. You may use a soft pencil for any diagrams, graphs or rough working. Do not use correction fluid. Do not use correction fluid. Answer any four questions. Answer any four questions. A Data Booklet is provided. A Data Booklet is provided. You are reminded of the need for good English and clear presentation in your answers. 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. 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. The number of marks is given in brackets [ ] at the end of each question or part question. This document consists of 8This document consists of 8 printed pages and 0 blank page.

2 Answer any four questions. 1 Grignard reagents are organo-magnesium hali des, commonly used in synthesis to prepare a variety of organic compounds. The reaction scheme for the synthesis of 3-methylpentan-2-ol, B, using a Grignard reagent is shown below. The Grignard r eagent is prepared from the alkylhalide A and subsequently acts as a nucleophile before forming the product B. CJC 2008 9746/03/prelim/08 (a) (i) Describe the mechani sm for the reaction in step I. (ii) Hence explain why compound A may be found as an equimolar mixture of two isomers. [ 6 ] (b) An alternative method of preparing 3 -methylpentan-2-ol is through the use of 3-methylpentane as a starting material. (i) Suggest an alternative two-step met hod of preparing 3-methylpentan-2-ol from 3-methylpentane, stating clearly the reagents and conditions required for each step. (ii) Suggest a reason why the synth etic method stated in (b)(i) is not preferred to that of using Grignard reagents. [ 3 ] (c) 3-methylpentan-2-ol is easily converted to other useful organic compounds such as 2-methylbutanoic acid, which is widely used in perfumery. Outline how 3-methylpentan-2-ol may be converted to 2-methylbutanoic acid, giving the structure of any intermediate product(s) formed. [3] (d) There are certain practi cal issues with the use of Grignard reagents, notably slow formation of the Grignard reagent and susceptibility to water in air. (i) The slow starting rate may be offset by cutti