Edexcel Jun 2014 (IAL) Paper 4 Q18 (with explained solutions) |

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Edexcel Jun 2014 (IAL) Paper 4 Q18

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Answer ALL the questions. Write your answers in the spaces provided. SECTION B 18 Citronella oil is obtained from lemongrass. It is a source of chemicals for the perfume industry. Three of the aldehydes found in citronella oil are shown below. citronellal geranial (a) Give the molecular formula for citronellal. neral (1)(b) Citronellal has one chiral carbon atom. Draw a circle around the chiral carbon atom on the structure of citronellal below. (1) 10 *P42992A01028*<br />
(c) Geranial and neral are a pair of E-Z isomers. (i) Explain how this type of isomerism arises. (2)(ii) Draw a circle around any part of the geranial structure below that causes its E-Z isomerism. (d) Describe a simple test tube reaction to show that these three carbonyl compounds are aldehydes and not ketones. State the observation you would make. (1) (2)*P42992A01128* 11 Turn over<br />
(e) The skeletal formula of neral is shown below. Draw the skeletal formula for the organic product of the reaction of neral with (i) excess hydrogen in the presence of a nickel catalyst. (ii) lithium tetrahydridoaluminate(III) (lithium aluminium hydride) in dry ether. (1) (1) (Total for Question 18 = 9 marks) 12 *P42992A01228*<br />
BLANK PAGE *P42992A01328* 13 Turn over<br />

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Reject superscripts Mark Section B Question Number 18(a) Acceptable Answers C10H18O ALLOW any order i.e. C10 OH18 /H18 C10O /H18O C10 /OC10H18 / OH18 C10 IGNORE C9H17CHO and other structural formulae as working COMMENT Allow numbers not as subscripts e.g.C10H18O Structural formula without correct molecular formula will not score. Question Number 18(b) Acceptable Answers Reject more than one carbon atom indicated Mark Circle as shown ALLOW * or any other clear indication of the correct carbon atom WCH0401 1406<br />
Acceptable Answers Question Number 18(c)(i) Stand alone marks Mark Reject Just no rotation without reference to C=C molecule does not rotate molecules/compounds attached to C atoms First mark restricted / barrier to rotation around/due to C=C/ bond ALLOW no/lack of/inhibits (free) rotation around/due to C=C/ bond (1) Second mark two different atoms/groups attached to each C in C=C /each C in C=C must not have two groups the same attached to it OR 4 different atoms/groups attached to C=C ALLOW 2 highest priority/molecular mass/atomic number atoms/groups on opposite sides (of C=C) is the E isomer ALLOW 2 highest priority/molecular mass/atomic number atoms/groups on the same side (of C=C) is the Z isomer ALLOW correct diagrams to show any of these points (1) Acceptable Answers Question Number 18(c)(ii) circle around double bond as shown ALLOW any clear indication of the correct double bond or a circle around either of the two carbon atoms in this bond. ALLOW the circle being extended to the adjacent carbon atoms attached to the C=C. Mark Reject both C=C bonds circled the circle extended to include the C=O and/or C-H bond(s) on the right WCH0401 1406<br />
Mark Acceptable Answers Reject reagent Fehlings (solution and heat/boil) Just an Any reagent (1) observation not and matching observation (1) from linked to a reagent observation (blue solution) to red / red-brown/brown /orange and precipitate (blue solution) to red / red-brown/brown /orange and precipitate silver mirror or grey/black/silver and ppt (orange) to green/blue Benedicts (solution and heat/boil) Tollens (reagent) /ammoniacal silver nitrate (and warm) ALLOW potassium/sodium dichromate((VI)) and sulfuric acid (and warm) or acidified dichromate((VI) ions and warm) or acidified (potassium/sodium) dichromate((VI)) ALLOW Schiffs reagent Question Number 18(d) pink/purple/magenta ALLOW correct formulae/ names IGNORE Bradys reagent/2,4- DNPH etc IGNORE sodium hydroxide in Tollens reagent WCH0401 1406<br />
Question Number 18(e)(i) Acceptable Answers Reject Mark In (e)(i) and (e)(ii), penalise any structure other than skeletal only once, in the item where it appears first any structure with an OH group OR ALLOW any unambiguous skeletal formula showing the aldehyde (with or without the H in CHO) Acceptable Answers Question Number 18(e)(ii) In (e)(i) and (e)(ii), penalise any structure other than skeletal only once, in the item where it appears first Reject any structure without both C=C the E isomer Mark ALLOW O for OH ALLOW O-H for OH ALLOW the OH on either side of the structure ALLOW just 1 H shown on the C with the OH attached ALLOW any unambiguous skeletal formula showing the alcohol (with or without the 2Hs on end C) (Total for Question 18 = 9 marks) WCH0401 1406<br />

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