RI_H2_Chem_P3 Prelim

RAFFLES INSTITUTION 2014 YEAR 6 PRELIMINARY EXAMINATION Higher 2 CHEMISTRY 9647/03 Paper 3 Free Response 23 September 2014 Candidates answer on separate paper. 2 hours Additional Materials: Writing Paper Data Booklet READ THESE INSTRUCTIONS FIRST DO NOT open this question booklet until you are told to do so. Write your name, class and index number in the spaces provided on the cover page. 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. Begin each question on a fresh sheet of paper. A Data Booklet is provided. Do not write anything on it. 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. At the end of the examination, fasten all your wo rk securely together, with the cover page on top. ______________________________________________________________________________ This document consists of 14 printed pages.

2 Raffles Institution 2014 9647/03/S/14 [Turn Over Answer any four questions. Begin each question on a fresh sheet of paper. 1 (a) Nitrobenzene is formed when benzene is treated with concentrated nitric acid and concentrated sulfuric acid. The reaction proceeds via the formation of an electrophile, a nitronium ion, NO2 +. (i) Draw a dot-and-cross diagram of NO2 +. Nitric acid accepts a proton from sulfuric acid to form H 2NO3 + and HSO 4 –. This is followed by the loss of water from H 2NO3 + to produce the nitronium ion. The mechanism is initiated by the donation of a lone pair of electrons from the oxygen atom of the O─H bond in nitric acid to a hydrogen atom in sulfuric acid. (ii) Use the information given above to draw out the full “curly arrows” mechanism for the formation of the nitronium ion. You are advised to use structural formulae to show clearly the charges on all the species and which bonds are broken and formed. (iii) With the aid of an equation, show how H 2SO4 behaves as a catalyst in the nitration reaction. (iv) Explain why the nitration of phenol  occurs more readily than the nitration of benzene,  gives two products, 2-nitrophenol and 4-nitrophenol. [6] (b) Chlorobenzene can be converted to phenylamine at low temperature using the amide ion (NH 2 –) as a nucleophile. This reaction involves the formation of a very reactive intermediate called benzyne, C 6H4. Benzyne contains a carbon -carbon triple bond. (i) Draw the structural formula of benzyne and explain why