Nucleophilic substitution

This question is about rates of reaction.

The rate of hydrolysis of a bromoalkane (RBr) is investigated using this method.

• A boiling tube has a cross drawn onto it.

• An aqueous solution of silver nitrate is added to an ethanolic solution of RBr in the boiling tube in a warm water bath.

• The time is recorded for the cross on the boiling tube to become invisible.

The method is repeated at different temperatures.

State why the cross on the boiling tube becomes invisible.

The volume and concentration of each substance used at each temperature is kept constant.

Identify one other variable that should be kept constant to ensure that the investigation is fair.

The reaction between the bromoalkane RBr and an aqueous solution of KOH is investigated.

The rate constant k for this reaction is determined at a series of temperatures T.

The Arrhenius equation can be written in this form.

Table 2 shows an incomplete set of results for this investigation.

Complete Table 2.

The results in Table 2 can be used to plot a graph to determine the activation energy E_a for this reaction.

Complete the x-axis in Figure 10 by adding an appropriate scale.

Plot the graph on the grid in Figure 10.

Use your graph to determine a value, in kJ mol^–1, for the activation energy E_a

The gas constant, R = 8.31 J K^–1 mol^–1

The rate equation for the reaction between a different bromoalkane (R₂CHBr) and an aqueous solution of KOH is

Which of these is a correct mechanism for the reaction between R₂CHBr and KOH?

Tick (✓) one box.

Explain, in terms of bond polarity, why R₂CHBr and KOH react together.

This question is about an organic synthesis.

Name the mechanism in Step 1.

State the reagent(s) used for Step 1.

Name of mechanism

State the reagent(s) used for Step 4.

Outline the mechanism for Step 4.

Mechanism

This question is about amines.

CH₃CHBrCH₂CH₃ reacts with NH₃

Draw the skeletal formula of the major organic product formed when

• an excess of NH₃ is used

• an excess of CH₃CHBrCH₂CH₃ is used.

Product with excess NH₃

Product with excess CH₃CHBrCH₂CH₃

Figure 3 shows a two-step synthesis to make amine G.

Complete Figure 3 by drawing the mechanism for Step 1 and the displayed formula of amine G.

Figure 4 shows two amines, P and Q.

Explain why P is a stronger base than Q.

Acrylonitrile, H₂C=CHCN, can be used as a starting material for the synthesis of butane-1,4-diamine, as shown in this reaction scheme.

Use IUPAC rules to name isomer W.

Reaction 1 produces a mixture of W and two other isomers.

Draw the structures of the two other isomers.

Explain, by considering the mechanism of this reaction, why all three isomers are formed.

The reaction scheme is repeated here.

Identify the reagent that is warmed with isomer W in reaction 2.

State the other reaction condition needed.

State the reagent and reaction conditions needed for reaction 3.

Give an equation for reaction 3.

Reagent and conditions

Equation

An incomplete equation for the formation of nylon 4,6 from five molecules of butane-1,4-diamine and five molecules of hexanedioic acid is shown.

Deduce the values of x and y in this equation.

Figure 6 shows a section of the nylon 4,6 polymer molecule.

Figure 6

Draw, on Figure 6, another section of nylon 4,6 polymer showing two hydrogen bonds between the two sections.

Under suitable conditions, 2-bromobutane reacts with sodium hydroxide to produce a mixture of five products, A, B, C, D and E.

Products A, B and C are alkenes.

A is a structural isomer of B and C.

A does not exhibit stereoisomerism.

B and C are a pair of stereoisomers.

Products D and E are alcohols.

D and E are a pair of enantiomers.

Give the names of the two concurrent mechanisms responsible for the formation of the alkenes and the alcohols.

Mechanism to form alkenes

Mechanism to form alcohols

Define the term stereoisomers.

Deduce the name of isomer A.

Explain why A does not exhibit stereoisomerism.

Outline the mechanism for the reaction of 2-bromobutane with sodium hydroxide to form alkene A.

Deduce the name of isomer B and the name of isomer C.

Explain the origin of the stereoisomerism in B and C.

Draw 3D representations of enantiomers D and E to show how their structures are related.

A student compares the rates of hydrolysis of 1-chlorobutane, 1-bromobutane and 1-iodobutane.

The suggested method is:

• add equal volumes of the three halogenoalkanes to separate test tubes

• add equal volumes of aqueous silver nitrate to each test tube

• record the time taken for a precipitate to appear in each test tube.

State and explain the order in which precipitates appear.

Order in which precipitates appear

Which compound is formed from bromoethane in a nucleophilic substitution reaction?

Which pair of reagents does not produce ethanol?

This question is about making a diester from cyclohexanol.

State the type of reaction in step 1.

Give the name of the reagent needed for step 1.

State the reagents needed and give equations for step 2 and step 3.

Show the structure of Compound G in your equations.

Step 2 equation

Step 3 equation

Cyclohexane-1,2-diol reacts with ethanedioyl dichloride.

Give the name of the mechanism for this reaction.

Complete the mechanism to show the formation of one ester link in the first step of this reaction.

Mechanism

Suggest why chemists usually aim to design production methods

• with fewer steps

• with a high percentage atom economy.

High percentage atom economy

A two-step preparation of propylamine is shown.

bromoethane → X → propylamine

What is X ?

This question is about 2-bromopropane.

Define the term electronegativity.

Explain the polarity of the C–Br bond in 2-bromopropane.

Electronegativity

Draw the skeletal formula of the main organic species formed in the reaction between a large excess of 2-bromopropane and ammonia.

Give a use for the organic product.

Skeletal formula

This question is about amines.

Give an equation for the preparation of 1,6-diaminohexane by the reaction of 1,6-dibromohexane with an excess of ammonia.

Complete the mechanism for the reaction of ammonia with 6-bromohexylamine to form 1,6-diaminohexane.

Suggest the structure of a cyclic secondary amine that can be formed as a by-product in this reaction.

Mechanism

Cyclic secondary amine

1,6-Diaminohexane can also be formed in a two-stage synthesis starting from 1,4-dibromobutane. Suggest the reagent and a condition for each stage in this alternative synthesis.

Stage 1 reagent and condition

Stage 2 reagent and condition

Explain why 3-aminopentane is a stronger base than ammonia.

Justify the statement that there are no chiral centres in 3-aminopentane.

Which statement is correct about the molecule shown?

Figure 1 shows some compounds made from a halogenoalkane.

Draw the displayed formula of compound J.

Name the mechanism for Reaction 2 and give an essential condition used to ensure that CH₃CH₂CH₂NH₂ is the major product.

Name of mechanism

Calculate the mass, in grams, of CH₃CH₂CH₂NH₂ produced from 25.2 g of CH₃CH₂CH₂Br in Reaction 2 assuming a 75.0% yield.

Give your answer to the appropriate number of significant figures.

When Reaction 2 is carried out under different conditions, a compound with molecular formula C₉H₂₁N is produced. Draw the skeletal formula of the compound. Identify the functional group in the compound including its classification.

Skeletal formula

Identify the reagent and conditions used in Reaction 3.

Name and outline a mechanism for Reaction 3.

Name of mechanism

Mechanism

Amines E, F and G are weak bases.

Explain the difference in base strength of the three amines and give the order of increasing base strength.

Amine F can be prepared in a three-step synthesis starting from methylbenzene.

Suggest the structures of the two intermediate compounds.

For each step, give reagents and conditions only. Equations and mechanisms are not required.