15. Halogen compounds
A section of Chemistry, 9701
Listing 10 of 284 questions
Compound Q can be synthesised from chlorobenzene in seven steps, using the route shown in . step 1 step 2 step 3 step 4 step 5 acidified CH3OH step 6 step 7 SOCl2 Cl Cl AlCl3 and CH3Cl CH3 Cl CHO Cl CN chlorobenzene J K L M N OH Cl COOH OH Cl COOCH3 OH P Cl COOCH3 Cl Q Cl COOCH3 N S HN S and K2CO3Write an equation for the formation of the electrophile for step 1. Complete the mechanism in for step 1, the alkylation of chlorobenzene. Include all relevant curly arrows and charges. Draw the structure of the intermediate. Cl Cl intermediate CH3 + Step 2 is an oxidation reaction. Construct an equation for the reaction in step 2. Use to represent an atom of oxygen from an oxidising agent. Suggest reagents for the conversion of K to M in steps 3 and 4. step 3 step 4 Identify the type of reaction that occurs in step 5. Step 7 takes place when P is heated with a weak base such as K2CO3. P Cl COOCH3 Cl Q Cl COOCH3 N S step 7 HN S and K2CO3Suggest why a strong base such as NaOHis not used for this reaction. Q is optically active. Explain the meaning of optically active. Give two reasons why it might be desirable to synthesise a single optical isomer of Q for use as a drug. Q is commonly used in conjunction with aspirin. COOH aspirin O O Aspirin is a weak Brønsted–Lowry acid. The pKa of aspirin is 3.49. 75 mg of aspirin dissolves in water to form 100 cm3 of an aqueous solution. Calculate the pH of this solution. [Mr: aspirin, 180.0] pH = Aspirin undergoes acid hydrolysis in the stomach. Give the structures of the organic products of this acid hydrolysis.
9701_m24_qp_42
THEORY
2024
Paper 4, Variant 2
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Halogenoalkanes have been widely used as aerosol propellants, refrigerants and solvents for many years. Fluoroethane, CH3CH2F, has been used as a refrigerant. It may be made by reacting ethene with hydrogen fluoride. You are to calculate a value for the C–F bond energy in fluoroethane. Use relevant bond energies from the Data Booklet, and the equation below to calculate a value for the bond energy of the C–F bond. CH2 = CH2+ HFCH3CH2FΔH o = – 73 kJ mol–1 C–F bond energy = kJ mol–1 Another halogenoalkane which was used as a refrigerant, and also as an aerosol propellant, is dichlorodifluoromethane, CCl2F2. State two reasons why compounds such as CH3CH2F and CCl2F2 have been used as aerosol propellants and refrigerants. CCl2F2 is one of many chlorofluorocarbon compounds responsible for damage to the ozone layer in the stratosphere. By using relevant data from the Data Booklet, and your answer to suggest why CCl2F2 is responsible for damage to the ozone layer in the stratosphere whereas CH3CH2F is not. Both CH3CH2F and CCl2F2 are greenhouse gases. The ‘enhanced greenhouse effect’ is of great concern to the international community. What is meant by the term enhanced greenhouse effect? Water vapour is the most abundant greenhouse gas. What is the second most abundant greenhouse gas? A greenhouse gas which is present in very small amounts in the atmosphere is sulfur hexafluoride, SF6, which is used in high voltage electrical switchgear. What shape is the SF6 molecule?
9701_s11_qp_22
THEORY
2011
Paper 2, Variant 2
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Questions Discovered
284