AQA A Level Chemistry Paper 2 June 2019 question paper 7405/2

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.

A student prepared cyclohexene by heating cyclohexanol with concentrated phosphoric acid. The cyclohexene produced was distilled off from the reaction mixture.

Complete the diagram of the apparatus used to distil the cyclohexene from the reaction mixture at 83 °C.

The distillate was shaken with saturated sodium chloride solution. The cyclohexene was separated from the aqueous solution using a separating funnel.

State why cyclohexene can be separated from the aqueous solution using the separating funnel.

The cyclohexene separated in Question 02.2 was obtained as a cloudy liquid. The student dried this cyclohexene by adding a few lumps of anhydrous calcium chloride and allowing the mixture to stand.

Give one observation that the student made to confirm that the cyclohexene was dry.

In this preparation, the student added an excess of concentrated phosphoric acid to

Calculate the percentage yield of cyclohexene obtained. Give your answer to the appropriate number of significant figures.

Cyclohexene reacts with bromine.

Complete the mechanism for this reaction.

The outer layers of some golf balls are made from a polymer called polyisoprene. The isoprene monomer is a non-cyclic branched hydrocarbon that contains 88.2 % carbon by mass. The empirical formula of isoprene is the same as its molecular formula.

Deduce the molecular formula of isoprene and suggest a possible structure.

Molecular formula

Structure

The insides of some golf balls are made from a mixture of three other polymers. The repeating unit for one of these polymers is shown.

Draw the skeletal formula of the monomer used to make this polymer.

Give the IUPAC name of the monomer.

Skeletal formula of monomer

A second polymer in the mixture has a repeating unit with the structure shown.

The third polymer in the mixture is a stereoisomer of this polymer.

Draw the structure of the repeating unit of the third polymer.

Give a reason why this type of stereoisomerism arises.

Repeating unit

Golf balls recovered from lakes and ponds can be used again even after being in water for several years.

Explain why these golf balls do not biodegrade.

Substances P and Q react in solution at a constant temperature. The initial rate of reaction was studied in three experiments by measuring the change in concentration of P over the first five seconds of the reaction. The data obtained are shown in Table 1.

Complete Table 2 to show the initial rate of reaction of P in each experiment.

Determine the order of reaction with respect to P and the order of reaction with respect to Q.

A reaction between substances R and S was second order with respect to R and second order with respect to S. At a given temperature, the initial rate of reaction was 1.20 × 10^–3 mol dm^–3 s^–1 when the initial concentration of R was 1.00 × 10^–2 mol dm^–3 and the initial concentration of S was 2.45 × 10^–2 mol dm^–3

Calculate a value for the rate constant, k, for the reaction at this temperature. Give the units for k

The rate constant, k, for a reaction varies with temperature as shown by the equation

For this reaction, at 25 °C, k = 3.46 × 10⁸ s¹ The activation energy E_a = 96.2 kJ mol¹ The gas constant R = 8.31 J K¹ mol¹

Calculate a value for the Arrhenius constant, A, for this reaction. Give the units for A.

This question is about isomers.

Give a reagent and observations for a test-tube reaction to distinguish between 2-methylbutan-1-ol and 2-methylbutan-2-ol.

Observation with 2-methylbutan-1-ol

Observation with 2-methylbutan-2-ol

Compounds A and B both have the molecular formula C₄H₈Br₂ A has a singlet, a triplet and a quartet in its¹H NMR spectrum. B has only two singlets in its¹H NMR spectrum.

Draw a structure for each of A and B.

A B

Compounds C and D both have the molecular formula C₆H₃Br₃ C has two peaks in its¹³C NMR spectrum. D has four peaks in its¹³C NMR spectrum.

Draw a structure for each of C and D

C D

Compounds E, F, and G are isomers.

Figure 1 shows the infrared spectra of these isomers, but not necessarily in the same order.

Label each spectrum with the correct letter E, F or G in the box.

Isomers X and Y have the molecular formula C₅H₈O

Give the IUPAC name for isomer X.

Explain how and why isomers X and Y can be distinguished by comparing each of their

• boiling points

•¹³C NMR spectra

• infrared spectra.

Use data from Tables A and C in the Data Booklet in your answer.

Paracetamol is a medicine commonly used to relieve mild pain. Traditionally, paracetamol has been made industrially in a three-step synthesis from

Name the mechanism of the reaction in Step 1.

Complete the equation for the reaction in Step 2.

In theory, either ethanoyl chloride or ethanoic anhydride could be used in Step 3.

Complete the mechanism for the reaction of 4-aminophenol with ethanoyl chloride. RNH₂ is used to represent 4-aminophenol in this mechanism.

In practice, ethanoic anhydride is used in the industrial synthesis rather than ethanoyl chloride.

Give one reason why ethanoyl chloride is not used in the industrial synthesis.

In Step 3 other aromatic products are formed as well as paracetamol.

Draw the structure of one of these other aromatic products.

Chemists have recently developed a two-step process to produce paracetamol from phenol. In the first step, phenol is oxidised to hydroquinone.

In the second step, hydroquinone reacts with ammonium ethanoate to form paracetamol.

Complete the equation for this second step.

Calculate the mass, in kg, of hydroquinone (M_r = 110.0) needed to produce 250 kg of paracetamol.

This question is about thin-layer chromatography (TLC).

• A protein was hydrolysed to form a mixture of amino acids.

• A spot of this mixture was added to a TLC plate and the plate placed vertically in a small volume of solvent 1.

• When the solvent front reached nearly to the top of the plate, the plate was removed and allowed to dry.

• The plate was turned anticlockwise through 90° and placed vertically in a small volume of solvent 2.

• When the solvent front reached nearly to the top of the plate, the plate was again removed and allowed to dry.

• Figure 2 shows the final TLC plate.

Suggest a suitable reagent for the hydrolysis of a protein.

Suggest how the positions of the amino acids on the TLC plate were located.

Deduce the minimum number of amino acids present in the original mixture.

Suggest why it was necessary to use two different solvents.

Some compounds with different molecular formulas have the same relative molecular mass to the nearest whole number.

A dicarboxylic acid has a relative molecular mass of 118, to the nearest whole number.

Deduce the molecular formula of the acid.

Molecular formula

A student dissolved some of the dicarboxylic acid from Question 10.1 in water and made up the solution to 250 cm³ in a volumetric flask. In a titration, a 25.0 cm³ sample of the acid solution needed 21.60 cm³ of 0.109 mol dm³ sodium hydroxide solution for neutralisation.

Calculate the mass, in g, of the dicarboxylic acid used. Give your answer to the appropriate number of significant figures.

Compounds with molecular formula C₆H₁₄O₂ also have a relative molecular mass of 118 to the nearest whole number. These include the diol shown.

Deduce the number of peaks in the¹H NMR spectrum of this diol.

Draw the structure of a different diol also with molecular formula C₆H₁₄O₂ that has a ¹H NMR spectrum that consists of two singlet peaks.

The dicarboxylic acid in question 10.1 and the isomers of C₆H₁₄O₂ in Questions 10.3 and 10.4 all have a relative molecular mass of 118

State why the dicarboxylic acid can be distinguished from the two diols by high resolution mass spectrometry using electrospray ionisation.

This question is about esters including biodiesel.

An ester is formed by the reaction of an acid anhydride with CH₃CH₂OH

Complete the equation. In your answer show clearly the structure of the ester. Give the IUPAC name of the ester.

In a reaction to form biodiesel, one mole of a vegetable oil reacts with an excess of methanol to form two moles of an ester with molecular formula C₁₉H₃₄O₂ and one mole of an ester with molecular formula C₁₉H₃₆O₂

Draw the structure of the vegetable oil showing clearly the ester links.

You should represent the hydrocarbon chains in the form C_xH_y where x and y are the actual numbers of carbon and hydrogen atoms.

The compound C₁₉H₃₄O₂ is the methyl ester of Z,Z-octadeca-9,12-dienoic acid.

Part of the structure of the acid is shown.

Complete the skeletal formula to show the next part of the hydrocarbon chain to carbon atom number 14. In your answer, show the Z stereochemistry around both C=C double bonds.

Give an equation for the complete combustion of the ester C₁₉H₃₄O₂

Combustion of biodiesel produces greenhouse gases such as carbon dioxide that cause global warming. Part of the infrared spectrum of carbon dioxide is shown in Figure 3.

State how the infrared spectrum of carbon dioxide in Figure 3 is not what you might predict from the data provided in Table A in the Data Booklet.

Explain how carbon dioxide causes global warming.

Figure 4 shows two complementary strands in part of a DNA double helix structure.

Draw all the hydrogen bonds between the complementary strands shown in Figure 4.

Use dashed lines to show the hydrogen bonds. You do not need to show lone pairs of electrons or partial charges.

Draw a ring around each of the component parts that make up the cytosine nucleotide in the section of DNA shown in Figure 4.

State the meaning of the term complementary when it is used to refer to DNA strands.

Aqueous NaBH₄ reduces aldehydes but does not reduce alkenes.

Show the first step of the mechanism of the reaction between NaBH₄ and 2-methylbutanal. You should include two curly arrows.

Explain why NaBH₄ reduces 2-methylbutanal but has no reaction with 2-methylbut-1-ene.

First step of mechanism

A student attempted to reduce a sample of 2-methylbutanal but added

Give the reagent and observation for the chemical test.