Questions Q1. Part of the infrared (IR) spectrum of a compound is shown. The compound could be A B C D propan-1-ol. propanoic acid. propanal. propanone. Q2. How many molecular ion peaks are in the mass spectrum of 1,2-dichloroethane? Assume the only isotopes present are 1H, 12C, 35Cl and 37Cl. A 4 B 3 C 2 D 1 Q3. Which types of bonds and molecules absorb infrared radiation? (1) Q4. Which two isomeric alcohols, with the formula C4H9OH, would you expect to give a peak due to CH2OH+ in their mass spectra? A B C D butan-1-ol and 2-methylpropan-1-ol. butan-1-ol and 2-methylpropan-2-ol. 2-methylpropan-1-ol and 2-methylpropan-2-ol. butan-1-ol and butan-2-ol. Q5. Samples of the isomers propan-1-ol and propan-2-ol can be identified by mass spectrometry. Only propan-1-ol would be expected to have a significant peak in its mass spectrum at m / e value of A B C D 15 31 45 60 (1) Q6. The mass spectrum of propanal can be clearly distinguished from the mass spectrum of propanone. Only the propanal spectrum has a large peak due to the (1) A C3H6O+, molecular ion, m/e = 58 B C3H5O+ fragment, m/e = 57 C C2H5+ fragment, m/e = 29 D CH3+ fragment, m/e = 15 Q7. Which statement about propanal, CH3CH2CHO, and propanone, CH3COCH3 is not correct? The compounds have A B C D a different fingerprint region in the infrared spectrum. an absorption in the infrared spectrum due to the carbonyl group. different fragmentation patterns in the mass spectrum. molecular ion peaks at different mass to charge ratios. (1) Q8. Some organic molecules, either on their own or as part of a mixture, contribute to some very unpleasant odours. The molecule shown below, commonly called isovaleric acid, is responsible for the smell of sweaty feet. Isovaleric acid can be used to produce esters that have important industrial uses in the pharmaceutical industry, as sedatives and tranquilizers, and in the food industry, as flavouring and fragrance additives. The molecule with the systematic name (5α)-androst-16-en-3-one, labelled X in this question, is found in human sweat and urine. However, in other situations, these molecules can induce a very different effect. For example, X is present in commercial products used by pig farmers to determine when sows are ready for mating. (a) What is the systematic name for isovaleric acid? (1) ............................................................................................................................................. (b) What is the molecular formula of isovaleric acid? (1) ............................................................................................................................................. (c) Isovaleric acid has three structural isomers which are also carboxylic acids. One of these acids is drawn in the first box below. In the empty boxes below, draw the structures, using skeletal formulae, of the other two carboxylic acid structural isomers of isovaleric acid. (2) (e) Isoamyl alcohol is the alcohol from which isovaleric acid can be produced directly. This alcohol forms intermolecular hydrogen bonding. Using the simplified representation R–O–H, draw a hydrogen bond between two alcohol molecules and clearly indicate the bond angle about the hydrogen involved in the hydrogen bond. (2) (f) There are also London forces between molecules of isoamyl alcohol. *(i) Describe how London forces are formed. (2) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. (ii) The straight-chain structural isomer of isoamyl alcohol has a boiling temperature of 138°C. Suggest whether the boiling temperature for isoamyl alcohol will be higher than, lower than or the same as the straight-chain isomer. Justify your choice. (3) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. (g) The molecule identified as X in the introduction to this question, can be formed from the alcohol Y shown below. (i) The oxidation of an alcohol of this type with acidified sodium dichromate(VI) could involve either reflux or distillation. Explain why either could be used in this case. (1) ............................................................................................................................................. ............................................................................................................................................. (ii) An alternative reagent for the oxidation of an alcohol is acidified potassium manganate(VII), KMnO4. However, this is likely to produce other products because X contains another functional group that could react with this reagent. Name this other functional group in X and suggest the type of molecule formed in its reaction with acidified potassium manganate(VII), KMnO4. (2) Functional group that reacts ............................................................................................................................................. Type of molecule formed ............................................................................................................................................. *(h) Isovaleric acid and alcohol Y could react together to produce a compound with a pleasant aroma, but this can be masked by even a small residue of the starting molecules. Generally, spectroscopic methods are much more reliable than sense of smell in detecting the presence of molecules. The infrared absorption ranges associated with some functional groups are given below. By quoting appropriate data, describe how both infrared spectroscopy and mass spectrometry could be used to determine the presence of isovaleric acid. The skeletal formula of isovaleric acid is shown below. (4) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. Q10. Alcohols, such as ethanol, undergo a number of reactions. (a) Write the balanced equation for the oxidation of ethanol to ethanoic acid. Use displayed formulae to show all the bonds in the reactants and products. Use the symbol, [O], to represent an oxygen atom from the oxidizing agent. State symbols are not required. (3) (b) Ethanol can be oxidized to the aldehyde, ethanal, using the apparatus shown below. (i) State the class of alcohols that can be oxidized to aldehydes. (1) ............................................................................................................................................. (ii) Explain fully why ethanal, rather than ethanoic acid, is produced and collected when the apparatus in (b) is used. (3) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. (iii) State the purpose of the part of the apparatus labelled A. (1) ............................................................................................................................................. ............................................................................................................................................. (c) (i) The distillation product, ethanal, is dried. What test could you use to show that the dry sample is contaminated by ethanol or ethanoic acid? Suggest one reagent that could be used to test for both ethanol and ethanoic acid in the presence of ethanal. Give the observation that would be seen if either were present. (2) Reagent ............................................................................................................................................. Observation ............................................................................................................................................. (ii) Physical methods can also be used to identify molecules. Give the formula of a fragment that produces a peak in the mass spectrum of ethanal but not in the mass spectrum of ethanol. Identify one feature in the infrared spectrum of ethanal that distinguishes it from ethanol. Wavenumber values are not required. (2) Mass spectrum fragment ........................................................... Infrared spectrum feature ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. (d) Ethanol is a highly flammable liquid. However, some other larger and more complex alcohols can be more difficult to burn. One such example is propane-1,2,3-triol, commonly called glycerol, which has the formula CH2OHCHOHCH2OH or C3H8O3. (i) Write the equation for the complete combustion of propane-1,2,3-triol, using its molecular formula. State symbols are not required. (1) C3H8O3 + → (ii) Write a possible equation for the combustion of propane-1,2,3-triol in a limited supply of oxygen. Suggest a likely observation of this reaction under these conditions. State symbols are not required. (3) C3H8O3 + → Observation ............................................................................................................................................. ............................................................................................................................................. (e) Halogenoalkanes react with aqueous hydroxide ions to form the corresponding alcohol. (i) Name the type of reaction and mechanism. ............................................................................................................................................. (2)
