Electrophilic addition

This question is about different ways to make 1,2-dichlorobutane.

Give the name of the mechanism for reaction 1.

State one essential condition needed for reaction 1.

Name of mechanism

Essential condition

Give equations to show three essential steps in the mechanism for reaction 1.

Suggest two reasons why using reaction 1 is likely to give a low yield of 1,2-dichlorobutane.

Give a suitable reagent and conditions needed for reaction 2.

Identify the reagent and name the mechanism for reaction 3.

Name of mechanism

Use of the reagent for reaction 2 followed by the reagent for reaction 3 gives another organic product.

Give the structure of the other organic product.

This question is about isomerism.

Compound L has this structure.

Use IUPAC rules to name L.

Explain why L exists as stereoisomers.

Compound M has the same carbon chain as L but the double bond is in a different position.

M also exists as stereoisomers.

Draw the structural formula of M.

Explain why M exists as stereoisomers.

Structural formula

Figure 1 shows part of the mechanism when L reacts with hydrogen bromide.

Complete Figure 1 to show the next step in the mechanism that gives the

Compound X reacts with concentrated sulfuric acid to produce compound Y.

Compound Y reacts with an excess of water to produce an alcohol.

Which compound could be X ?

The hydration of 1-methylcyclopent-1-ene uses a catalyst of sulfuric acid and produces a mixture of products.

Which ion is formed during the mechanism for this reaction to give the major product?

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

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.

A student plans a series of chemical tests to confirm the identities of four organic

This is the student’s method.

To separate test tubes containing samples of each liquid:

Test 1 add potassium dichromate(VI) solution and warm gently

Test 2 add Fehling’s solution and cool in iced water

Test 3 add sodium hydrogencarbonate solution and test any gas produced with a lighted splint

Test 4 add bromine water and shake at room temperature.

Identify the missing reagent needed in Test 1.

In addition to the missing reagent in Test 1, there is a mistake in the method for two of the other tests.

State the two mistakes.

Suggest how each of the mistakes should be corrected.

The missing reagent is added and the mistakes are corrected.

Identify the liquid(s), J, K, L and M, that would react in each test.

State the expected observation for each reaction.

Liquid(s) that react in Test 1

Expected observation

Liquid(s) that react in Test 2

Expected observation

Liquid(s) that react in Test 3

Expected observation

Liquid(s) that react in Test 4

Expected observation

Figure 10 shows the apparatus that is used to separate a mixture of liquids K and M using fractional distillation.

Suggest labels that should be added to positions S, T and U in Figure 10.

Explain why fractional distillation is preferred to simple distillation to separate liquids K and M.

Compound X can be converted into an alcohol in a two-stage process.

What is the name of compound X ?

This question is about 2-methylbut-1-ene.

Name the mechanism for the reaction of 2-methylbut-1-ene with concentrated sulfuric acid.

Outline the mechanism for this reaction to form the major product.

Outline of mechanism to form major product

Draw the structure of the minor product formed in the reaction in Question 03.1

Explain why this is the minor product.

Structure of minor product

Draw the skeletal formula of a functional group isomer of 2-methylbut-1-ene.

2-methylbut-1-ene can form a polymer.

State the type of polymerisation.

Draw the repeating unit for the polymer formed.

Type of polymerisation

Repeating unit

This question is about the preparation of hexan-2-ol. Hexan-2-ol does not mix with water and has a boiling point of 140^oC

Hexan-2-ol can be prepared from hex-1-ene using this method.

a Measure out 11.0 cm³ of hex-1-ene into a boiling tube in an ice bath. b Carefully add 5 cm³ of concentrated phosphoric acid to the hex-1-ene. c After 5 minutes add 10 cm³ of distilled water to the mixture and transfer the boiling tube contents to a separating funnel.

d Shake the mixture and allow it to settle. e Discard the lower (aqueous) layer. f Add a fresh 10 cm³ sample of distilled water and repeat steps d and e. g Transfer the remaining liquid to a beaker. h Add 2 g of anhydrous magnesium sulfate and allow to stand for 5 minutes. i Filter the mixture under reduced pressure. j Distil the filtrate and collect the distillate that boils in the range 130–160^oC

It is important to wear eye protection and a lab coat when completing this experiment.

Suggest, with a reason, one other appropriate safety precaution for this experiment.

Give a reason for adding the distilled water in steps c and f.

Give a reason for adding anhydrous magnesium sulfate in step h.

Complete and label the diagram of the apparatus used to filter the mixture under reduced pressure in step i.

Identify the most likely organic impurity, other than hex-1-ene, in the distillate collected in step j.

Suggest one reason why it could be difficult to remove this impurity.

Calculate the mass, in g, of hexan-2-ol formed from 11.0 cm³ of hex-1-ene if the yield is 31.0%

Give your answer to 1 decimal place.

Density of hex-1-ene = 0.678 g cm⁻³

This question is about olive oil.

A sample of olive oil is mainly the unsaturated fat Y mixed with a small amount of inert impurity.

The structure of Y in the olive oil is shown. Y has the molecular formula C₅₇H₁₀₀O₆ (M_r = 880).

The amount of Y is found by measuring how much bromine water is decolourised by a sample of oil, using this method.

• Transfer a weighed sample of oil to a 250 cm³ volumetric flask and make up to the mark with an inert organic solvent.

• Titrate 25.0 cm³ samples of the olive oil solution with 0.025 mol dm⁻³ Br₂(aq).

A suitable target titre for the titration is 30.0 cm³ of 0.025 mol dm⁻³ Br₂(aq).

Justify why a much smaller target titre would not be appropriate.

Calculate the amount, in moles, of bromine in the target titre.

Calculate a suitable mass of olive oil to transfer to the volumetric flask using your answer to Question 09.1 and the structure of Y. Assume that the olive oil contains 85% of Y by mass.

(If you were unable to calculate the amount of bromine in the target titre, you should assume it is 6.25×10⁻⁴ mol. This is not the correct amount.)

The olive oil solution can be prepared using this method.

• Place a weighing bottle on a balance and record the mass, in g, to 2 decimal places.

• Add olive oil to the weighing bottle until a suitable mass has been added.

• Record the mass of the weighing bottle and olive oil.

• Pour the olive oil into a 250 cm³ volumetric flask.

• Add organic solvent to the volumetric flask until it is made up to the mark.

• Place a stopper in the flask and invert the flask several times.

Suggest an extra step to ensure that the mass of olive oil in the solution is recorded accurately.

Justify your suggestion.

State the reason for inverting the flask several times.

A sample of the olive oil was dissolved in methanol and placed in a mass spectrometer. The sample was ionised using electrospray ionisation. Each molecule gained a hydrogen ion (H⁺) during ionisation. The spectrum showed a peak for an ion with = 345 formed from an impurity in the olive oil. The ion with = 345 was formed from a compound with the empirical formula C₅H₁₀O

Deduce the molecular formula of this compound.

Show your working.

Molecular formula 12

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

Which compound decolourises bromine water in the absence of sunlight?

Which compound reacts with hydrogen bromide to give 2-bromo-3-methylbutane as the major product?

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.

Which alkene reacts with hydrogen bromide to give 2-bromo-3-methylbutane as the major product?

Cyclohexene (boiling point = 83 °C) can be prepared by the dehydration of cyclohexanol (boiling point = 161 °C) using concentrated phosphoric acid.

A student prepared cyclohexene by placing 10 cm³ of cyclohexanol (density = 0.96 g cm^–3) into a round-bottomed flask. 3 cm³ of concentrated phosphoric acid were then carefully added to the flask. The student added a few anti-bumping granules and set up the apparatus shown in Figure 3.

• The student heated the mixture and collected the liquid that distilled at temperatures below 100 °C

• The distillate was poured into a separating funnel and washed by shaking with sodium carbonate solution.

• Periodically, the separating funnel was inverted and the tap opened.

• The aqueous layer was discarded and the final organic product was dried using anhydrous calcium chloride.

• After the product was dried, the drying agent was removed by filtration under reduced pressure.

The student collected 5.97 g of cyclohexene in the experiment.

Calculate the percentage yield of cyclohexene.

Describe a test-tube reaction, on the product, to show that the cyclohexanol had been dehydrated. State what you would observe.

Suggest why sodium carbonate solution was used to wash the distillate.

Explain why it is important to open the tap of the separating funnel periodically.

Give a property of anhydrous calcium chloride, other than its ability to absorb water, that makes it suitable as a drying agent in this preparation.

Describe the apparatus used to remove the drying agent by filtration under reduced pressure. Your description of the apparatus can be either a labelled diagram or a description in words.

A sample of cyclohexene has been contaminated with cyclohexanol. The cyclohexene can be separated from the cyclohexanol by column chromatography. Silica gel is used as the stationary phase and hexane as the mobile phase.

Explain why cyclohexene has a shorter retention time than cyclohexanol.

Explain how an infrared spectrum would confirm that the cyclohexene obtained from the chromatography column did not contain any cyclohexanol.