22.2. Mass spectrometry
A subsection of Chemistry, 9701, through 22. Analytical techniques
Listing 10 of 98 questions
Describe what is meant by a racemic mixture. Asparagine is an amino acid that contains a chiral carbon atom and displays stereoisomerism. Separate samples of asparagine are dissolved in CDCl 3 and analysed using carbon‑13 and proton (1H) NMR spectroscopy. C C asparagine H2N CH2 NH2 H O OH O C Predict the number of peaks seen in the carbon‑13 and proton (1H) NMR spectra of asparagine. carbon‑13 NMR proton (1H) NMR number of peaks  The isoelectric point of asparagine, asn, is at pH5.4. Describe the meaning of the term isoelectric point. Draw the structure of asparagine at pH1.0.  Asparagine can polymerise to form poly. Draw the structure of poly, showing two repeat units. The peptide linkage should be shown displayed.  The isoelectric point of lysine, lys, is at pH9.8. H2N C lysine H (CH2)4 NH2 COOH A mixture of the dipeptide lys-asn and its two constituent amino acids, asparagine and lysine, is analysed by electrophoresis using a buffer at pH 5.0. The results obtained are shown in Fig.6.3. mixture applied here E F G + – Suggest identities for the species responsible for spots E, F and G. Explain your answers. spot identity E F G  Thin-layer and gas-liquid chromatography can be used to analyse mixtures of substances. Each type of chromatography makes use of a stationary phase and a mobile phase. Complete Table6.1 with an example of each of these. Table 6.1 stationary phase mobile phase thin-layer chromatography gas-liquid chromatography  An unknown amino acid is analysed using thin-layer chromatography. Two chromatographs of the unknown amino acid and four reference amino acids, P, Q, R and S, are obtained using two different solvents. P unknown amino acid solvent 1 Q R S P unknown amino acid solvent 2 Q R S cm Identify the unknown amino acid. Justify your answer. A mixture containing three organic compounds is analysed by gas chromatography and mass spectrometry. The gas chromatogram is shown. peak area / mm2 J J K K L L retention time / minutes The area underneath each peak is proportional to the mass of the respective compound in the mixture. The concentration of K in the mixture is 5.52×10–2 g dm–3. Calculate the concentration, in mol dm–3, of compound L in the mixture. [Mr: L, 116]  concentration of L = mol dm–3 
9701_s22_qp_41
THEORY
2022
Paper 4, Variant 1
View
Describe what is meant by a racemic mixture. Asparagine is an amino acid that contains a chiral carbon atom and displays stereoisomerism. Separate samples of asparagine are dissolved in CDCl 3 and analysed using carbon‑13 and proton (1H) NMR spectroscopy. C C asparagine H2N CH2 NH2 H O OH O C Predict the number of peaks seen in the carbon‑13 and proton (1H) NMR spectra of asparagine. carbon‑13 NMR proton (1H) NMR number of peaks  The isoelectric point of asparagine, asn, is at pH5.4. Describe the meaning of the term isoelectric point. Draw the structure of asparagine at pH1.0.  Asparagine can polymerise to form poly. Draw the structure of poly, showing two repeat units. The peptide linkage should be shown displayed.  The isoelectric point of lysine, lys, is at pH9.8. H2N C lysine H (CH2)4 NH2 COOH A mixture of the dipeptide lys-asn and its two constituent amino acids, asparagine and lysine, is analysed by electrophoresis using a buffer at pH 5.0. The results obtained are shown in Fig.6.3. mixture applied here E F G + – Suggest identities for the species responsible for spots E, F and G. Explain your answers. spot identity E F G  Thin-layer and gas-liquid chromatography can be used to analyse mixtures of substances. Each type of chromatography makes use of a stationary phase and a mobile phase. Complete Table6.1 with an example of each of these. Table 6.1 stationary phase mobile phase thin-layer chromatography gas-liquid chromatography  An unknown amino acid is analysed using thin-layer chromatography. Two chromatographs of the unknown amino acid and four reference amino acids, P, Q, R and S, are obtained using two different solvents. P unknown amino acid solvent 1 Q R S P unknown amino acid solvent 2 Q R S cm Identify the unknown amino acid. Justify your answer. A mixture containing three organic compounds is analysed by gas chromatography and mass spectrometry. The gas chromatogram is shown. peak area / mm2 J J K K L L retention time / minutes The area underneath each peak is proportional to the mass of the respective compound in the mixture. The concentration of K in the mixture is 5.52×10–2 g dm–3. Calculate the concentration, in mol dm–3, of compound L in the mixture. [Mr: L, 116]  concentration of L = mol dm–3 
9701_s22_qp_43
THEORY
2022
Paper 4, Variant 3
View
CompoundF has been found in small quantities in some cereals and dried fruit. O O F OH Cl O N H O O A B Give the name of the functional groups labelled A and B. A B  State the number of chiral carbon atoms in one molecule of F. F can be hydrolysed by heating with an excess of dilute hydrochloricacid, as shown. Three products are formed: G and two others. O O F OH Cl O N H O O Cl excess dilute HCl + + O O G OH OH HO OH Draw the structures of the other products of the reaction in the boxes provided. CompoundH is formed in one step of a different synthesis, as shown. O O OH OH HO O O H OH Cl OH HO Cl 2 and FeCl 3 State the role of FeCl 3 in this step. Use the Data Booklet to suggest two reasons why the chlorine atom in compound H substitutes into the ring at the position shown, instead of the other positions in the ring.  CompoundJ, CxHyOz, is also found in some cereals. Part of the mass spectrum of J is shown. The M and M+1 peaks are labelled, along with their relative intensities. relative intensity m/e M, relative intensity 100.0 M+1, relative intensity 14.4 Calculate the number of carbon atoms, x, present in J.  x = The mass spectrum has a peak at m/e = 205. Suggest the identity of the fragment lost from J to form this peak. 
9701_m20_qp_42
THEORY
2020
Paper 4, Variant 2
View
Procaine is used as an anaesthetic in medicine. It can be synthesised from methylbenzene in fivesteps as shown in Fig.7.1. CH3 methylbenzene COOH NO2 COCl NO2 C O O CH2CH2N(CH2CH3)2 NO2 X steps 1 and 2 step 3 step 5 step 4 SOCl 2 C procaine O O CH2CH2N(CH2CH3)2 NH2 Name all the functional groups present in procaine. A molecule of procaine has 13 carbon atoms. State the number of carbon atoms that are sp, sp2 and sp3 hybridised in procaine. sp carbons = sp2 carbons = sp3 carbons =  The proton (1H) NMR spectrum of procaine dissolved in D2O is recorded. Predict the number of peaks observed. State why procaine can act as a base. CompoundX can be synthesised in two steps from methylbenzene. CH3 methylbenzene COOH NO2 X W step 1 step 2 Draw the structure of compoundW in the box provided. State the reagents and conditions for step1 and step2. step 1 step 2  Procaine is synthesised in three steps from X. Suggest the reagents and conditions for step4 and for step5 in . step 4 step 5  Explain what is meant by partition coefficient, Kpc. The partition coefficient of procaine between octan-1-ol and water is 1.77. Octan-1-ol and water are immiscible. A solution containing 0.500 g of procaine in 75.0 cm3 of water is shaken with 50.0 cm3 of octan‑1‑ol. Calculate the mass of procaine that is extracted into the octan‑1‑ol.  mass of procaine extracted = g 
9701_s22_qp_41
THEORY
2022
Paper 4, Variant 1
View
Procaine is used as an anaesthetic in medicine. It can be synthesised from methylbenzene in fivesteps as shown in Fig.7.1. CH3 methylbenzene COOH NO2 COCl NO2 C O O CH2CH2N(CH2CH3)2 NO2 X steps 1 and 2 step 3 step 5 step 4 SOCl 2 C procaine O O CH2CH2N(CH2CH3)2 NH2 Name all the functional groups present in procaine. A molecule of procaine has 13 carbon atoms. State the number of carbon atoms that are sp, sp2 and sp3 hybridised in procaine. sp carbons = sp2 carbons = sp3 carbons =  The proton (1H) NMR spectrum of procaine dissolved in D2O is recorded. Predict the number of peaks observed. State why procaine can act as a base. CompoundX can be synthesised in two steps from methylbenzene. CH3 methylbenzene COOH NO2 X W step 1 step 2 Draw the structure of compoundW in the box provided. State the reagents and conditions for step1 and step2. step 1 step 2  Procaine is synthesised in three steps from X. Suggest the reagents and conditions for step4 and for step5 in . step 4 step 5  Explain what is meant by partition coefficient, Kpc. The partition coefficient of procaine between octan-1-ol and water is 1.77. Octan-1-ol and water are immiscible. A solution containing 0.500 g of procaine in 75.0 cm3 of water is shaken with 50.0 cm3 of octan‑1‑ol. Calculate the mass of procaine that is extracted into the octan‑1‑ol.  mass of procaine extracted = g 
9701_s22_qp_43
THEORY
2022
Paper 4, Variant 3
View
Questions Discovered
98