21. Organic synthesis
A section of Chemistry, 9701
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Carvone occurs in spearmint and a stereoisomer of carvone occurs in caraway seeds. Treating either isomer with hydrogen over a nickel catalyst produces a mixture of isomers with the structural formula X. O OH carvone X H2 + Ni State the type of stereoisomerism carvone can show. Explain your answer. Write an equation, using molecular formulae, for this conversion of carvone to X. X can be synthesised from methylbenzene by the following route. X NO2 step 1 methylbenzene step 2 OH NH2 N2 +Cl – step 3 step 5 OH step 6 step 4 Name the mechanism in step1. What type of reaction is occuring in the following steps? step 3 step 5  Suggest reagents and conditions for each of the following steps. step 1 step 2 step 3 step 4 During step 6, hydrogen is added to the benzene ring to produce the cyclohexane ring in X. The six hydrogen atoms are all added to the same side of the benzene ring. State the reagents and conditions needed for this reaction. Complete the part structure to show the structure of the isomer of X that would most likely be obtained during this reaction. X
9701_s17_qp_41
THEORY
2017
Paper 4, Variant 1
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The amino acid tyrosine can be synthesised from phenol by the route shown. step 1 step 2 step 5 step 4 1. PCl 5 2. H2O step 3 HO CO2H NH2 HO CO2H Cl HO CO2H OH HO HO HO CHO CN OH tyrosine phenol Name the mechanism occurring in the following steps. step 1 step 2 What type of reaction is occurring in step 3? Suggest reagents and conditions for each of the following steps. step 1 step 2 step 3 step 5 Draw the structures of the products of the reactions of tyrosine with an excess of each of the following reagents. with NaOHwith HCl with Br2 Question 8 continues on the next page. The dipeptide phe-tyr has the following structure. CO2H H N O OH H2N A mixture of this dipeptide (phe-tyr) and its two constituent amino acids (phe and tyr) was subjected to electrophoresis in a buffer at pH 12. At the end of the experiment the following results were seen. Spots R and S remained very close together. + – mixture applied here P R S The three spots are due to the three species phe, tyr and phe-tyr. Which species is responsible for spot P? Explain your answer. Suggest why the other two species give spots R and S that are so close together.
9701_s17_qp_42
THEORY
2017
Paper 4, Variant 2
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Carvone occurs in spearmint and a stereoisomer of carvone occurs in caraway seeds. Treating either isomer with hydrogen over a nickel catalyst produces a mixture of isomers with the structural formula X. O OH carvone X H2 + Ni State the type of stereoisomerism carvone can show. Explain your answer. Write an equation, using molecular formulae, for this conversion of carvone to X. X can be synthesised from methylbenzene by the following route. X NO2 step 1 methylbenzene step 2 OH NH2 N2 +Cl – step 3 step 5 OH step 6 step 4 Name the mechanism in step1. What type of reaction is occuring in the following steps? step 3 step 5  Suggest reagents and conditions for each of the following steps. step 1 step 2 step 3 step 4 During step 6, hydrogen is added to the benzene ring to produce the cyclohexane ring in X. The six hydrogen atoms are all added to the same side of the benzene ring. State the reagents and conditions needed for this reaction. Complete the part structure to show the structure of the isomer of X that would most likely be obtained during this reaction. X
9701_s17_qp_43
THEORY
2017
Paper 4, Variant 3
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The reagent and conditions required for the nitration of benzene, benzoicacid and phenol are shown in Table6.1. Table 6.1 compound reagents and conditions for nitration benzene concentrated HNO3, 50 °C, concentrated H2SO4 catalyst benzoic acid concentrated HNO3, 100 °C, concentrated H2SO4 catalyst phenol dilute HNO3, 20 °C Concentrated HNO3 reacts with concentrated H2SO4 to generate the electrophile NO2 +. Complete Fig.6.1 to show the mechanism of the reaction between benzene and NO2 +. Include all relevant curly arrows and charges. NO2 +  Write an equation to show how H2SO4 is regenerated. Draw the major products from the mononitration of benzoic acid and of phenol. major product from benzoic acid major product from phenol  Compare the relative ease of nitration of benzene, benzoic acid and phenol. Explain your reasoning; include reference to the structures of the three compounds in your answer. > > easiest least easy  The azo compound Congo Red is used as an acid–base indicator and can be made by the route shown in Fig.6.2. In step 3 of this synthesis, compoundY reacts with compoundZ. CompoundZ is made from compoundX. Assume that the –SO3 – Na+ groups do not react. O2N NH2 N N SO3 – Na+ NO2 step 1 step 2 step 3 Congo Red NaOHX C12H12N2 Z + Y C10H8NO3SNa NH2 SO3 – Na+ N N Suggest structures for compounds X, Y and Z and draw them in the boxes in Fig.6.2. Give the reagents and conditions for step1 and step2. step 1 step 2  
9701_s22_qp_42
THEORY
2022
Paper 4, Variant 2
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