molecular formula of X is C 6 H 4 C l 2 1 c ½ for each structure ½ for each

# Molecular formula of x is c 6 h 4 c l 2 1 c ½ for

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molecular formula of X is C 6 H 4 C l 2 .  (c) [½] for each structure, [½] for each name. Comments: Some students would have struggled with the naming of the compounds using the IUPAC convention. A common mistake was to draw the same structure with a different orientation to pass it off as a different compound. (d)  for Y and  for equation. Comments: For mononitration of compound Y to give only one compound, it must possess a high degree of symmetry and only one possible chemical environment for the substitution of the nitro group. Common mistake: Answer produced a detailed description of the mechanism instead of an equation which showed the reaction with the reagent given. H2 Chemistry 9647 2015 H2 Chemistry 9647 2015 PAPER 3 1 (a) (i) ROH + Na RONa + ½H 2 2ROH H 2 Amount of menthol = 2 x 1.32 x 10 2 = 2.64 x 10 2 mol Mass of menthol = 2.64 x 10 2 x 156 = 4.118 g % by mass of menthol in peppermint = 10 4.12 x 100 % = 41.2 % Note: Students need to recognise mole ratio = 1 menthol : ½ H2 and not 1:1. (ii) Chiral centres: 3 Number of optical isomers = 2 3 = 8 NEW SYLLABUS: enantiomers instead of optical isomers Note: General formula for number of stereoisomers = 2 n where n is the number of chiral centre or double bonds with different R groups. Common mistakes are to create six isomers (3 x 2) or nine isomers (3 2 ) (b) (i) (ii) Energy / kJ mol 1 Reaction pathway Menthone + Hydrogen Menthol H = −80 kJ mol 1 E a = +42 kJ mol 1 Nickel catalysed Platinum catalysed 