Naming organic compounds

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

This question is about rapeseed oil.

Figure 2 shows the structure of compound Q found in rapeseed oil. Each branch in the molecule is formed from a different long-chain carboxylic acid.

State the type of stereoisomerism shown in Branch A.

Q can be reacted with methanol to form three different esters.

State the number used to identify the position of the C=C bond in the name of the ester formed from Branch A.

State the number of different stereoisomers of the ester formed from Branch B.

Give a use for these esters.

Number used in the name of the ester

Number of stereoisomers

Q also reacts with NaOH

State the formula of the product, formed by Branch B in Figure 2, in this reaction.

State a use for this product.

What is the correct structural formula for 4-chloro-2-methylpent-2-enoic acid?

This question is about the preparation of an ester.

Ester F can be prepared from propan-2-ol and ethanoic acid.

Give an equation for this reaction.

Name ester F.

Equation

This method is used to prepare a sample of ester F.

Step 1 Mix 10 cm³ of propan-2-ol with 10 cm³ of ethanoic acid. Add 5 drops of concentrated sulfuric acid. Reflux this reaction mixture for 20 minutes.

Step 2 Transfer the cooled reaction mixture to a separating funnel. Add 20 cm³ of aqueous sodium carbonate and shake the mixture.

Step 3 Transfer the organic layer to a beaker and add 5 g of anhydrous magnesium sulfate. Decant off the organic liquid.

Step 4 Collect the ester using simple distillation.

Describe how Step 1 should be done.

In your description you should

• give details of suitable equipment used to add each reagent to the reflux apparatus

• draw a labelled diagram of the apparatus used for refluxing the reaction mixture

• explain any safety precautions needed other than eye protection.

In Step 2 the reaction mixture from Step 1 is shaken with aqueous sodium carbonate.

State the purpose of the sodium carbonate.

Suggest a precaution that should be taken while this mixture is shaken in the separating funnel.

Give a reason for your suggested precaution.

Purpose of sodium carbonate

Suggest how the purity of the ester can be confirmed during the distillation in Step 4.

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.

The thermal decomposition of but-3-en-1-ol is investigated at different temperatures (T).

CH₂=CHCH₂CH₂OH → CH₂=CHCH₃ + HCHO

The results from the investigation are used to calculate the rate constant, k, at each temperature.

Table 2 shows some of the results.

Complete Table 2 with the missing values at 573 K

The overall order of the reaction can be deduced from a piece of information in one of the column headings in Table 2.

Identify this piece of information and deduce the overall order.

Piece of information

The Arrhenius equation can be written in the form shown.

On the grid in Figure 3 plot a graph of ln k against

Use your graph from Question 03.3 to calculate a value for E_a, in kJ mol^–1, for the thermal decomposition of but-3-en-1-ol.

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

2-Methylpent-4-en-2-ol decomposes in a similar way to but-3-en-1-ol, to produce an alkene and a carbonyl compound.

Deduce the structures of the alkene and the carbonyl compound.

alkene
carbonyl compound

What is the correct structural formula for 4-chloro-2-methylpent-2-enoic acid?

What is the product when 3-methylbutan-2-one reacts with acidified KCN?

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.

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

Endomorphin - 2 is a peptide with the amino acid sequence shown.

Tyr–Pro–Phe–Phe–NH₂

Each amino acid is represented by a three-letter abbreviation.

Tyr = tyrosine Pro = proline Phe = phenylalanine

Figure 2 shows part of the structure of endomorphin - 2, showing the Tyr–Pro–Phe– part of the molecule.

The –NH₂ at the end of the amino acid sequence of endomorphin-2 shows that the terminal functional group is an amide, not an acid.

Complete the structure of endomorphin-2 in Figure 2.

Use the structure in Figure 2 to draw the skeletal formula of proline, Pro.

A student hydrolyses a sample of endomorphin - 2 to break it down into its constituent amino acids.

The student analyses the resulting mixture by thin-layer chromatography, TLC.

State a reagent and the conditions needed for the hydrolysis.

Figure 3 shows the apparatus used for the TLC.

There is a piece of the apparatus missing from Figure 3. This omission will result in an inaccurate chromatogram.

Identify the missing piece of the apparatus.

State and explain why this piece of the apparatus is needed.

State why the amino acids separate on the TLC plate.

When the solvent has risen up the TLC plate, the student removes the plate from the beaker and sprays it with a developing agent.

Figure 4 shows the result.

Name a suitable developing agent.

State why the developing agent is needed.

Determine the R_f value for Tyr.

An acidified solution of butanone reacts with iodine as shown.

Draw the displayed formula for CH₃CH₂COCH₂I

Give the name of CH₃CH₂COCH₂I

Displayed formula

The rate equation for the reaction is

Table 1 shows the initial concentrations used in an experiment.

The initial rate of reaction in this experiment is 1.45×10⁻⁴ mol dm⁻³ s⁻¹

Calculate the value of the rate constant, k, for the reaction and give its units.

Calculate the initial rate of reaction when all of the initial concentrations are halved.

An experiment was done to measure the time, t, taken for a solution of iodine to react completely when added to an excess of an acidified solution of butanone.

Suggest an observation used to judge when all the iodine had reacted.

The experiment was repeated at different temperatures. Figure 1 shows how varied with temperature for these experiments.

Describe and explain the shape of the graph in Figure 1.

Deduce the time taken for the reaction at 35^oC

For a different reaction, Table 2 shows the value of the rate constant at different temperatures.

This equation can be used to calculate the activation energy, E_a

Calculate the value, in kJ mol⁻¹, of the activation energy, E_a

The gas constant, R = 8.31 J K⁻¹mol⁻¹

Name and outline the mechanism for the reaction of butanone with KCN followed by dilute acid.

Name of mechanism

Outline of mechanism

Which compound is not a 2-aminocarboxylic acid?

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.

Which statement about (CH₃)₂CHCH₂COOH is correct?

Which is the correct general formula for non-cyclic compounds in the homologous series?

This question is about citric acid, a hydrated tricarboxylic acid. Its formula can be

A 1.50 g sample of H₃Y.H₂O contains 0.913 g of oxygen by mass. The sample burns completely in air to form 1.89 g of CO₂ and 0.643 g of H₂O

Show that the empirical formula of citric acid is C₃H₅O₄

A 3.00 g sample of H₃Y.H₂O (M_r = 210.0) is heated to constant mass. The anhydrous H₃Y that remains has a mass of 2.74 g

Show, using these data, that the value of = 1

Figure 5 shows the structure of H₃Y

Complete this IUPAC name for H₃Y

State the number of peaks you would expect in the¹³C NMR spectrum for H₃Y

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.

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.

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.

Give the IUPAC name of CH₃CH₂CH₂CH₂CH(OH)CN

Describe how you would distinguish between separate samples of the two

Explain why the reaction produces a racemic mixture.

An isomer of CH₃CH₂CH₂CH₂CHO reacts with KCN followed by dilute acid to form a compound that does not show stereoisomerism.

Draw the structure of the compound formed and justify why it does not show stereoisomerism.

Structure

Justification

This question is about amino acids and peptide (amide) links.

Draw the structure of the zwitterion formed by phenylalanine.

Draw the structure of serine at high pH.

Draw the structures of both dipeptides formed when phenylalanine reacts with serine.

In each structure show all the atoms and bonds in the amide link.

An amide link is also formed when an acyl chloride reacts with a primary amine.

Name and outline a mechanism for the reaction between CH₃CH₂COCl and

Give the IUPAC name of the organic product.

Name of mechanism

Mechanism

IUPAC name of organic product

Give the full IUPAC name of isomer P.

A sample of P was mixed with an excess of oxygen and the mixture ignited. After cooling to the original temperature, the total volume of gas remaining was

When this gas mixture was passed through aqueous sodium hydroxide, the carbon dioxide reacted and the volume of gas decreased to 155 cm³

Both gas volumes were measured at 25 °C and 105 kPa

Write an equation for the combustion of P in an excess of oxygen and calculate the mass, in mg, of P used.

The gas constant R = 8.31 J K⁻¹ mol⁻¹

Mass of P used mg

Isomer Q (C₆H₁₀O₂) is a cyclic compound. The infrared spectrum of Q is shown in Figure 4 and the¹³C NMR spectrum of Q is shown in Figure 5.

Use these spectra and Tables A and C in the Data Booklet to deduce the structure of Q. In your answer, state one piece of evidence you have used from each spectrum.

Structure of Q.

Evidence from Figure 4

Evidence from Figure 5

Isomers R and S are shown.

Although the¹³C spectra of R and S both show the same number of peaks, the spectra can be used to distinguish between the isomers.

Justify this statement using Table C from the Data Booklet.

Give the number of peaks for each isomer.

Justification

Although the¹H spectra of R and S both show the same number of peaks, the spectra can be used to distinguish between the isomers.

Justify this statement using the splitting patterns of the peaks.

Give the number of peaks for each isomer.

Justification

The action of heat on 5-hydroxyhexanoic acid can lead to two different products.

On gentle heating, 5-hydroxyhexanoic acid loses water to form a cyclic

Under different conditions, 5-hydroxyhexanoic acid forms a polyester.

Draw the structure of T.

Draw the repeating unit of the polyester and name the type of polymerisation.

Structure of T

Repeating unit of polyester

Type of polymerisation

Isomer U is shown.

The polymer formed by U and the polymer formed by 5-hydroxyhexanoic acid in Question 10.6 both contain ester groups that can be hydrolysed.

Draw the repeating unit of the polymer formed by U.

Justify the statement that, although both polymer structures contain ester groups, the polymer formed by U is not biodegradable.

Repeating unit of polymer formed by U.

Justification