Halogenoalkanes (Edexcel AS Chemistry): Exam Questions

This question concerns halogenoalkanes.

1-chloropropane can react to form organic products as shown in the reaction scheme:

 i) State the reagent and conditions used in Reaction 1.

(2)

ii) Identify a suitable reagent for Reaction 2 and include a reason why this is a particularly useful type of reaction in organic chemistry.

(2)

 Reagent ..................................................

 Reason ..................................................

iii) Explain why, in Reaction 3, the reactants are heated in a sealed container.

(2)

iv) Write the structural formula of the product that will be formed if 1-chloropropane is refluxed with aqueous potassium hydroxide solution.

(1)

The bromoalkanes, X, Y and Z, were each added to a mixture of aqueous silver nitrate and ethanol at 50°C. The rate of hydrolysis was compared by measuring the time for a precipitate to appear. 

The relative rates of hydrolysis are in the order (fastest first)

This question is about halogenoalkanes.

2‐chloro‐2‐methylpropane can be hydrolysed by water.

The equation for this reaction is

(CH₃)₃CCl + H₂O → (CH₃)₃COH + H⁺+ Cl⁻

The graph shows how the concentration of 2‐chloro‐2‐methylpropane changes with time during an investigation of this reaction.

Calculate the rate of reaction at 50s. Show your working on the graph. Include units with your final answer.

Rate of reaction at 50s = ............................

What is the classification of the mechanism for the hydrolysis of 2‐chloro‐2‐methylpropane by water?

The letters X, Y and Z refer to three different halogenoalkanes:

1 cm³ of each of these halogenoalkanes was added to separate test tubes containing 5 cm³ of ethanol and 5 cm³ of aqueous silver nitrate solution in a water bath at 50 °C.

i) State the visible change in the reaction of an ethanol/silver nitrate solution with halogenoalkane X.

Include the formula of the compound responsible for this observation.

(2)

ii) The three halogenoalkanes were placed in order of decreasing rate of reaction. 

Which is the correct sequence?

(1)

Under different conditions, 2‐chloro‐2‐methylpropane can react to produce 2‐methylpropene,

i) State the reagent and conditions needed for this reaction.

(2)

ii) Draw the displayed formula for the repeat unit of a polymer that is made by the polymerisation of 2‐methylpropene, .

(2)

iii) Draw a mechanism for the addition of hydrogen bromide, HBr, to 2‐methylpropene to form 2‐bromo‐2‐methylpropane. Include curly arrows, and any relevant dipoles and lone pairs.

(4)

This is a question about the hydrolysis of halogenoalkanes.

Devise an experiment, giving outline details only, that would enable the relative rates of hydrolysis of halogenoalkanes to be compared.

Explain the trend in the rates of hydrolysis of 1-chlorobutane, 1-bromobutane and 1-iodobutane.

The product of the hydrolysis of 2-bromobutane is butan-2-ol. Both molecules are chiral.

State what is meant by the term chiral, using three-dimensional diagrams of the enantiomers of butan-2-ol to illustrate your answer.

Compare and contrast the mechanism of hydrolysis, using aqueous potassium hydroxide, of the primary halogenoalkane, RCH₂X, with that of the tertiary halogenoalkane, R₃CX.

Include diagrams of any intermediate or transition state.

Curly arrows are not required.

Propene reacts with hydrogen bromide (HBr).

What is the type and mechanism for the reaction of hydrogen bromide with propene?

Draw the mechanism for the reaction of propene with hydrogen bromide to form 2-bromopropane. Include curly arrows, and any relevant dipoles and lone pairs.

2-bromopropane reacts with sodium hydroxide. The conditions used determine the type of reaction that occurs.

Which row correctly shows the conditions and organic product for an elimination reaction?

The rate equation for the reaction of 2-bromopropane with aqueous sodium hydroxide is:

rate = k[2-bromopropane][OH^-]

Draw the mechanism for this reaction. Include curly arrows, and any relevant dipoles and lone pairs.

State the role of the hydroxide ion in the reaction in part (d).

Bromobutanes react with hot ethanolic potassium hydroxide solution to produce gaseous butenes.

Procedure

• 0.0080 mol of liquid 1-bromobutane was injected into a round bottom flask containing hot ethanolic potassium hydroxide.

• After the reaction, the syringe was sealed using a clamp.

• The syringe was then removed from the apparatus and allowed to cool to room temperature (298 K).

Result
The final volume of but-1-ene collected was 22.0 cm³.

State the purpose of the condenser.

Describe a chemical test on the gas in the syringe to identify its functional group.

Include the expected result.

Calculate the percentage of 1-bromobutane which was converted to but-1-ene.

[Molar volume of a gas at r.t.p. = 24 000 cm³ mol^–1]

Before cooling, the volume of but-1-ene in the gas syringe was 24.0 cm³.

Calculate the temperature of the gas in the syringe before it cooled.

[Assume no loss from the gas syringe during cooling, and a constant pressure]

i) Another compound formed from 1-bromobutane under these conditions is butan-1-ol.

Identify the type of reaction taking place to form butan-1-ol.

(1)

ii) The functional group in butan-1-ol can be confirmed using a single chemical test.

What is the single chemical test and expected observation?

(1)

iii) Draw the mechanism for the reaction of 1-bromobutane with hydroxide ions to form butan-1-ol.

Include curly arrows, and any appropriate lone pairs and dipoles.

(3)

Alkene molecules are formed by elimination from 2-bromobutane.

How many isomeric alkene products will be formed in this reaction?