Infrared spectroscopy

This question is about spectroscopy.

Compound P is a hydrocarbon with only one peak (a singlet) in its¹H NMR spectrum.

Carbon has a precise A_r of 12.00000

Hydrogen has a precise A_r of 1.00783

Use this information to deduce the molecular formula of P. Show your working.

Suggest two possible structures for P.

Explain how P can be identified using its infrared spectrum above 1500 cm^–1

Use Table A in the Data Booklet to help you to answer this question.

Molecular formula

Structure 1

Structure 2

Compound Q has the molecular formula C₅H₈O₂

Figure 7 shows the¹³C NMR spectrum of compound Q.

Figure 8 shows the¹H NMR spectrum of compound Q.

Explain what you can deduce about the structure of compound Q.

In your answer you should refer to

• the peaks in the¹³C NMR spectrum

• the chemical shift values for the peaks in the¹H NMR spectrum

• the splitting pattern for the peaks in the¹H NMR spectrum.

Give the structure of compound Q.

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This question is about oxidation.

A student has separate unlabelled samples of propan-1-ol and propan-2-ol but does not know which sample is which alcohol.

The student plans a series of steps to identify the alcohols.

Step 1 Oxidise each sample, distilling off the organic product as it is formed. Step 2 Identify the organic products using a simple chemical test. Step 3 Confirm the identities using the infrared spectrum of each original sample.

Give further details of each step in the plan. In your answer include

• an appropriate oxidising agent used in Step 1

• equations, using [O] to represent the oxidising agent, for each reaction in Step 1

• a suitable test and expected observations in Step 2

• how the infrared spectra can be used to confirm the identities.

A primary alcohol can be oxidised to form a carboxylic acid using an excess of the oxidising agent in Question 05.1.

Give the condition needed for this reaction.

Complete the diagram, adding labels, to show how the apparatus would be set up.

During oxidation reactions, anti-bumping granules are often added to the pear-shaped flask containing the reactants.

State why anti-bumping granules are used.

This question is about compound Z, with molecular formula C₇H₁₂O₃

Figure 7 shows the infrared spectrum of Z.

Identify the bond that causes the absorption at 1725 cm^–1

Figure 8 shows the¹³C NMR spectrum of Z.

How many different carbon environments are there in a molecule of Z ?

State the type of carbon environment that causes the peak at = 174 ppm

Use Table C in the Data Booklet to help you answer this question.

Table 2 shows data from the¹H NMR spectrum for compound Z.

Explain what can be deduced from the splitting patterns and chemical shift values for the peaks at = 4.10 ppm and at = 1.26 ppm

Deduce the part of the structure of Z that causes the peaks at

Use Table B in the Data Booklet to help you answer this question.

Peak at = 1.26 ppm

Part of structure

Deduce the part of the structure of Z that causes the peak at = 2.19 ppm

Part of structure

Figure 9 shows the¹H NMR spectrum of compound Z.

Suggest why it would be difficult to determine the structure of Z using the spectrum in Figure 9, without the information in Table 2 on page 13.

Deduce the structure of Z.

The skeletal formulas of two compounds are shown.

Which method would distinguish between samples of these compounds?

This question is about compound X with the empirical formula C₂H₄O

Figure 2 shows the infrared spectrum of X.

Figure 3 shows the¹³C NMR spectrum of X.

The¹H NMR spectrum of X shows four peaks with different chemical shift values. Table 3 gives data for these peaks.

Show how information from Figure 2, Figure 3 and Table 3 can be used to deduce the structure of compound X.

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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 spectroscopy.

Compound K has molecular formula C₄H₈O Figure 5 shows the infrared spectrum of K.

Which functional group does K contain?

Tick (✓) one box.

Compound L has molecular formula C₄H₇NO Figure 6 shows the infrared spectrum of L.

L reacts with H₂ in the presence of a nickel catalyst to give compound M.

Suggest three ways in which the infrared spectrum of M is different from the infrared spectrum of L.

Figure 7 shows the¹H NMR spectrum of Q, C₃H₇ClO

Table 4 shows the chemical shifts (δ values) and integration values for each peak.

Explain your answer.

Which statement does not support the suggestion that an unknown organic

This question is about the structural isomers shown.

Identify the isomer(s) that would react when warmed with acidified potassium dichromate(VI).

State the expected observation when acidified potassium dichromate(VI) reacts.

Expected observation

State the type of structural isomerism shown by isomers P, Q, R and S.

Describe fully how infrared spectra can be used to distinguish between isomers R, S and T. Use data from Table A in the Data Booklet in your answer.

State why mass spectrometry using electrospray ionisation is not a suitable method to distinguish between the isomers.

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.

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.

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.

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