Edexcel Jan 2017 (IAL) Paper 2 Q21

Answers available below

SECTION C Answer ALL the questions. Write your answers in the spaces provided. 21 Grass is similar to many other plants in naturally releasing mixtures of volatile organic compounds. Freshly-cut grass has a characteristic aroma because of the increased release of these compounds, which are known as green leaf volatiles (GLVs). The most important contributors to this aroma are alcohols and aldehydes containing six carbon atoms. The main compound giving freshly-cut grass its smell is Z-hex-3-enal. The human nose can detect Z-hex-3-enal at levels as low as 1.0 ng dm3 or 1.0109 g dm3. However, this compound is relatively unstable and rearranges to form the E isomer. Some other GLVs are methanol, ethanol, Z-hex-3-en-1-ol and E-hex-2-enal. It has been suggested that the release of these GLVs is part of a defence response by the plant. In one study of plants attacked by caterpillars, the chemical composition of the GLVs changed to attract the natural insect predators of these caterpillars. (a) Give the molecular formula of Z-hex-3-enal. (1)(b) Draw the skeletal formula of the E-isomer of hex-3-enal. (1) 20 *P48368A02024* D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A<br /> (c) An average nasal cavity has a volume of 30 cm3. Calculate the minimum number of molecules of Z-hex-3-enal that could be detected in this volume. Data: Avogadro constant = 6.021023 mol1 Molar mass of Z-hex-3-enal = 98 g mol1 (2) (4) Name (d) Complete the table with saturated, straight-chain alcohols having six carbon atoms that could be GLVs by giving one example in each case. Structural formula Classification of alcohol Primary Secondary A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D (e) The compound 2-chloro-2-methylpentane has six carbon atoms. (i) It can be converted into a tertiary alcohol with aqueous sodium hydroxide. Complete the equation for this reaction. (1) CH3 CH3 C CH2 CH2 CH3 +(cid:111) +Cl (ii) What class of reagent is the hydroxide ion in this reaction? (1)*P48368A02124* 21 Turn over<br /> (iii) In different conditions, 2-chloro-2-methylpentane undergoes an elimination reaction that produces an alkene. Complete the reaction mechanism with the appropriate curly arrow. State the essential condition for this reaction. (4) :OH H3C H3C C CH CH2 CH3 Cl D O N O T W R I T E I N T H I S A R E A Essential condition for reaction(f) Methanol and ethanol are both GLVs. There are a number of fragment peaks which appear in the mass spectra of both compounds but, somewhat surprisingly, the OH+ peak at m / e = 17 is not one of them. 22 (i) Suggest the formulae and m / e values of two fragment ions that you would expect to occur in both spectra. First fragment ion Second fragment ion(ii) Give the formula of one fragment ion that you would expect to be present in the mass spectrum of ethanol but absent from that of methanol. (2) (1) *P48368A02224* D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A<br /> A E R A S I H T N I E T I R W T O N O D *(g) Z-hex-3-en-1-ol is only sparingly soluble in water but completely miscible with ethanol. By reference to intermolecular forces, fully explain this difference in solubility. Detailed explanations of the forces involved are not required. (4)A E R A S I H T N I E T I R W T O N O D(Total for Question 21 = 21 marks) TOTAL FOR SECTION C = 21 MARKS TOTAL FOR PAPER = 80 MARKS A E R A S I H T N I E T I R W T O N O D *P48368A02324* 23<br />

Show answer