This question is about the use of thin-layer chromatography (TLC) to investigate 1,2-dinitrobenzene and 1,4-dinitrobenzene, the structures of which are shown in the diagram below.

A solution of 1,4-dinitrobenzene was spotted onto a TLC plate coated with a polar solid, and the plate was run using hexane as the solvent. The diagram below shows the resulting chromatogram.

Use the chromatogram to determine the R_f value of 1,4-dinitrobenzene. Give your answer to 2 decimal places.

State what determines the distance travelled by a spot in TLC.

A second TLC experiment is carried out with 1,2-dinitrobenzene using the same conditions as before. The R_f value for 1,2-dinitrobenzene was calculated to be less than 1,4-dinitrobenzene.

State the relative polarities of 1,2-dinitrobenzene and 1,4-dinitrobenzene, and explain why 1,2-dinitrobenzene has a lower R_f.

A third TLC experiment is carried out with 1,2-dinitrobenzene using an identical TLC plate but using ethyl ethanoate as the solvent. 

Explain whether the R_f value would be greater or lower than in the experiment in part c).

This question is about ¹H NMR spectroscopy.

A compound is mixed with tetramethylsilane (TMS) and CDCl₃ before the ¹H NMR spectrum is obtained.

State and explain why TMS and CDCl₃ are used in NMR spectroscopy.

State the splitting pattern that would be observed in the ¹H NMR spectrum for each of the peaks given by the hydrogen atoms, labelled x, y and z, of the compound shown in the diagram below.

An isomer of the compound in part b) has only two singlet peaks in its ¹H NMR spectrum. The integration ratio is 2:9.

Draw the structure of this isomer.

The diagram below shows the structures of four isomers with the molecular formula C₆H₁₂O₂.

Identify which of the isomers shown in the diagram above would produce the ¹³C NMR spectrum shown below.

Justify your answer.

Identify which of the isomers shown in the diagram above would produce the ¹³C NMR spectrum shown below.

Justify your answer.

How many peaks would be observed in the ¹³C spectrum of 1,4-dimethylbenzene?

Gas chromatography is an analytical technique used to separate mixtures into their individual components.

Define the term retention time as applied to gas chromatography.

What is the role of the gas in gas chromatography?

Sketch a chromatogram on the axes below showing a mixture containing two components.

Explain how a gas chromatogram can be used to determine the percentage composition of each component in a mixture.

Organic compound X is analysed by a combination of techniques.

Elemental analysis:

C: 56.69%; H: 7.09%; N: 11.02%; O: 25.20%

Mass spectrum:

Molecular ion peak at m/z = 127.0

Use all the data to identify compound X explaining your reasoning.

Organic compound X is analysed by a combination of techniques.

Elemental analysis:

C: 73.17%; H: 7.32%; O: 19.51%

Mass spectrum:

Molecular ion peak at m/z = 164.0

Use all the data to identify compound X explaining your reasoning.

The diagram below shows the structure of an ester with four different carbon environments.

Complete the table below to predict the proton NMR spectrum of the ester.

Compound W is an isomer of the ester in part a). Compound W reacts with aqueous sodium carbonate and its ¹³C NMR spectrum has 4 peaks.

Draw a possible structure of compound W.

The diagram below shows the ¹H NMR spectrum of a compound known to be either propan-1-ol, propanal or propanoic acid.

Identify the compound from its proton NMR spectrum, justifying your answer.

The diagram below shows the structures of 2-nitrophenol, 3-nitrophenol and 4-nitrophenol.

Explain whether ¹³C NMR spectroscopy can be used to distinguish between these three compounds.

The diagram below shows the structure of the aromatic compound benzocaine.

Predict the number of peaks seen in the ¹³C NMR spectrum.

The diagram below shows the ¹H NMR spectrum of benzocaine dissolved in CDCl₃.

Explain why CDCl₃ was used as a solvent to obtain the NMR spectrum.

Complete the table below for the NMR data of benzocaine.

An organic compound is analysed using several techniques and the results are shown below.

Elemental analysis:

C: 54.54%; H: 9.10%; O: 36.36%

Mass spectrum:

Molecular ion peak at m/z = 132.0

When the NMR spectrum is run without D₂O, two additional peaks appear at chemical shifts of 11.0 and 3.6 ppm.

Determine the structure of the compound explaining your reasoning.

Organic compound X contains only carbon, hydrogen and nitrogen and is analysed by a combination of techniques.

Elemental analysis:

C: 74.17%; H: 11.41%; N: 14.42%

Mass spectrum:

Molecular ion peak at m/z = 97.0

Use all the data to identify compound X explaining your reasoning.