22. Analytical techniques
A section of Chemistry, 9701
Listing 10 of 112 questions
NMR spectroscopy and X-ray crystallography are two techniques that use electromagnetic radiation to look at the structures of large molecules. For each technique state the sub-atomic particle involved, and explain how this particle interacts with the radiation. NMR X-ray The two NMR spectra 1 and 2 were obtained before and after an alcohol, Y, was oxidised to give compound Z. The numbers of hydrogen atoms responsible for each peak have not been shown. All the peaks have been shown. δ / ppm δ / ppm State which spectrum, 1 or 2, was produced by the alcohol, giving a reason for your answer. spectrum reason The mass spectrum of Y showed an M : M + 1 peak ratio of 17.6:0.6. Use this and other information in the question to suggest the identities of both Y and Z. Draw a displayed formula for Y in the box provided Y is Explain why the NMR spectrum of Z only shows one peak.
9701_w10_qp_41
THEORY
2010
Paper 4, Variant 1
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NMR spectroscopy and X-ray crystallography are two techniques that use electromagnetic radiation to look at the structures of large molecules. For each technique state the sub-atomic particle involved, and explain how this particle interacts with the radiation. NMR X-ray The two NMR spectra 1 and 2 were obtained before and after an alcohol, Y, was oxidised to give compound Z. The numbers of hydrogen atoms responsible for each peak have not been shown. All the peaks have been shown. δ / ppm δ / ppm State which spectrum, 1 or 2, was produced by the alcohol, giving a reason for your answer. spectrum reason The mass spectrum of Y showed an M : M + 1 peak ratio of 17.6:0.6. Use this and other information in the question to suggest the identities of both Y and Z. Draw a displayed formula for Y in the box provided Y is Explain why the NMR spectrum of Z only shows one peak.
9701_w10_qp_42
THEORY
2010
Paper 4, Variant 2
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Although the chemical reactions of compounds remain important pointers to their functional groups, instrumental techniques such as mass spectrometry and NMR spectroscopy are increasingly used to determine molecular structures. Compound J was analysed using these two techniques with the following results. The mass spectrum showed that ● the M peak was at m/e 86, ● the ratio of heights of the M and M+1 peaks was 23.5 : 1.3. The NMR spectrum is shown below. δ / ppm Use the data to determine the number of carbon and hydrogen atoms present in J, showing your working. Use the information given above and your answer to to identify the other element present in J. Determine the structure of J, explaining how you reach your conclusion. structure of J explanation Chromatography is another important analytical technique used in chemistry. Paper, thin-layer and gas-liquid chromatography rely on different physical methods to separate the components in a mixture. Complete the table indicating the appropriate method on which the technique is based. technique physical method paper chromatography thin-layer chromatography gas-liquid chromatography In paper chromatography, better separation may be achieved by running the chroma- togram in one solvent, then turning the paper at right angles and running it in a second solvent. The chromatogram below was produced in this way. solvent 1 solvent 2 sample applied here How many spots were visible before solvent 2 was used? Ring the spot that did not move in solvent 2. How many spots travelled further in solvent 2 than they did in solvent 1?
9701_w12_qp_43
THEORY
2012
Paper 4, Variant 3
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Instrumental analysis plays an increasingly important role in modern chemistry. Two important techniques are NMR spectroscopy and X-ray crystallography. Both techniques use part of the electromagnetic spectrum. Which technique uses radiation with the longer wavelength, and in which part of the spectrum is it found? NMR spectroscopy provides detailed information about protons, but X-ray crystallography is unable to detect them. Explain these facts. The protein found in hair contains the amino acid cysteine, C3H7SNO2. Crystalline cysteine was examined using X-ray crystallography. State which atom produced the strongest refl ection, explaining your answer. Compound P is an alcohol that can be converted into compound Q in the following reaction sequence. P → CxH6O → Q Spectral analyses of P and Q were carried out. The mass spectrum of P shows an M : M+1 peak ratio of 4.5 : 0.15. Calculate the number of carbon atoms in P. The NMR spectra of P and Q are shown below. δ / ppm δ / ppm P Q In the spectrum of P, clearly label the peak due to the –OH group with an X. State how many different proton environments are present in compound Q. What evidence is there in these spectra that P is a primary rather than a secondary alcohol? Draw a structure for Q.
9701_w13_qp_43
THEORY
2013
Paper 4, Variant 3
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T is a saturated alcohol. It was analysed by mass spectroscopy and NMR spectroscopy. In the mass spectrum, the molecular ion peak, M, was at an m/e value of 74 and the ratio of the heights of the M and M+1 peaks was 20.4 : 0.9. Use the ratio of the heights of the M and M+1 peaks to calculate the number of carbon atoms in a molecule of T. What is the molecular formula of T? molecular formula = The NMR spectrum of T given below shows four absorptions. The absorption at 1.8 ppm is a multiplet and that at 2.5 ppm is a singlet. δ / ppm Use this information and your answer to to deduce the structure of T. T Describe and explain which type of proton is responsible for each of the absorptions. The absorption at 1.8 ppm is a multiplet and that at 2.5 is a singlet. State and explain the splitting patterns of the other absorptions, at 0.9 and 3.4 ppm. Describe and explain how the NMR spectrum of T dissolved in D2O would differ from the one shown.
9701_w14_qp_41
THEORY
2014
Paper 4, Variant 1
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T is a saturated alcohol. It was analysed by mass spectroscopy and NMR spectroscopy. In the mass spectrum, the molecular ion peak, M, was at an m/e value of 74 and the ratio of the heights of the M and M+1 peaks was 20.4 : 0.9. Use the ratio of the heights of the M and M+1 peaks to calculate the number of carbon atoms in a molecule of T. What is the molecular formula of T? molecular formula = The NMR spectrum of T given below shows four absorptions. The absorption at 1.8 ppm is a multiplet and that at 2.5 ppm is a singlet. δ / ppm Use this information and your answer to to deduce the structure of T. T Describe and explain which type of proton is responsible for each of the absorptions. The absorption at 1.8 ppm is a multiplet and that at 2.5 is a singlet. State and explain the splitting patterns of the other absorptions, at 0.9 and 3.4 ppm. Describe and explain how the NMR spectrum of T dissolved in D2O would differ from the one shown.
9701_w14_qp_42
THEORY
2014
Paper 4, Variant 2
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A mixture of volatile organic compounds X, Y and Z can be separated in a gas chromatograph. Their identities can be confirmed by measuring their different retention times and comparing to known values. A gas chromatogram is shown. absorption X Y Z time / mins Suggest what is meant by the term retention time. Give an example of a carrier gas used in gas chromatography. Z spends the longest time in the chromatography column. Suggest why this might be the case. Explain a possible limitation of gas / liquid chromatography in separating two esters such as ethyl methanoate, HCO2CH2CH3, and methyl ethanoate, CH3CO2CH3. A student works out the areas underneath the three peaks in the chromatogram. peak X Y Z area / mm2 Assuming the areas underneath the peaks are proportional to the masses of the respective components, what percentage of the original mixture was made up of the organic compound, X? % of X = The NMR spectrum of Y given below shows four absorptions. absorption δ / ppm What compound is responsible for the absorption at δ = 0? Compound Y is an ester with the molecular formula C4H8O2. Complete the table for the NMR spectrum of Y. The actual chemical shifts for three absorptions in Y and the splitting pattern for the resonance at δ = 3.7 ppm have been given for you. Use of the Data Booklet may be helpful. chemical shift δ / ppm type of protonnumber of protons splitting pattern 1.0 2.3 3.7 singlet Use your conclusions to suggest a structure for the ester Y.
9701_w15_qp_43
THEORY
2015
Paper 4, Variant 3
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Compound F contains the elements carbon, hydrogen and oxygen only. All carbon-carbon bonds in F are single bonds. The structure of F was analysed by mass spectrometry and infra-red and NMRspectroscopy. The mass spectrum shows that the m / e value for the M peak is 90. The ratio of the heights of the M and M+1 peaks is 22.1 : 0.7. Use the ratio of the heights of the M and M+1 peaks to calculate the number of carbon atoms in a molecule of F. number of carbon atoms = Suggest the molecular formula of F. molecular formula = C H O The infra-red spectrum of F was obtained. Use the Data Booklet and your knowledge of infra-red spectroscopy to identify the type of bond and the functional group responsible for these three absorptions. absorption / cm–1 appearance of the peak type of bond functional group broad and strong very broad and strong strong F was dissolved in deuterated trichloromethane, CDCl 3, and the proton NMR spectrum of this solution obtained. δ / ppm Use the Data Booklet and your answer to to complete Table1 for the proton NMR spectrum of F. The actual chemical shifts for the four absorptions in F have been added for you. Table 1 δ / ppm type of proton relative peak area 1.4 3.9 4.7 12.9 Describe and explain the splitting pattern for the absorption at δ = 1.4. F was dissolved in D2O and the proton NMR spectrum of this new solution obtained. Two of the absorptions in Table1 were not present in this spectrum. Which absorptions were not present?  and Suggest the structure of F. Molecules of cycloheptadiene, C7H10, consist of a seven-membered ring with two carbon-carbon double bonds. Complete the skeletal formulae of two isomers of cycloheptadiene. P Q The isomers P and Q were analysed using carbon-13 NMR spectroscopy. Predict the number of peaks that will be seen in the carbon-13 NMR spectra of P and Q. isomer number of peaks P Q
9701_w16_qp_41
THEORY
2016
Paper 4, Variant 1
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Compound F contains the elements carbon, hydrogen and oxygen only. All carbon-carbon bonds in F are single bonds. The structure of F was analysed by mass spectrometry and infra-red and NMRspectroscopy. The mass spectrum shows that the m / e value for the M peak is 90. The ratio of the heights of the M and M+1 peaks is 22.1 : 0.7. Use the ratio of the heights of the M and M+1 peaks to calculate the number of carbon atoms in a molecule of F. number of carbon atoms = Suggest the molecular formula of F. molecular formula = C H O The infra-red spectrum of F was obtained. Use the Data Booklet and your knowledge of infra-red spectroscopy to identify the type of bond and the functional group responsible for these three absorptions. absorption / cm–1 appearance of the peak type of bond functional group broad and strong very broad and strong strong F was dissolved in deuterated trichloromethane, CDCl 3, and the proton NMR spectrum of this solution obtained. δ / ppm Use the Data Booklet and your answer to to complete Table1 for the proton NMR spectrum of F. The actual chemical shifts for the four absorptions in F have been added for you. Table 1 δ / ppm type of proton relative peak area 1.4 3.9 4.7 12.9 Describe and explain the splitting pattern for the absorption at δ = 1.4. F was dissolved in D2O and the proton NMR spectrum of this new solution obtained. Two of the absorptions in Table1 were not present in this spectrum. Which absorptions were not present?  and Suggest the structure of F. Molecules of cycloheptadiene, C7H10, consist of a seven-membered ring with two carbon-carbon double bonds. Complete the skeletal formulae of two isomers of cycloheptadiene. P Q The isomers P and Q were analysed using carbon-13 NMR spectroscopy. Predict the number of peaks that will be seen in the carbon-13 NMR spectra of P and Q. isomer number of peaks P Q
9701_w16_qp_43
THEORY
2016
Paper 4, Variant 3
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Questions Discovered
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