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22.2. Mass spectrometry
A subsection of Chemistry, 9701, through 22. Analytical techniques
Listing 10 of 98 questions
But-2-ene reacts with KMnO4 to form organic product, Y. Y does not react with Na2CO3. A gas is produced when an excess of Na is added to Y. Describe the conditions for the KMnO4 used in the reaction to form Y from but-2-ene. 24.0 cm3 of gas is produced when an excess of Na is added to 0.001 mol of Y, when measured under room conditions. Assume that 1 mol of gas occupies 24.0 dm3 under room conditions. Deduce a possible structure of Y. Explain your answer.  Z contains three types of atom: carbon, hydrogen and a halogen. The mass spectrum of Z is recorded. Fig.5.1 shows a section of the mass spectrum at m/e greater than 63. The fragment at m/e = 64 is the molecular ion peak. 2.2 33.3 relative abundance m/e Deduce the number of carbon atoms present in a molecule of Z using Fig.5.1. Show your working. Deduce which halogen is present in Z using Fig.5.1. Explain your answer. There are also peaks at m/e = 29 and m/e = 49. Suggest the formulae of these fragments. Deduce the name of Z. m/e = 29 m/e = 49 name of Z  
9701_s22_qp_23
THEORY
2022
Paper 2, Variant 3
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State the uses of TMS and D2O in NMR spectroscopy. TMS D2O  The three isomeric ketones with molecular formula C5H10O are: ● pentan-2-one ● pentan-3-one ● 3-methylbutanone. Complete Table 7.1 to show the number of peaks observed in the proton (1H) NMR spectrum and in the carbon-13 NMR spectrum for each compound listed. Table 7.1 ketone number of peaks observed in the proton (1H) NMR spectrum number of peaks observed in the carbon-13 NMR spectrum pentan-2-one pentan-3-one 3-methylbutanone  State all the ketones with molecular formula C5H10O that have: a doublet in their proton (1H) NMR spectrum a singlet in their proton (1H) NMR spectrum.  Cortisone, C21H28O5, is a naturally occurring chemical that contains chiral carbon atoms. CH3 O O O CH3 OH OH cortisone Deduce the number of chiral carbon atoms in one molecule of cortisone. Cortisone is reacted with an excess of NaBH4. State the molecular formula of the organic compound formed. Cortisone is an optically active molecule. Explain what is meant by optically active. 
9701_s22_qp_42
THEORY
2022
Paper 4, Variant 2
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Explain with reference to energy states how 1H NMR can supply information about the structure of molecules. Nuclear magnetic resonance is used in magnetic resonance imaging scanners. These scanners are increasingly used in hospitals to detect tumours. Suggest why magnetic resonance techniques are better than X-rays. Examiner’s Use The NMR spectrum shown below was obtained from a simple organic molecule, G, CxHyO2. When a sample of G was placed in a mass spectrometer, the ratio of the M : M+1 peaks for the molecule was 14.5 : 0.66. absorbance chemical shift,  Calculate how many carbon atoms there are in the molecule. Use the NMR spectrum and the Data Booklet to work out the structure of G.
9701_w07_qp_4
THEORY
2007
Paper 4, Variant 0
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Use The technology of DNA fingerprinting has enormously advanced scientific identification techniques in medicine, crime detection and archaeology in recent years. In order to prepare a DNA sample for analysis, the DNA is treated with restriction enzymes. What do restriction enzymes do? What is the next stage in DNA analysis, after the treatment with restriction enzymes? How are the DNA fragments made visible? NMR and X-ray crystallography have made significant contributions to our knowledge of the structure of proteins and, in the pharmaceutical industry, how drugs react with target proteins. Suggest an advantage of each technique in helping to determine protein structure. MRI scanning is a medical technique based on NMR spectroscopy. It is particularly useful for looking for tumours in healthy tissue. Suggest how this technique can distinguish tumour tissue from healthy tissue. Examiner’s Use A saturated molecule of formula CxHyNO was subjected to analysis by mass spectrometry and NMR spectroscopy. In the mass spectrum of the compound, the M peak was at m/e 73 and the ratio of the heights of the M:M+1 peak was 48 : 1.7. Using the data from the mass spectrum, determine the values of x and y in the formula of the compound. Use the data from together with the NMR spectrum below to deduce a structure for the compound, explaining how you arrive at your answer. chemical shift,  / ppm
9701_w08_qp_4
THEORY
2008
Paper 4, Variant 0
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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_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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10 Instrumental methods of analysis have become increasingly important in recent years. The use of chromatography to separate substances, and NMR spectroscopy to identify them, has become routine in many laboratories. Chromatography relies on either partition or adsorption to help separate substances. Briefly explain how each method brings about separation. partition adsorption The table shows three different techniques of chromatography. Identify which separation method, partition or adsorption, applies to each. technique separation method paper chromatography thin-layer chromatography gas/liquid chromatography The diagram represents the output from gas/liquid chromatography carried out on a mixture. time injection detector response air peak solvent peak X Y Determine the percentage of each of the two components X and Y in the mixture. NMR spectroscopy is a very important analytical technique for use with organic compounds. Why is NMR spectroscopy particularly useful for organic compounds? Two molecules, propanal and propanone, have the same molecular formula, C3H6O. Draw the displayed formula of each compound and explain briefly how NMR spectroscopy can distinguish between the two structures.
9701_w10_qp_43
THEORY
2010
Paper 4, Variant 3
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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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Questions Discovered
98