15. Halogen compounds
A section of Chemistry, 9701
Listing 10 of 284 questions
Halogenoalkanes react with a number of different reagents in nucleophilic substitution reactions. A sample of potassiumcyanide dissolved in ethanol is added to a sample of 1-bromobutane, CH3(CH2)3Br, and heated under reflux. A nucleophilic substitution reaction occurs and compoundA is formed. Name compoundA. What is meant by the term nucleophile? Identify the nucleophile in this reaction. Explain why this reaction is described as a substitution reaction. State the reagentand conditions needed for CH3(CH2)3Br to react to form CH3(CH2)3NH2. reagentconditions  Equal amounts of three different halogenoalkanes are added to three separate test‑tubes. An equal amount of aqueous silvernitrate and ethanol is added to each test‑tube. The time taken for a precipitate to form is recorded for each halogenoalkane. halogenoalkane time taken for precipitate to form / s (CH3)3CCl (CH3)3CBr (CH3)3CI Describe and explain the trend in reactivity of the different halogenoalkanes shown in this experiment. All three halogenoalkanes tend to react via the SN1 mechanism. Explain why the SN1 mechanism is favoured. Identify a halogenoalkane which tends to react with an aqueous solution of silver nitrate and ethanol via the SN2 mechanism. 
9701_s19_qp_23
THEORY
2019
Paper 2, Variant 3
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An unlabelled bottle contains a straight-chain halogenoalkane, Q. The molecular formula of Q is C5H11X, where X is a halogen; bromine, chlorine or iodine. A test is carried out to identify the halogen present in Q. A sample of Q is added to NaOHand warmed. Dilute nitricacid is then added followed by a few drops of aqueous silvernitrate. A cream precipitate is observed. Suggest the identity of X. Write an ionic equation to describe the formation of the cream precipitate. Include state symbols. Describe a further test which would confirm the identity of X. test expected result  The reaction of Q with NaOHtends to proceed via an SN2 mechanism. Suggest the structural formula of the straight-chain halogenoalkane Q.  Explain why the reaction tends to proceed via an SN2 mechanism rather than an SN1 mechanism. Two different halogenoalkanes, P and R, both with the molecular formula C4H9Cl, are separately dissolved in ethanol and heated under reflux with sodium hydroxide. The major organic product of each of these reactions is methylpropene. Name the type of reaction occurring. Write an equation, using molecular formulae, to represent the reaction occurring. Draw the skeletal formula of methylpropene.  Give the names of P and R. 
9701_s20_qp_22
THEORY
2020
Paper 2, Variant 2
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1,3-dichloropropan-2-ol can be made by reacting M. Cl Cl O M Cl Cl HO 1,3-dichloropropan-2-ol Give the systematic name of M. Name the functional group present in M that changes during this reaction. State a suitable reagent for this reaction. Separate samples of 1,3-dichloropropan-2-ol and 3-chloropropane-1,2-diol are heated with excess acidified Cr2O7 2– until there is no further reaction. In each reaction, a different organic product, Q or R, is made. Cl Cl HO 1,3-dichloropropan-2-ol Q Cl OH HO 3-chloropropane-1,2-diol R Q and R are tested separately with 2,4-dinitrophenylhydrazine solution, 2,4-DNPH, and sodiumcarbonate solution, Na2CO3. Complete the table to give any relevant observations. If no reaction occurs, write ‘no visible change’. reagent observation with Q observation with R 2,4-DNPH Na2CO3 Citric acid can be made from M in a four-step reaction. Cl Cl O step 1 M citric acid step 2 Cl Cl N HO step 3 Cl Cl O HO OH OH HO OH O O O OH step 4 O N N HO OH Complete the table for each step of the reaction sequence to identify: ● the reagents and conditions required ● the type of reaction. step reagent and conditions type of reaction dilute sulfuric acid dilute sulfuric acid  
9701_s21_qp_23
THEORY
2021
Paper 2, Variant 3
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