13.1. Formulas, functional groups and the naming of organic compounds
A subsection of Chemistry, 9701, through 13. An introduction to AS Level organic chemistry
Listing 10 of 266 questions
Organic compounds which contain oxygen may contain alcohol, aldehyde, carboxylic acid, ester or ketone functional groups. The functional groups may be identifi ed by their reactions with specifi c reagents. Compound X has the empirical formula CH2O and Mr of 90. There is no reaction when X is treated with NaHCO3. What functional group does this test show to be not present in X? When 0.600 g of X is reacted with an excess of Na, 160 cm3 of H2, measured at room temperature and pressure, is produced. What functional group does this reaction show to be present in X? Use the data to calculate the amount, in moles, of hydrogen atoms produced from 0.600 g of X. Hence, show that each molecule of X contains two of the functional groups you have given in . When X is warmed with Fehling’s reagent, a brick red precipitate is formed. Treatment of X with 2,4-dinitrophenylhydrazine reagent produces an orange solid. What functional group do these reactions show to be present in X? Draw the displayed formula of this functional group. Use your answers to , and to deduce the structural formula of X. What is the structural formula of the organic product of the reaction of X with Fehling’s reagent? Compound X can be both oxidised and reduced. Give the structural formula of the compound formed when X is reacted with NaBH4 under suitable conditions. Give the structural formula of the compound formed when X is heated under refl ux with acidifi ed K2Cr2O7.
9701_s12_qp_21
THEORY
2012
Paper 2, Variant 1
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Food additives are substances added to food to preserve the fl avour or to improve its taste and appearance. European Union legislation requires most additives used in foods to be labelled clearly in the list of ingredients, either by name or by an ‘E number’. E296 is malic acid which occurs in unripe fruit. Malic acid has the structural formula HO2CCH2CH(OH)CO2H. Some reactions of malic acid are shown below. In the boxes below, give the structural formulae of organic compounds A to F. HO2CCH2CH(OH)CO2H concentrated H2SO4 C F A B heat with CH3CO2H / H+ heat with CH3OH / H+ cold dilute MnO4 – / H+ steam / H3PO4 D E hot concentrated MnO4 – / H+ What type of reaction is each of the following conversions? malic acid into C C into D C into E Suggest one major commercial use of compounds such as A or B. Malic acid is chiral. Draw fully displayed formulae of the two optical isomers of malic acid. Indicate with an asterisk (*) the chiral carbon atom. Compound C also shows stereoisomerism. Draw the skeletal formulae of each of the stereoisomers of C. Label each isomer. The food additive E330 is another organic compound which occurs naturally in fruit. E330 has the following composition by mass: C, 37.5 %; H, 4.17 %; O, 58.3 %. Calculate the empirical formula of E330.
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THEORY
2012
Paper 2, Variant 2
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Many naturally occurring organic compounds contain oxygen. Such compounds may contain alcohol, aldehyde, carboxylic acid, ester or ketone functional groups. These functional groups may be identifi ed by their reactions with specifi c reagents. Compound F is a white solid which has the molecular formula C3H6O3. Compound F is soluble in water. Addition of NaHCO3 to this solution produces a colourless gas, G, which turns lime water milky. What is the identity of the gas G? What functional group does this test show to be present in F? When F is heated with concentrated sulfuric acid, a colourless liquid H is produced. When cold dilute acidifi ed KMnO4 is shaken with H, the solution becomes colourless. What type of reaction occurs when H is formed from F? Use your answers to and to deduce the structural formula of the colourless liquid H. Compound F will react with sodium. Calculate the volume of H2, measured at room temperature and pressure, which will be produced when 0.600 g of F is reacted with an excess of Na. There are two structural isomers of F that give the reactions described in and . Suggest two structural formulae for these isomers. J K Isomers J and K can both be oxidised. What will be produced when each of the isomers J and K is heated under refl ux with acidifi ed K2Cr2O7? product from J product from K
9701_s12_qp_23
THEORY
2012
Paper 2, Variant 3
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NMR and X-ray crystallography are two important analytical techniques which can be used to study the structure and function of molecules. Nuclear magnetic resonance, NMR, arises because protons possess spin which generates a small magnetic moment. When an external magnetic fi eld is applied the protons can align with or against the external fi eld. If they are given a small amount of energy in the radio frequency range each can be ‘promoted’ so that their magnetic moment opposes the external fi eld. Two factors can infl uence the energy required for this promotion. What are they? A compound, J, has the formula C4H10O. The NMR spectrum of J is shown. δ / ppm Indicate the groups responsible for each peak and hence deduce the structure of J. peak at 1.26 δ peak at 2.0 δ structure of J There are three other isomers of J containing the same functional group as J. Draw the structures of two of these three isomers and indicate how many different chemical shifts each would show in its NMR spectrum. isomer 1 isomer 2 number of groups of peaks number of groups of peaks X-ray crystallography can be useful in gathering information about the structure of large organic molecules, such as nucleic acids. Which element will show up most strongly in the X-ray crystallography of a nucleic acid? Explain your answer. X-ray crystallography will not detect hydrogen atoms. Explain why this is so.
9701_s12_qp_42
THEORY
2012
Paper 4, Variant 2
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