17.1. Aldehydes and ketones
A subsection of Chemistry, 9701, through 17. Carbonyl compounds
Listing 10 of 304 questions
Describe structural isomerism. A and B are structural isomers with molecular formula C5H10O. They are both straight-chained molecules with only one functional group. Table 5.1 describes observations when separate samples of A and B are added to different reagents. Table 5.1 reagent A B 2,4-dinitrophenylhydrazine (2,4-DNPH reagent) orange precipitate appears orange precipitate appears Tollens’ reagent silver mirror appears no reaction alkaline I2no reaction no reaction Name the functional group present in both A and B. Draw the structures of A and B in the boxes. A B C is a structural isomer of A and B. C is straight chained and has two functional groups. C shows only one type of stereoisomerism. Table 5.2 describes observations when separate samples of C are added to different reagents. Table 5.2 reagent C 2,4-dinitrophenylhydrazine (2,4-DNPH reagent) no reaction Br2orange to colourless alkaline I2yellow precipitate appears Draw the structure of C in the box. C Name the type of stereoisomerism shown by molecules of C. D reacts in the presence of a sulfuric acid catalyst to form E and water. The structure of E is shown in . O E O Name the functional group present in E. Identify the type of reaction that occurs when D reacts to form E. Draw the structure of D in the box. D The infrared spectrum of E is shown in . transmittance / % wavenumber / cm–1 Table 5.3 bond functional groups containing the bond characteristic infrared absorption range (in wavenumbers) / cm–1 C–O hydroxy, ester 1040–1300 C=C aromatic compound, alkene 1500–1680 C=O amide carbonyl, carboxyl ester 1640–1690 1670–1740 1710–1750 C≡N nitrile 2200–2250 C–H alkane 2850–2950 N–H amine, amide 3300–3500 O–H carboxyl hydroxy 2500–3000 3200–3600 Use and Table 5.3 to predict two differences in the absorptions above 1500 cm–1 of the infrared spectrum of D compared to E. Explain your answer.
9701_s23_qp_22
THEORY
2023
Paper 2, Variant 2
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V shows stereoisomerism. V O O O Explain what is meant by stereoisomerism. Deduce the number of stereoisomers of V. Explain your reasoning. Deduce the molecular formula of V. Name all the functional groups present in V. shows two reactions involving V. W X V + reagent T reaction 1 + reagent U reaction 2 O O O OH O OH O O O Identify the role of reagent T for each functional group that reacts in reaction 1. Suggest the identity of reagent U in reaction 2. Both functional groups in one molecule of Y react with an inorganic reagent to form one molecule of Q and one molecule of methanol, CH3OH, as shown in . inorganic reagent Y Q + CH3OH O O O Part of the mass spectrum for Q is shown in . Only peaks with m / e greater than 198 are shown. 198 199 200 x m / e relative abundance Calculate the relative abundance, x, of the peak at m / e = 201. Show your working. x = Q contains only hydroxyl functional groups. Complete Table 6.1 to show the observations that occur when 2,4-dinitrophenylhydrazine (2,4-DNPH reagent) is added to separate samples of Y and Q. Table 6.1 observation on addition of 2,4-DNPH reagent Y Q Under certain conditions, 0.0020 mol of Q reacts with an excess of sodium to produce a total of 44.8 cm3 of gas at s.t.p. Calculate the number of hydroxyl groups present in a molecule of Q. Show your working. number of hydroxyl groups = Use Table 6.2 to describe and explain two differences between the infrared spectrum of Y and Q in the region above 1500 cm–1. Table 6.2 bond functional groups containing the bond characteristic infrared absorption range (in wavenumbers) / cm–1 C–O hydroxy, ester 1040–1300 C=C aromatic compound, alkene 1500–1680 C=O amide carbonyl, carboxyl ester 1640–1690 1670–1740 1710–1750 C≡N nitrile 2200–2250 C–H alkane 2850–2950 N–H amine, amide 3300–3500 O–H carboxyl hydroxy 2500–3000 3200–3650
9701_s24_qp_21
THEORY
2024
Paper 2, Variant 1
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