22.2. Mass spectrometry
A subsection of Chemistry, 9701, through 22. Analytical techniques
Listing 10 of 98 questions
This question is about compound T, CxHyOz. Part of the mass spectrum of T is shown. The peak heights of the M and M+1 peaks are 33.9 and 3.4 respectively. relative intensity m / e Calculate x, the number of carbon atoms present in T. x = Deduce the molecular formula of T. The mass spectrum has a peak at m / e = 119. Identify the fragment lost from T to produce this peak. The infra-red spectrum of T is shown. transmittance wavenumber / cm–1 V W Identify the type of bond responsible for each of the peaks V and W. Use the Data Booklet to help you. V W The proton NMR spectrum of T in CDCl 3 is shown. δ / ppm 3H 3H 4H Complete the table for the proton NMR spectrum of T. Use the Data Booklet to help you. δ / ppm type of proton 3.9 7.2–7.9 The peak at δ=2.4 ppm is due to a proton attached to a saturated carbon atom. State the two possible types of proton. 1. 2. Adding D2O to T does not change its proton NMR spectrum. What does this tell you about the functional groups present in T? Use the information to draw two possible structures of T which are functional group isomers of each other.
9701_m17_qp_42
THEORY
2017
Paper 4, Variant 2
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Two molecules of compoundF react together under suitable conditions to form compoundG. Some information about compounds F and G is given. ● ● The mass spectrum of F has a peak due to the molecular ion at m / e=106, and a peak at m / e=107 with an abundance 8% of the 106 peak. ● ● The mass spectrum of G has a peak due to the molecular ion at m / e=212, and major peaks at m / e=91 and m / e=105. ● ● Both F and G contain oxygen and are neutral compounds which are insoluble in water. ● ● The 1H NMR spectrum of F includes a singlet peak at δ=10.0 due to one proton. ● ● The 1H NMR spectrum of G includes a singlet peak at δ=5.1 due to two protons. ● ● When G is heated with dilute sulfuric acid, benzoic acid, C6H5CO2H, and phenylmethanol, C6H5CH2OH, are produced. Use this information to answer – . Explain how the mass spectrum of F shows that a molecule of F contains seven carbon atoms. Show your working.  Suggest the molecular formula of the fragment of G at m / e=91. Suggest the molecular formulae of F and G. F G  Suggest structures for compounds F and G. F G  On the structures you have drawn in , circle the protons responsible for the 1HNMR peaks at δ=10.0 in F and δ=5.1 in G. State the type of reaction that G undergoes when heated with dilute sulfuricacid. Describe and explain the relative acidities of benzoicacid, phenylmethanol and 4-methylphenol. CO2H benzoic acid CH2OH H3C phenylmethanol OH 4-methylphenol The ester 4-methylphenyl benzoate is used in the manufacture of perfumes. O O 4-methylphenyl benzoate H3C Suggest a two-step route for the synthesis of 4-methylphenyl benzoate from 4-methylphenol and benzoicacid. Include reagents and conditions for each step, and the structure of the intermediate compound.  
9701_m18_qp_42
THEORY
2018
Paper 4, Variant 2
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The names of many drugs used in medicine often include parts of the names of the functional groups their molecules contain. Suggest two functional groups present in a molecule of the drug named chloramphenicol.  The drug named ketamine readily reacts with protons as shown. ketamine + H+ [ketamine-H]+ State the role of ketamine in this reaction. Ketamine gives an orange precipitate with 2,4-dinitrophenylhydrazine (2,4-DNPH). Suggest the functional group in the ketamine molecule responsible for this observation. The mass spectrum of ketamine is determined. Two peaks close to the molecular ion peak, M, are observed with the relative abundances shown in the table. peak m / e relative abundance M 100.0 M+1 14.3 M+2 33.3 Use the numbers in the table to show that there are 13 carbon atoms in a ketamine molecule.  In addition to carbon and hydrogen atoms, each molecule of ketamine contains one atom of each of three different elements. These are called heteroatoms. One of these heteroatoms is a halogen. Use the figures in the table to suggest the identity of this halogen. Explain your answer. Another peak in the mass spectrum of ketamine has an m / e value of 240. Predict the relative abundance of this peak.  relative abundance = Use the information in to complete the molecular formula of ketamine by working out the identities of the three different heteroatoms and the number of hydrogen atoms present. C13H  Neramexane is another drug. NH2 neramexane Suggest the number of peaks in the carbon-13 NMR spectrum of neramexane. The proton (1H) NMR spectrum of neramexane in CDCl 3 shows five peaks with the following chemical shifts (δ). δ / ppm number of protons responsible splitting pattern (singlet, doublet, triplet, quartet or multiplet) 0.9 singlet 1.2 1.4 1.7 2.2 broad singlet Complete the table. Use the Data Booklet and the table in to complete the assignment of the correct δvalues to each of the circled hydrogen atoms on the structure of neramexane. NH2 CH3 CH3 CH3 H3C H3C CH2 H2C CH2 C C C δ = 1.2  One of the peaks in the proton (1H) NMR spectrum disappears when the sample is shaken with D2O. Identify the peak and explain why it disappears. 
9701_m19_qp_42
THEORY
2019
Paper 4, Variant 2
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A range of modern analytical techniques has made the identification of molecules, and atoms in compounds, much more rapid than traditional laboratory analysis. One instrumental technique is NMR spectroscopy, which uses the fact that under certain conditions protons can exist in two different energy states. Explain how these different energy states arise. When methanol, CH3OH, is examined using NMR spectroscopy, it absorbs at two different frequencies. Explain why, and predict the relative areas of the two peaks. The NMR spectrum below is that of one of three possible isomers of molecular formula C3H6O2. chemical shift, δ / ppm A B The compound could be propanoic acid, methyl ethanoate or ethyl methanoate. In the boxes provided, draw the structures of the three compounds. propanoic acid methyl ethanoate ethyl methanoate Explain which compound produced the spectrum shown, indicating which protons are responsible for each of the peaks A and B. The NMR spectrum of another of the compounds has a peak at δ11.0. State which compound this would be, and identify the protonresponsible for this peak. compound proton X-ray crystallography is a technique used to identify the relative positions of atoms in a crystal of a compound. What further information about organic macromolecules can be deduced by the use of X-ray crystallography? Which atoms cannot be located by X-ray crystallography?
9701_s10_qp_41
THEORY
2010
Paper 4, Variant 1
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