22.2. Mass spectrometry
A subsection of Chemistry, 9701, through 22. Analytical techniques
Listing 10 of 98 questions
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_43
THEORY
2020
Paper 4, Variant 3
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CompoundT is made by a three-stage synthesis. In stage1, phenylethanoicacid reacts with a suitable reagent to form compoundR. O OH O Cl phenylethanoic acid R stage 1 Suggest a suitable reagent for stage1. In stage 2, compoundR reacts with ethylamine to form compoundS. + C2H5NH2 O Cl R O S stage 2 N H Name the functional group formed in stage2. Identify the other product formed in stage2. In stage3, compoundS reacts with a suitable reagent to form compoundT. O S stage 3 N H T N H State the formula of a suitable reagent for stage3. Name the type of reaction that occurs in stage3. The relative abundance of the molecular ion peak in the mass spectrum of ethylamine is 62. Calculate the relative abundance of the M+1 peak in the mass spectrum of ethylamine.  relative abundance = The mass spectrum of compoundT contains several fragments. The m/e values of two of these fragments are 29 and 91. Draw the structures of the ions responsible for these peaks. m/e structure of ion  The proton (1H) NMR spectrum of compoundT shows hydrogen atoms in different environments. Six of these environments are shown on the structure using letters a, b, c, d, e and f. N H a b c e d f Use the letters a, b, c, d, e and f to answer the questions that follow. The questions relate to the proton (1H) NMR spectrum of T. Proton d does not cause splitting of the peaks for protons c or e under the conditions used. Each answer may be one, or more than one, of the letters a, b, c, d, e and f. Identify the proton or protons with a chemical shift (δ) in the range 6.0 to 9.0.  Identify the proton or protons whose peak will disappear if D2O is added.  Identify the proton or protons whose peak is a triplet.  Identify the proton or protons with the lowest chemical shift (δ).  
9701_w21_qp_41
THEORY
2021
Paper 4, Variant 1
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Alanine, H2NCH(CH3)CO2H, and glutamic acid, H2NCH(CH2CH2CO2H)CO2H, are two naturally occurring amino acids. H2NCH(CH3)CO2H exists as two optical isomers. Draw three-dimensional structures of these two optical isomers.  The proton (1H) NMR spectrum of either alanine in D2O or glutamic acid in D2O is shown. / ppm State whether this is the spectrum of alanine in D2O or the spectrum of glutamicacid in D2O. Explain your answer by reference to the number of peaks and splitting patterns. The mass spectrum of glutamicacid, H2NCH(CH2CH2CO2H)CO2H, is obtained. State the m/e value of the molecular ion peak in this spectrum. The spectrum has peaks with m/e values of 88 and 131. Draw the structures of the ions responsible for these peaks. m/e structure of ion  At pH 11 alanine exists as H2NCH(CH3)CO2 – ions and glutamic acid exists as H2NCH(CH2CH2CO2 –)CO2 – ions. A mixture of alanine and glutamicacid at pH 11 is subjected to electrophoresis. State how the mixture can be maintained at pH11 during electrophoresis. Draw a fully labelled diagram for the apparatus that would be used to carry out this electrophoresis. Your diagram should include the position of the mixture of alanine and glutamic acid at the start of the electrophoresis experiment. Identify the electrode that each amino acid travels towards during electrophoresis at pH11. alanine glutamic acid  In a particular electrophoresis experiment at pH 11, the glutamic acid travels 3.4 cm. Alanine travels a shorter distance. Explain the factors that account for the difference in the distances travelled. 
9701_w21_qp_42
THEORY
2021
Paper 4, Variant 2
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CompoundT is made by a three-stage synthesis. In stage1, phenylethanoicacid reacts with a suitable reagent to form compoundR. O OH O Cl phenylethanoic acid R stage 1 Suggest a suitable reagent for stage1. In stage 2, compoundR reacts with ethylamine to form compoundS. + C2H5NH2 O Cl R O S stage 2 N H Name the functional group formed in stage2. Identify the other product formed in stage2. In stage3, compoundS reacts with a suitable reagent to form compoundT. O S stage 3 N H T N H State the formula of a suitable reagent for stage3. Name the type of reaction that occurs in stage3. The relative abundance of the molecular ion peak in the mass spectrum of ethylamine is 62. Calculate the relative abundance of the M+1 peak in the mass spectrum of ethylamine.  relative abundance = The mass spectrum of compoundT contains several fragments. The m/e values of two of these fragments are 29 and 91. Draw the structures of the ions responsible for these peaks. m/e structure of ion  The proton (1H) NMR spectrum of compoundT shows hydrogen atoms in different environments. Six of these environments are shown on the structure using letters a, b, c, d, e and f. N H a b c e d f Use the letters a, b, c, d, e and f to answer the questions that follow. The questions relate to the proton (1H) NMR spectrum of T. Proton d does not cause splitting of the peaks for protons c or e under the conditions used. Each answer may be one, or more than one, of the letters a, b, c, d, e and f. Identify the proton or protons with a chemical shift (δ) in the range 6.0 to 9.0.  Identify the proton or protons whose peak will disappear if D2O is added.  Identify the proton or protons whose peak is a triplet.  Identify the proton or protons with the lowest chemical shift (δ).  
9701_w21_qp_43
THEORY
2021
Paper 4, Variant 3
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Gas-liquid chromatography involves a stationary phase and a mobile phase. Name, or describe in detail, a suitable substance that could be used for each phase. stationary mobile  A mixture of three organic compounds is separated by gas-liquid chromatography. The chromatogram obtained is shown in Fig.9.1. The amount of each substance is proportional to the area under its peak. retention time recorder response A C B Explain the meaning of retention time. Calculate the percentage of B in the mixture. Show your working.  percentage of B = % Complete Table9.1 to give the number of peaks in the carbon-13 NMR spectrum of each of the five isomers of C5H10O2 that has an ester group. Table 9.1 structural formula number of peaks CH3CH2CH2CO2CH3 CH3CH2CO2CH2CH3 CH3CO2CH2CH2CH3 (CH3)2CHCO2CH3 CH3CO2CH(CH3)2  State the number of peaks that would be seen in the proton (1H) NMR spectrum of methylbutanoate, CH3CH2CH2CO2CH3. Name all the splitting patterns seen in this spectrum. number of peaks splitting patterns  D and E are both esters with the molecular formula C5H10O2. Their proton (1H) NMR spectra are shown in Fig.9.2 and Fig.9.3. chemical shift, D chemical shift, E Table 9.2 environment of proton example typical chemical shift range, δ / ppm alkane –CH3, –CH2–, >CH– 0.9–1.7 alkyl next to C=O CH3–C=O, –CH2–C=O, >CH–C=O 2.2–3.0 alkyl next to aromatic ring CH3–Ar, –CH2–Ar, >CH–Ar 2.3–3.0 alkyl next to electronegative atom CH3–O, –CH2–O, –CH2–Cl 3.2–4.0 attached to alkene =CHR 4.5–6.0 Deduce the structures of the two esters D and E and draw their displayed formulae in the boxes below. D C5H10O2 E C5H10O2  The spectrum of D includes a quartet at δ4.1. Identify the protons responsible for this quartet on your structure in by labelling these protons with the letter F. Explain why this peak is split into a quartet.  The spectrum of E has a doublet at δ1.1. Identify the protons responsible for this doublet on your structure in by labelling these protons with the letter G. Explain why this peak has a chemical shift of 1.1.  
9701_w22_qp_41
THEORY
2022
Paper 4, Variant 1
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When answering this question it should be assumed that together all the hydrogen atoms in a benzene ring result in a single unsplit peak at δ = 7.2 in a proton (1H) NMR spectrum. The structures of five isomeric ketones, P, Q, R, S and T are given. P C6H5COCH(CH3)2 S C6H5CH2CH2COCH3 Q C6H5COCH2CH2CH3 T C6H5CH(CH3)COCH3 R C6H5CH2COCH2CH3 Identify all the chiral carbon atoms on the structures above. Label each chiral carbon atom with an asterisk (*). The proton (1H) NMR spectrum of one of the five isomers, P, Q, R, S or T, is shown in Fig.8.1. / ppm Identify which of the compounds P, Q, R, S or T gives this spectrum. Draw the displayed formula of the compound you have identified. Identify the protons responsible for the peaks at δ = 3.7, δ = 2.5 and δ = 1.0 on the structure you have drawn.  Name the splitting pattern of the peak at δ = 3.7. Explain why it has this splitting pattern. Choose from the letters P, Q, R, S and T to identify: the two compounds that each have a doublet peak in the proton (1H) NMR spectrum the compound with only three peaks in its proton (1H) NMR spectrum. Suggest a suitable solvent that should be used for obtaining the spectrum shown in Fig.8.1. The proton (1H) NMR spectrum of compoundT is compared in the presence of D2O and in the absence of D2O. Describe any difference between the two spectra. Explain your answer. Complete Table8.1 below to give the number of peaks in the carbon-13 NMR spectrum of each compound. Table 8.1 compound number of peaks compound number of peaks  
9701_w22_qp_42
THEORY
2022
Paper 4, Variant 2
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Gas-liquid chromatography involves a stationary phase and a mobile phase. Name, or describe in detail, a suitable substance that could be used for each phase. stationary mobile  A mixture of three organic compounds is separated by gas-liquid chromatography. The chromatogram obtained is shown in Fig.9.1. The amount of each substance is proportional to the area under its peak. retention time recorder response A C B Explain the meaning of retention time. Calculate the percentage of B in the mixture. Show your working.  percentage of B = % Complete Table9.1 to give the number of peaks in the carbon-13 NMR spectrum of each of the five isomers of C5H10O2 that has an ester group. Table 9.1 structural formula number of peaks CH3CH2CH2CO2CH3 CH3CH2CO2CH2CH3 CH3CO2CH2CH2CH3 (CH3)2CHCO2CH3 CH3CO2CH(CH3)2  State the number of peaks that would be seen in the proton (1H) NMR spectrum of methylbutanoate, CH3CH2CH2CO2CH3. Name all the splitting patterns seen in this spectrum. number of peaks splitting patterns  D and E are both esters with the molecular formula C5H10O2. Their proton (1H) NMR spectra are shown in Fig.9.2 and Fig.9.3. chemical shift, D chemical shift, E Table 9.2 environment of proton example typical chemical shift range, δ / ppm alkane –CH3, –CH2–, >CH– 0.9–1.7 alkyl next to C=O CH3–C=O, –CH2–C=O, >CH–C=O 2.2–3.0 alkyl next to aromatic ring CH3–Ar, –CH2–Ar, >CH–Ar 2.3–3.0 alkyl next to electronegative atom CH3–O, –CH2–O, –CH2–Cl 3.2–4.0 attached to alkene =CHR 4.5–6.0 Deduce the structures of the two esters D and E and draw their displayed formulae in the boxes below. D C5H10O2 E C5H10O2  The spectrum of D includes a quartet at δ4.1. Identify the protons responsible for this quartet on your structure in by labelling these protons with the letter F. Explain why this peak is split into a quartet.  The spectrum of E has a doublet at δ1.1. Identify the protons responsible for this doublet on your structure in by labelling these protons with the letter G. Explain why this peak has a chemical shift of 1.1.  
9701_w22_qp_43
THEORY
2022
Paper 4, Variant 3
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Questions Discovered
98