Instrumental methods

This question is about spectral analysis.

Compound K, C₄H₁₀O, is refluxed with H₂SO₄ to form a mixture of compound L and compound M.

The infrared spectrum of compound K is shown.

Compound L and compound M are analysed using¹³C NMR spectroscopy.

• The¹³C NMR spectrum of compound L has 4 peaks.

• The¹³C NMR spectrum of compound M has 2 peaks.

Suggest the functional group in compound K, showing your reasoning, and suggest possible structures for compound K, compound L and compound M.

Functional group........

* An unknown organic compound N is analysed and produces the following results.

Elemental analysis by mass

C, 62.07%; H, 10.34%; O, 27.59%

Mass spectrum

The numbers by the peaks are the relative peak areas.

Determine the structure of the compound N, showing all your reasoning.

23* An unknown organic compound is analysed.

The results are shown below.

Addition of 2,4-DNP No visible change

Elemental analysis by mass C, 66.63%; H, 11.18%; O, 22.19%

Mass spectrum Molecular ion peak at m / z = 144.0

IR spectrum

Proton NMR spectrum The numbers by each peak are the relative peak areas.

Use the information to identify the organic compound.

Show all your reasoning.

This question is about unsaturated hydrocarbons.

What is the systematic name of hydrocarbon A ?

Compounds B and C are branched hydrocarbons that are structural isomers of C₆H₁₂.

Compounds B and C both have stereoisomers.

• Compound B has cis and trans isomers but does not have optical isomers.

• Compound C has optical isomers but does not have cis and trans isomers.

What is meant by the term structural isomers ?

What is meant by the term stereoisomers ?

Draw structures for the cis and trans isomers of the branched hydrocarbon B.

Draw 3D structures for the optical isomers of compound C.

Compounds D and E are two more structural isomers of C₆H₁₂.

Compounds D and E do not show stereoisomerism.

Table 16.1 shows NMR and infrared (IR) spectral data for D and E.

Draw the structures of D and E and explain how the spectral data in Table 16.1 provides evidence for the structures.

Draw the structures of the products you would expect from the ozonolysis of the two compounds below.

This question is about carbonyl compounds.

Describe a chemical test to confirm the presence of a carbonyl group.

How could the product of this test be used to identify the carbonyl compound?

Your answer should not include spectroscopy.

Describe a chemical test that would identify whether a carbonyl compound is an aldehyde.

Your answer should include the reagent and observations.

A student is provided with two unknown carbonyl compounds, F and G.

The compounds are analysed and found to have identical percentage compositions by mass: C: 62.07%; H: 10.34%; O: 27.59%

The mass spectra of the two compounds are shown below.

Use the results to identify the structures of the two compounds.

Include relevant peaks present in the mass spectrum of each compound.

This question is about reactions of phenol.

Complete the mechanism below for Stage 1 and Stage 2.

Show curly arrows, the structure of the intermediate and the missing formulae on the dotted lines.

Two molecules of salicylic acid can react together in the presence of an acid catalyst to form compound B.

Compound B has three rings and a molecular formula of C₁₄H₈O₄.

Write the equation for this reaction showing the structures of organic compounds.

A student reacts phenol with nitric acid and sulfuric acid at 100 °C to form impure crystals of an organic compound, C. The student purifies the crystals by recrystallisation.

Describe how the student could recrystallise the impure crystals to obtain a pure sample of C.

The pure sample of C is analysed to give the following results.

Percentage composition by mass: C, 31.44%; H, 1.31%; N, 18.34%; O, 48.91%.

The mass spectrum of C shows a molecular ion peak at m / z = 229.0

The¹³C NMR spectrum of C is shown below.

The table shows directing effects for different groups in the electrophilic substitution of aromatic compounds.

Analyse all the information to suggest the structure for C.

Show all your reasoning.

compound C

21* Compounds D, E and F are isomers with the molecular formula C₅H₁₀O. One of the compounds is alicyclic.

A student carries out test-tube tests on the compounds. The observations are shown below.

¹³C NMR spectrum of D
Compound D has 3 peaks at / ppm: 24, 36, 73.

¹H NMR spectra of E and F The integration data has been omitted.

Compound E

Compound F

Analyse the observations and results to identify the structures of D, E and F.

Explain your reasoning.

An organic compound I is analysed, using a combination of techniques. The analytical data is shown below.

Elemental analysis by mass C, 56.69%; H, 7.09%; N, 11.02%; O, 25.20%

Mass spectrum Molecular ion peak at m / z = 127.0

IR spectrum

Proton NMR spectrum

Explain the use of two deuterated compounds in NMR spectroscopy.

* Determine the structure of compound I, showing all your reasoning.

21* Analysis of an unknown organic compound produced the following results.

Elemental analysis by mass C: 73.17%; H: 7.32%; O: 19.51%

Mass spectrum Molecular ion peak at m / z = 164.0

Infrared spectrum

The numbers by the peaks are the relative peak areas.

Use the results to suggest one possible structure for the unknown compound.

Show all your reasoning.

This question is about aromatic carboxylic acids and their derivatives.

The concentration of ester K in the cosmetic product is 9.13 × 10⁻² g dm⁻³.

Using the results, calculate the concentration, in mol dm⁻³, of ester M in the cosmetic product.

Give your answer to two significant figures.

concentration of ester M =........ mol dm⁻³

The relative molecular masses and boiling points of some fuels are shown in Table 22.1.

Write an equation for the incomplete combustion of heptane.

Explain the difference in the boiling points of the fuels in Table 22.1.

Fuel additives are often used to improve the combustion of a fuel.

Compound N is a fuel additive containing carbon, hydrogen and oxygen only.

Complete combustion of 1.71 g of compound N produces 2.97 g of CO₂ and 1.62 g of H₂O. The relative molecular mass of compound N is 76.0.

Calculate the molecular formula of N and suggest a possible structure for the compound.

compound N

Solketal has been investigated as a potential fuel additive.

Solketal is synthesised from propane-1,2,3-triol and a carbonyl compound.

Construct a balanced equation for this synthesis. Show structures for the organic compounds in your equation.

* A scientist is researching compounds that might be suitable as fuel additives. One of the compounds gives the analytical results below.

Elemental analysis by mass: C: 54.54%; H: 9.10%; O: 36.36%

Mass spectrum: Molecular ion peak at m / z = 132.0

¹H NMR spectrum in D₂O

The numbers by the peaks are the relative peak areas.

When the spectrum is run without D₂O, there are two additional peaks with the same relative peak areas at 11.0 ppm and 3.6 ppm.

Use the information provided to suggest a structure for the compound.

Show all your reasoning.

A chemist analyses a naturally occurring aromatic compound.

The percentage composition and mass spectrum of the compound are shown below.

Percentage composition by mass: C, 70.58%; H, 5.92%; O, 23.50%.

Mass spectrum

Determine the molecular formula of the compound.

Show your working.

Qualitative tests are carried out on the aromatic compound. The results are shown below.

Determine the functional groups in the compound. Explain your reasoning.

Functional groups........

Explanation........

The carbon-13 NMR spectrum of the compound is shown below.

Using the spectrum and the results from (a) and (b), determine the structure of the compound. Explain your reasoning.

Structure of compound