ASChemistryAQAExam Questions3. Organic Chemistry3.3 Halogenoalkanes

Halogenoalkanes (AQA AS Chemistry)

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3.3 Halogenoalkanes

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3.3 Halogenoalkanes

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11 mark

Reagent X is used to convert  1-bromopropane into butanenitrile.

q1-3-3-easy-mcq-halogenoalkanes

What is the correct identity of X?

  • Concentrated H2SO4

  • Ethanolic KCN

  • Aqueous KCN

  • Excess NH3

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21 mark

CFCs such as CCl3F and CCl2F2 are more stable than chloroalkanes such as CCl4.

What is the reason for their greater stability?

  • Fluorine has a higher electronegativity than chlorine

  • Fluorine radicals are more stable than chlorine radicals

  • The C–F bond is stronger than the C–Cl bond

  • The C–F bond is more polar than the C–Cl bond

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31 mark

Ultraviolet light initiates the reaction between chlorine and methane.

CH4 + Cl2 → CH3Cl + HCl

What happens to the chlorine molecule in this reaction during the initiation step?

  • Heterolytic fission to give an electrophile

  • Heterolytic fission to give a free radical

  • Homolytic fission to give an electrophile

  • Homolytic fission to give a free radical

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41 mark

Which reaction is an example of nucleophilic substitution?

  • CH3CH2Br → CH2=CH2 + HBr

  • CH2=CH2 + HBr → CH3CH2Br

  • C3H7Br + NH3 → C3H7NH2 + HBr

  • C2H6 + Br2 → C2H5Br + HBr

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51 mark

Methane and chlorine react in the presence of UV light.

Which of the following reactions is not a possible termination step?

  • CH3● + CH3● → CH3CH3

  • CH3● + Cl● → CH3Cl

  • Cl● + Cl● → Cl2

  • Cl2 + CH3● → CH3Cl + Cl●

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61 mark

Three different halogenoalkanes are heated separately with aqueous silver nitrate, each reaction produced a precipitate.

Which halogenoalkane will produce a precipitate the fastest?

  • 1-iodopropane

  • They precipitate at the same rate

  • 1-chloropropane

  • 1-bromopropane

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71 mark

What would be the main product of the reaction between 2-bromobutane and ethanolic potassium hydroxide, KOH, which is heated under reflux?

  • Butane

  • Butan-2-ol

  • But-2-ene

  • Butan-1-ol

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81 mark

Potassium cyanide will react with 1-chloropropane, CH3CH2CH2Cl, and form butanenitrile via a nucleophilic substitution reaction.

Which of the following descriptions of the mechanism steps are correct?

 

First step

Second step

A

Curly arrow from the lone pair on the CN- nucleophile to the δ+ carbon atom 

Curly arrow from the C-Cl bond to the chlorine atom

B

Curly arrow from the δ+ carbon atom  to the CN- nucleophile 

Curly arrow from the C-Cl bond to the carbon atom

C

Curly arrow from the lone pair on the CN- nucleophile to the δ- carbon atom 

Curly arrow from the C-Cl bond to the chlorine atom

D

Curly arrow from the δ- carbon atom  to the CN- nucleophile 

Curly arrow from the C-Cl bond to the carbon atom

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    91 mark

    What is the correct IUPAC name and classification of the following molecule?

    q9-3-3-easy-mcq-halogenoalkanes

     

    IUPAC name

    Classification

    A

    1,bromopentane

    Primary

    B

    2-bromopentane

    Secondary 

    C

    2-bromopentane

    Primary

    D

    4-bromopentane

    Secondary

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      101 mark

      Which of the following statements is not correct about the depletion of the ozone layer?

      • CFCs produce free radicals when they are exposed to UV light in the upper atmosphere

      • 2 moles of ozone break down to form 3 moles of oxygen

      • Fluorine and chlorine free radicals can break down ozone molecules in the upper atmosphere

      • This is an example of a free radical substitution reaction

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      11 mark

      Four drops of 1-chloropentane, 1-bromopentane and 1-iodopentane were put separately into three test-tubes containing 1.0 cm3 of aqueous silver nitrate at 60°C.
      A hydrolysis reaction occurred. 

      R represents the pentane chain C5H11– and X the halogen atom.

      H2O (l) + R–X (l) + Ag+ (aq) → R–OH (aq) + AgX (s) + H+ (aq)

      The rate of formation of cloudiness in the tubes was in the order RI > RBr > RCl

      Why is this?

      • the R–X bond polarity decreases from RCl to RI

      • the electronegativity of the halogens decreases down the group

      • the bond enthalpy of R–X decreases from RCl to RI

      • the ionisation energy of the halogen decreases from Cl to I

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      21 mark

      Which statement best describes the mechanism of the reaction between aqueous sodium hydroxide and 2-bromopropane?

      • Attack by a nucleophile on a carbocation

      • Attack by a nucleophile on a carbon atom with a partial positive charge

      • Homolytic bond fission and attack by a nucleophile on a carbocation

      • Homolytic bond fission and attack by an electrophile on a partial positive charge

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      31 mark

      The presence of a halogen in an organic compound may be detected by warming the organic compound with aqueous sodium hydroxide and silver nitrate.

      Which compound would be the quickest to produce a precipitate?

      q3-3-3-medium-mcq-halogenoalkanes

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        41 mark

        In the hydrolysis of bromoethane by aqueous sodium hydroxide, what is the nature of the attacking species and of the leaving group?

         

        attacking group

        leaving group

        A

        B

        C

        D

        nucleophile

        electrophile

        nucleophile

        electrophile

        nucleophile

        nucleophile

        electrophile

        electrophile

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          51 mark

          Which pair of reactions shows the correct sequence of attack of CFC molecules with ozone?

           

          Reaction 1

          Reaction 2

          A

          F● + O3 → FO● + O2

          FO● + O3 → 2O2 + F●

          B

          Cl + O3 → ClO● + O2

          ClO● + O3 → 2O2 + Cl

          C

          Cl● + O3 → ClO● + O2

          ClO● + O3 → 2O2 + Cl●

          D

          Cl ● + O3 → ClO + O2

          ClO + O3 → 2O2 + Cl●

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            61 mark

            Aqueous sodium hydroxide reacts with 1-chlorobutane to give butan-1-ol.

            How should the second step in the mechanism be described?

            • By a curly arrow from the C-Cl bond to the Cl atom

            • By a curly arrow from the Cδ+ to the C-Cl bond

            • By a curly arrow from the C–Cl bond to the C atom

            • By the homolytic fission of the C–Cl bond

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            71 mark

            What is the correct IUPAC name and classification of the following molecule?

            q7-3-3-medium-mcq-halogenoalkanes

             

            IUPAC name

            Classification

            A

            2,methyl,2,bromobutane

            Tertiary 

            B

            3-methyl-3-bromobutane

            Secondary 

            C

            2-bromo-2-methylbutane

            Secondary

            D

            2-bromo-2-methylbutane

            Tertiary 

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              81 mark

              Which reagents and conditions are required for the following reaction to take place?

              CH3CH2CH2I → CH3CH2CH2CN

              • heated under reflux, aqueous potassium cyanide

              • heated under reflux, ethanol, potassium cyanide

              • ethanol, potassium cyanide

              • warm, aqueous potassium cyanide

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              91 mark

              What would be a possible mix of products for the reaction when 2-iodopentane is warmed with ethanol and concentrated sodium hydroxide under reflux?

              • E-pent-2-ene, Z-pent-2-ene and pentan-1-ol 

              • pent-1-ene, pent-2-ene

              • pent-1-ene, E-pent-2-ene and Z-pent-2-ene

              • pent-1-ene, pentan-2-ol

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              101 mark

               1-chloropropane is reacted with excess ammonia, NH3, in ethanol. Which of the following statements is correct?

              • The addition of excess ammonia favours the production of a tertiary amine, tripropylamine

              • A solid quaternary ammonium salt is formed due to further substitution

              • Excess ammonia favours the formation of a primary amine, propylamine

              • 1-chloropropane is attacked by an NH3 molecule which can act as an electrophile

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              11 mark

              When a solution of potassium cyanide in ethanol is heated under reflux with 2-bromobutane, what is the organic product of the reaction called?

              • 2-methylbutanenitrile 

              • 1-bromobutanenitrile

              • Butanenitrile

              • Pentanenitrile

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              21 mark

              Shown below is a reaction sequence starting with 1-chlorobutane and finishing with butene. 

              q2-3-3-hard-mcq-halogenoalkanes

              What is the correct reaction type and reagent for Step 1 and Step 2?

               


               

              Step 1

              Step 2

              Type of reaction

              Reagent(s)

              Type of reaction

              Reagent(s)

              A

              Nucleophilic substitution

              H2O

              Hydrolysis

              Concentrated H3PO4

              B

              Addition

              KCN in ethanol

              Substitution

              KCl (aq) and concentrated acid

              C

              Nucleophilic substitution

              NaOH (aq) 

              Elimination

              Al2O3

              D

              Substitution

              H2O

              Substitution

              KCN in ethanol

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                31 mark

                A student mixes 2 cm3 of ethanol with 5 cm3 drops of different halogenoalkanes and warms the mixtures in a water bath at 50 °C. They then add silver nitrate solution. Which halogenoalkane will precipitate the fastest?

                • CH3C(CH3)ClCH3

                • CH3CHICH3

                • CH3C(CH3)ICH3

                • CH3CH2CH2I

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                41 mark

                How many different products can be formed if 3-bromo-2-methylpentane undergoes elimination? 

                • 2

                • 3

                • 4

                • 5

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                51 mark

                The depletion of ozone, O3, is caused by the reaction of CFC molecules in the upper atmosphere. Ozone molecules are broken down into oxygen molecules.

                What type of reaction is responsible for the depletion of ozone molecules?

                • Free radical addition

                • Propagation

                • Photolysis

                • Initiation 

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                61 mark

                Which condition would see the production of a solid product from the nucleophilic substitution reaction between 1-iodopropane and ammonia?

                • A large excess of ammonia 

                • Equal concentrations of ammonia and 1-iodopropane

                • Heating under reflux

                • A large excess of 1-iodopropane

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                71 mark

                Which are the correct product(s) for the reaction between 1-chlorobutane and ethanolic potassium hydroxide heated under reflux?

                • But-1-ene 

                • A mixture of but-2-ene and butan-2-ol 

                • Butan-2-ol 

                • A mixture of but-1-ene and butan-1-ol

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                81 mark

                Which of the following mechanisms is not involved in the following reaction sequence?

                Propane → 2-bromopropane → Propan-2-ol → Propene → 2-iodopropane

                • Electrophilic addition

                • Free radical substitution

                • Elimination

                • Nucleophilic addition 

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                91 mark

                Which of the following is not a correct statement about hydrofluorocarbons, HFCs?

                • HFCs do not release free radicals in the stratosphere

                • HFCs are potent greenhouse gases 

                • HFCs contain H-F bonds which have a lower bond enthalpy than H-Cl bonds 

                • HFCs do not contribute to the destruction of the ozone layer

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                101 mark

                Which of the following descriptions of the elimination reaction mechanism is correct when 2-methyl-2-chlorobutane reacts with ethanolic sodium hydroxide?

                q10-3-3-hard-mcq-halogenoalkanes

                 

                First step

                Second step

                Third step

                A

                Curly arrow from lone pair on OH- to H atom in C-H bond adjacent to C-Cl

                Curly arrow from C-H bond to C-C bond

                Curly arrow from C-Cl bond to Cl atom

                B

                Curly arrow from lone pair on OH- to δ+C atom

                Curly arrow from C-C bond to C-H bond

                Curly arrow from Cl atom bond to C-Cl atom

                C

                Curly arrow from lone pair on OH- to H atom in C-H bond adjacent to C-Cl

                Curly arrow from C-C bond to C-H bond

                Curly arrow from Cl atom bond to C-Cl atom

                D

                Curly arrow from lone pair on OH- to δ+C atom

                Curly arrow from C-H bond to C-C bond

                Curly arrow from C-Cl bond to Cl atom

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