VJC 2025 Tutorial Questions for RX

1 VICTORIA JUNIOR COLLEGE CHEMISTRY DEPARTMENT Halogen Derivatives (Halogenoalkanes and Halogenoarenes) Tutorial Questions Complete the following tables: (1) Preparation of halogen derivatives Preparation of halogenoalkanes Starting compound Reagents and conditions Product HO CH3 Cl CH3 HCl(g) Preparation of halogenoarenes Cl 2, anhydrous AlCl3 Cl (2) Reactions of halogen derivatives (a) Halogenoalkanes Starting compound Reaction type Reagents and conditions Product CH3CHClCH3 NaOH(aq), heat CH3CH(NH2)CH3 Limited NH3 in ethanol, heat in sealed tube

2 Starting compound Reaction type Reagents and conditions Intermediate Reaction type, reagents and conditions Final product CH3CHClCH3 CH3CH(CN)CH3 Hydrolysis H2SO4(aq), heat CH3CHCH3 CH2NH2 Starting compound Reaction type Reagents and conditions Product (CH3)2CClCH2CH3 NaOH in ethanol, heat (b) Halogenoarenes and vinyl halides Compound Reactivity Br No reaction under normal laboratory conditions. CH3CI=CH2

3 Preparation of Halogenoalkanes 1 State the reagents and conditions needed for the conversion of CH3CH2CH2CH2OH into (a) 1–bromobutane …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. (b) 2–bromobutane (in two steps) …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. Reactions of halogenoalkanes 2 2–bromobutane can react under two different sets of reaction conditions to give two different product mixtures C and D. CH3CHBrCH2CH3 I II C4H10O C4H8 C D (a) State the reagents and conditions necessary for each of the reactions I and II. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. (b) Product D is a mixture of isomers, all of which decolo urise bromine water. Draw displayed formulae of these isomers and explain the reaction with Br2(aq). …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. ……………………………………………………………………………………………………..

4 (c) State the reagents and conditions for the conversion of CH3CH(Br)CH2CH3 into CH3CH(NH2)CH2CH3. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. 3 A monocarboxylic acid R occurs in goat’s milk. R has the following composition by mass: C, 62.1%; H, 10.3%; O, 27.6%. Neutralisation of a sample of 0.10 g of R requires 8.6 cm 3 of 0.10 mol dm –3 sodium hydroxide. (a) Determine the molecular formula of R. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. (b) R can be synthesized in the laboratory from 1– bromo–2,2–dimethylpropane by a 2– stage reaction sequence: 1–bromo–2,2–dimethylpropane  Q  R (i) Draw the skeletal formula of 1–bromo–2,2–dimethylpropane. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. (ii) Suggest the reagents and conditions necessary for each step of the synthesis. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ………………………………………………………………………………………………..

5 (iii) Predict from this synthesis the structural formulae of Q and R. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. 4 The alkaloid coniine is the major constituent of oil of hemlock, the poison taken by Socrates when he committed suicide in 399 BCE. H N CH2CH2CH3 coniine Coniine can be synthesized by reacting ammonia with a dibromo compound J. NH3 + C8H16Br2  coniine + 2HBr J (a) What type of reaction is occurring here? …………………………………………………………………………………………………….. (b) Suggest the structure and name of compound J. …………………………………………………………………………………………………….. ………………………………………………………………………………………………… Nucleophilic substitution mechanisms 5 (a) A sample of (2– chloroethyl)benzene, C 6H5CH2CH2Cl, underwent hydrolysis when heated with dilute aqueous NaOH. The kinetics of the study show that the reaction is overall second order. By showing relevant lone pairs and dipoles, and use curly arrows to indicate the movement of electron pairs, describe the mechanism for the hydrolysis of (2–chloromethyl)benzene. (b) (1– chloroethyl)benzene, C 6H5CH(Cl)CH3, is a positional isomer of (2– chloroethyl)benzene. (i) State the type of stereoisomerism exhibited by (1–chloroethyl)benzene and draw its stereoisomers. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ………………………………………………………………………………………………..

6 (ii) When a sample containing purely one of the stereoisomers of (1–chloroethyl)benzene underwent hydrolysis in NaOH(aq ), the product was found to be optically inactive. By showing relevant lone pairs and dipoles, and use curly arrows to indicate the movement of electron pairs, describe the mechanism for the hydrolysis of (1–chloroethyl)benzene. Explain why the product was optically inactive. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. (iii) Suggest reasons for the difference in mechanisms in (a) and (b)(ii). ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. Effect of different halogen atoms on reactivity of halogenoalkanes 6 Why does the reaction C 2H5X + OH– → C2H5OH + X– take place more rapidly in aqueous solution when X is I than when X is Br? A The I– ion is a stronger nucleophile than the Br– ion. B The I– ion is less hydrated in solution than the Br– ion. C The C–Br bond is more polar than the C–I bond. D The C–Br bond is stronger than the C–I bond. ( ) Additional notes: ……………………………………………………………………………………………………... ……………………………………………………………………………………………………..

7 Fluoroalkanes and fluorohalogenoalkanes 7 Which of the following would be suitable for use in a fire extinguisher? 1 CBrF 3 2 CH3(CH2)5CBr3 3 HF A 1, 2 and 3 B 1 and 2 only C 2 and 3 only D 1 only ( ) Additional notes: ……………………………………………………………………………………………………... …………………………………………………………………………………………………….. 8 Ozone depletion potential (ODP) is a measure of the effectiveness of chlorofluoroalkanes in destroying stratospheric ozone. In which sequence are compounds listed in increasing order of their ODPs? A CHClF 2 < CH3CCl2F < CCl2FCClF2 B CHClF2 < CCl2FCClF2 < CH3CCl2F C CCl2FCClF2 < CHClF2 < CH3CCl2F D CH3CCl2F < CCl2FCClF2 < CHClF2 ( ) Additional notes: ……………………………………………………………………………………………………... Halogenoarenes 9 A mixture of 1 mol of bromobenzene and 1 mol of 2– bromopropane is heated under reflux for several hours with 2 mol of sodium hydroxide in aqueous solution. (a) How many moles of bromobenzene and 2–bromopropane are likely to remain? …………………………………………………………………………………………………….. (b) Give 2 reasons to explain the low reactivity of bromobenzene towards nucleophilic substitution. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. ……………