22.2. Mass spectrometry
A subsection of Chemistry, 9701, through 22. Analytical techniques
Listing 10 of 98 questions
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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An aldehyde, an alkane and a carboxylic acid, all of similar volatility, are mixed together. The mixture is then analysed in a gas chromatograph. The gas chromatogram produced is shown. absorption time / mins Z X Y The separation of the compounds depends on their relative solubilities in the stationary phase. The stationary phase is a liquid alcohol. Complete the table to suggest which compound in the mixture is responsible for each peak X, Y and Z. Explain your answer by reference to the intermolecular forces of the compounds. peak organic compound explanation X Y Z  A student calculates the areas underneath the three peaks in the chromatogram. peak X Y Z area / mm2 The area underneath each peak is proportional to the mass of the respective compound. Calculate the percentage by mass in the original mixture of the compound responsible for peakZ.  % of mixture responsible for peak Z = The mass spectrum of a halogenoalkane containing one chlorine atom or bromine atom will show an additional peak at M+2. State the isotopes of chlorine and bromine responsible for M+2 peaks. chlorine bromine  The mass spectrum of bromochloromethane, CH2BrCl, has a molecular ion peak, M, at an m / e value of 128. It also has M+2 and M+4 peaks. Suggest the identity of the molecular ions that give rise to these peaks. M peak M+2 peak M+4 peak  Halogenoalkanes can be formed from the reaction of an alkene with a hydrogen halide. Methylpropene reacts with hydrogen bromide to form 2-bromo-2-methylpropane. H2C CH3 CH3 C + HBr methylpropene 2-bromo-2-methylpropane H3C CH3 Br CH3 C Draw the mechanism of this reaction. Include all relevant curly arrows, dipoles and charges.  1-bromo-2-methylpropane is also formed in this reaction. Explain why 2-bromo-2-methylpropane will be the major product in this reaction. Explain what is meant by the term partition coefficient, Kpartition. The partition coefficient of organic compound H between dichloromethane and water is 4.75. ● 2.50 g of compoundH was dissolved in water and made up to 100 cm3 in a volumetric flask. ● 50 cm3 of this aqueous solution were shaken with 10 cm3 of dichloromethane. Calculate the mass of compoundH that was extracted into the dichloromethane.  mass of compound H extracted = g 
9701_w18_qp_41
THEORY
2018
Paper 4, Variant 1
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An aldehyde, an alkane and a carboxylic acid, all of similar volatility, are mixed together. The mixture is then analysed in a gas chromatograph. The gas chromatogram produced is shown. absorption time / mins Z X Y The separation of the compounds depends on their relative solubilities in the stationary phase. The stationary phase is a liquid alcohol. Complete the table to suggest which compound in the mixture is responsible for each peak X, Y and Z. Explain your answer by reference to the intermolecular forces of the compounds. peak organic compound explanation X Y Z  A student calculates the areas underneath the three peaks in the chromatogram. peak X Y Z area / mm2 The area underneath each peak is proportional to the mass of the respective compound. Calculate the percentage by mass in the original mixture of the compound responsible for peakZ.  % of mixture responsible for peak Z = The mass spectrum of a halogenoalkane containing one chlorine atom or bromine atom will show an additional peak at M+2. State the isotopes of chlorine and bromine responsible for M+2 peaks. chlorine bromine  The mass spectrum of bromochloromethane, CH2BrCl, has a molecular ion peak, M, at an m / e value of 128. It also has M+2 and M+4 peaks. Suggest the identity of the molecular ions that give rise to these peaks. M peak M+2 peak M+4 peak  Halogenoalkanes can be formed from the reaction of an alkene with a hydrogen halide. Methylpropene reacts with hydrogen bromide to form 2-bromo-2-methylpropane. H2C CH3 CH3 C + HBr methylpropene 2-bromo-2-methylpropane H3C CH3 Br CH3 C Draw the mechanism of this reaction. Include all relevant curly arrows, dipoles and charges.  1-bromo-2-methylpropane is also formed in this reaction. Explain why 2-bromo-2-methylpropane will be the major product in this reaction. Explain what is meant by the term partition coefficient, Kpartition. The partition coefficient of organic compound H between dichloromethane and water is 4.75. ● 2.50 g of compoundH was dissolved in water and made up to 100 cm3 in a volumetric flask. ● 50 cm3 of this aqueous solution were shaken with 10 cm3 of dichloromethane. Calculate the mass of compoundH that was extracted into the dichloromethane.  mass of compound H extracted = g 
9701_w18_qp_43
THEORY
2018
Paper 4, Variant 3
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The structure of butamben is shown. H2N O O butamben Butamben can act as a base. Complete the equation for a reaction in which butamben acts as a base. H2N O O +  Predict whether butamben is a stronger or weaker base than ammonia. Give a reason for your answer. Complete the reaction scheme below to show the structural formulae of the products formed when butamben is treated separately with the stated reagent. H2N O O Br2HNO2+ HCl 5 °C NaOHunder reflux  The proton NMR spectrum of butamben in CDCl 3 contains one or more peaks that show a triplet splitting pattern. State the number of peaks in the spectrum that show a triplet splitting pattern. On the diagram of butamben below, circle the protons responsible for the peak or peaks you identified in . H N H C C O O H H H H H H H H H C C H H H C H  Describe and explain how the proton NMR spectrum of butamben in D2O would differ from the proton NMR spectrum of butamben in CDCl 3. The mass spectrum of butamben includes peaks at m/e 92 and 57. Identify the fragments responsible for these peaks. m/e 92 = m/e 57 =  
9701_w19_qp_41
THEORY
2019
Paper 4, Variant 1
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The structure of butamben is shown. H2N O O butamben Butamben can act as a base. Complete the equation for a reaction in which butamben acts as a base. H2N O O +  Predict whether butamben is a stronger or weaker base than ammonia. Give a reason for your answer. Complete the reaction scheme below to show the structural formulae of the products formed when butamben is treated separately with the stated reagent. H2N O O Br2HNO2+ HCl 5 °C NaOHunder reflux  The proton NMR spectrum of butamben in CDCl 3 contains one or more peaks that show a triplet splitting pattern. State the number of peaks in the spectrum that show a triplet splitting pattern. On the diagram of butamben below, circle the protons responsible for the peak or peaks you identified in . H N H C C O O H H H H H H H H H C C H H H C H  Describe and explain how the proton NMR spectrum of butamben in D2O would differ from the proton NMR spectrum of butamben in CDCl 3. The mass spectrum of butamben includes peaks at m/e 92 and 57. Identify the fragments responsible for these peaks. m/e 92 = m/e 57 =  
9701_w19_qp_43
THEORY
2019
Paper 4, Variant 3
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The proton NMR spectrum of compoundE in the solvent CDCl 3 is shown. The molecular formula of compoundE is C9H10O2. δ / ppm Explain why CDCl 3 is used as a solvent instead of CHCl 3. Explain why TMS is added to give the small peak at chemical shift δ = 0. CompoundE is hydrolysed by hot NaOH, giving two organic products only. One of these products is ethanol. Name the functional group in compoundE that is hydrolysed by hot NaOH. Describe and explain the splitting patterns of the peaks at δ = 1.4 and δ = 4.3. splitting pattern at δ = 1.4 reason for splitting pattern at δ = 1.4 splitting pattern at δ = 4.3 reason for splitting pattern at δ = 4.3  Each molecule of compoundE contains five protons which give rise to the peaks between δ=7.0 and δ=8.5. Identify the functional group in compoundE which contains these protons. Give the structural formula of compoundE.  The mass spectrum of compoundE includes fragment ions with m/e values of 29 and 77. Give the formulae of these fragment ions. fragment ion with m/e = 29 fragment ion with m/e = 77  
9701_w20_qp_41
THEORY
2020
Paper 4, Variant 1
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Questions Discovered
98