Organic reaction mechanisms

This question is about polymers.

A section of the polymer PVC is shown.

Name the monomer used to make PVC.

Draw the structure of the monomer used to make PVC.

Structure

State why PVC is not biodegradable.

Diisobutyl phthalate (DIBP) is a plasticiser added to PVC to modify its properties.

State how the properties of PVC are modified by the addition of DIBP.

An incomplete equation for the reaction used to make DIBP is shown.

Complete the equation.

Give the name of the mechanism for this reaction.

Deduce the empirical formula of DIBP.

Empirical formula of DIBP

A different plasticiser, DEHA, is added to PVC used for food packaging.

The structure of DEHA is

Identify the organic compound that would react with hexanedioic acid to form DEHA.

DEHA can be absorbed into food from PVC packaging.

In an investigation, 1 kg samples of three different foods are stored in PVC packaging for 30 days.

Table 1 shows the water content, fat content and mass of DEHA in each type of food after 30 days.

Use your knowledge of intermolecular forces to explain these results.

The polymer nylon 6,6 can be made from hexanedioyl dichloride and hexane-1,6-diamine.

Figure 2 shows an incomplete mechanism for the first steps in this reaction.

Draw the missing intermediate in the box in Figure 2.

Complete Figure 2 by adding the curly arrows and any relevant lone pairs of electrons involved in these steps in the mechanism.

The polymer nylon 6 can be made by heating caprolactam with water.

Figure 3 shows the species involved in the first three steps of the mechanism for this reaction.

Complete Figure 3 by adding the curly arrows and any relevant lone pairs of electrons involved in these steps in the mechanism.

Propanone reacts with bromine in alkaline conditions.

The rate equation for this reaction is

Sketch a graph on the axes provided to show how, at constant temperature, the concentration of bromine changes during this reaction.

Table 1 shows the initial rate of this reaction for experiments using different mixtures containing propanone, bromine and hydroxide ions.

Complete Table 1.

Use the data from experiment 1 to calculate the rate constant k for this reaction.

Give the units for the rate constant.

Figure 1 shows an incomplete mechanism for this reaction.

Complete the mechanism in Figure 1 by adding four curly arrows and any relevant lone pair(s) of electrons.

Use evidence from the rate equation to explain why Step 1 is the rate determining step.

This question is about ethanoic anhydride.

In the gas phase, ethanoic anhydride (CH₃CO)₂O decomposes to form ethenone.

The equation is

Ethenone is the simplest member of the ketene homologous series. Ketenes all contain one C=C double bond and one C=O double bond.

Deduce the general formula for the ketene homologous series.

Figure 11 shows an incomplete suggested mechanism for the decomposition of ethanoic anhydride.

Complete the mechanism in Figure 11 by adding three curly arrows and any relevant lone pairs of electrons.

For a chemical reaction the relationship between the rate constant, k, and the temperature, T, is shown by the Arrhenius equation.

For the decomposition of gaseous ethanoic anhydride

the activation energy, E_a = 34.5 kJ mol^–1

At temperature T₁ the rate constant, k = 2.48 10⁸ s^–1

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

Sketch the Maxwell–Boltzmann distribution of molecular energies for gaseous ethanoic anhydride at temperature T₁ and at a higher temperature T₂

Include a label for each axis, and mark on the appropriate axis a typical position for the activation energy.

Explain why the rate of reaction is faster at T₂

Explanation

This question is about esters.

Figure 4 shows an incomplete mechanism for the reaction of an ester with aqueous sodium hydroxide.

Add three curly arrows to complete the mechanism in Figure 4.

Name the type of reaction shown in Figure 4.

Deduce the role of the CH₃O⁻ ion in step 3 shown in Figure 4.

A triester in vegetable oil reacts with sodium hydroxide in a similar way.

Give a use for a product of this reaction.

This question is about fuels.

The petrol fraction obtained from crude oil can be used as fuel in cars.

State the meaning of fraction, as used in the term petrol fraction.

Hexadecane (C₁₆H₃₄) can be cracked at high temperature to form petrol.

Complete the equation to show the cracking of one molecule of hexadecane to form hexane and cyclopentane only.

Give the name of a catalyst used in this cracking reaction.

Carbon dioxide is formed when petrol is burned. Carbon dioxide acts as a greenhouse gas when it absorbs infrared radiation.

Give a reason why carbon dioxide absorbs infrared radiation.

Compound Z (HOCH₂CH₂NH₂) can be used to remove carbon dioxide from the mixture of waste gases produced in some power stations.

Figure 1 shows part of a suggested mechanism for the reaction of Z with carbon dioxide.

Draw two curly arrows to complete the mechanism in Figure 1.

Name compound Z (HOCH₂CH₂NH₂)

Deduce the role of Z in step 2 of the mechanism.

HOCH₂CH₂NH₂ can be represented as XNH₂ [HOCH₂CH₂NH₃]⁺ can be represented as [XNH₃]⁺

Draw the shape of XNH₂ and of [XNH₃]⁺

State whether the H–N–H bond angle in XNH₂ is greater than, the same as, or smaller than that in [XNH₃]⁺

Explain your answer.

Shape of XNH₂ Shape of [XNH₃]⁺

Bioethanol is used as an alternative to fossil fuels.

This statement appeared on a website.

“The fact that bioethanol is a carbon-neutral fuel outweighs the environmental disadvantages of producing bioethanol.”

Evaluate this statement.

In your answer you should include:

• an outline of how bioethanol is produced

• relevant equations

• analysis of the environmental impacts.

This question is about the ozone layer in the upper atmosphere.

State why the ozone layer is beneficial for living organisms.

State how chlorofluorocarbons (CFCs) form chlorine atoms in the upper atmosphere.

Give equations to show how chlorine atoms catalyse the decomposition of ozone.

Hydrochlorofluorocarbons (HCFCs) have been used in place of CFCs. In the mechanism to make an HCFC from a fluoroalkane, two incomplete steps are shown.

Complete each step in the mechanism.

Give the name of the type of step shown by both these equations.

A and B react together to form an equilibrium mixture.

An aqueous solution containing 0.25 mol of A is added to an aqueous solution containing 0.25 mol of B.

When equilibrium is reached, the mixture contains 0.015 mol of C.

Calculate the amount of A and the amount of B, in moles, in the equilibrium mixture.

At a different temperature, another equilibrium mixture contains 0.30 mol of A, 0.25 mol of B and 0.020 mol of C in 350 cm³ of solution.

Calculate the value of the equilibrium constant K_c

When an excess of water is added to chloroethanal, an equilibrium mixture is formed.

An expression for an equilibrium constant (K) for the reaction under these conditions is

Suggest why an expression for K can be written without the concentration of water.

Distilled water is added to 4.71 g of chloroethanal (M_r = 78.5) to make 50.0 cm³ of solution. The mixture is allowed to reach equilibrium.

The value of the equilibrium constant (K) is 37.0

Calculate the equilibrium concentration, in mol dm^–3, of ClCH₂CH(OH)₂

When an excess of water is added to ethanal a similar nucleophilic addition reaction occurs.

Suggest why this reaction is slower than the reaction in Question 09.5.