CHERRY HILL TUITION OCR A CHEMISTRY A2 PAPER 19 MARK SCHEME ANNOTATIONS MUST BE USED CH 3 CH 3 CH 3 H + correct products

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Eileen Sharp
5 years ago
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1 ERRY ILL TUITIN R A EMISTRY A2 PAPER 19 MARK SEME ALLW Kekulé structures throughout 1 (a) ANNTATINS MUST BE USED ALLW skeletal ALLW + + N 2 R N 2 ALLW 1st curly arrow from the ring R from within the ring to any part of the N + 2 including the + charge + + D NT ALLW intermediate with broken ring less than halfway down: N 2 N 2 N 2 curly arrow from ring to N 2 + correct intermediate curly arrow from bond back to reform ring 1 mark for intermediate correct products 4 + N 2 orseshoe must have open end towards N 2 ALLW Kekulé mechanism: 1 mark for curly arrow N + 2 N 2 N 2 ALLW double bonds shown in other Kekulé arrangement IF has been omitted completely (ie benzene shown), D NT AWARD intermediate mark R products mark (max 2) IF N 2 is shown in incorrect position in intermediate or product, D NT AWARD intermediate mark but award other marks (max 3) 1

2 ERRY ILL TUITIN R A EMISTRY A2 PAPER 19 MARK SEME 1 (b ) ALLW any correct unambiguous structures N 2 ALLW N 2 Note: connectivity is NT being assessed in this part 2 N N 2 N (c) 1st stage isomer: isomer 3 product: 2 N N 2 reagents: Sn AND (conc) l equation: ANNTATINS MUST BE USED ALLW structure of isomer 3 shown separately R in equation ALLW structure of product shown separately R in equation ALLW correct name (3,5-diaminomethylbenzene) IGNRE incorrect name D NT ALLW 6 3 (N 2 ) 2 ALLW Zn + l/ 2 + metal catalyst/lial 4 /Na in ethanol IGNRE NaB 4 ALLW Sn and l followed by Na D NT ALLW Sn and l and Na 12 [] 4 2 IF isomer 3 R product are given in equation but not shown previously then credit here 2 N N 2 2 N N 2 Also credit reagents here if shown (eg above arrow) ALLW correct structural R displayed R skeletal formula ALLW combination of formulae as long as unambiguous 2

3 ERRY ILL TUITIN R A EMISTRY A2 PAPER 19 MARK SEME (c) (i) 2nd stage organic compound: 2 6 D NT ALLW molecular formula ALLW name of compound: propanedioic acid R propane-1,3-dioic acid ALLW absence of e after propan ALLW acyl dichloride: l 2 l ALLW cyclic acid anhydride of propanedioic acid: 2 type of polymer: polyamide ALLW Nylon or Kevlar D NT ALLW polypeptide D NT ALLW amide Total 12 3

4 ERRY ILL TUITIN R A EMISTRY A2 PAPER 19 MARK SEME 2 (a) propane-1,2,3-triol 1 ALLW absence of e after propan ALLW 1,2,3-propanetriol ALLW absence of hyphens 1, 2 and 3 must be clearly separated: ALLW full stops: R spaces: D NT ALLW (b) (i) methanol R ethanol AND renewable 1 BT points required for the mark ALLW correct structural R displayed R skeletal formula D NT ALLW molecular formulae ALLW easy/cheap to manufacture/produce as alternative for renewable/from plants/from fermentation/burns more easily/efficiently (b) (ii) equilibrium shifts to right 1 ALLW equilibrium shifts in forward direction ALLW more products form ALLW greater yield R fully reacts R goes to completion D NT ALLW improves atom economy 4

5 ERRY ILL TUITIN R A EMISTRY A2 PAPER 19 MARK SEME 2 (c) ALLW correct structural R displayed R skeletal formula ALLW combination of formulae as long as unambiguous D NT ALLW molecular formulae ( 2 ) ALLW further esterification, ie ( 2 ) ALLW linear formula for anhydride, ie 2 2 If incorrect carboxylic acid/anhydride/alcohol is used, ALLW EF for second equation 5

6 ERRY ILL TUITIN R A EMISTRY A2 PAPER 19 MARK SEME 2 (d) A B Mark A, B and independently ie 2 column column R R R R R R R R R R R R Total 8 A can be any of the alternatives in the 1st B can be any of the alternatives in the 2nd can be any of the alternatives in the 3rd column ALLW correct structural R displayed R skeletal formula ALLW combination of formulae as long as unambiguous D NT ALLW molecular formulae ALLW correct names for A, B and For B accept diester For, IGNRE n R brackets (even if wrong); ALLW solid side bonds Minimum is one correct repeat unit. Polymer must be open at both ends 6

7 ERRY ILL TUITIN R A EMISTRY A2 PAPER 19 MARK SEME 3 (a) observation: silver R Ag ALLW black R grey type of reaction: oxidation ALLW redox organic product: 3 3 ALLW correct structural R displayed R skeletal formula ALLW combination of formulae as long as unambiguous D NT ALLW molecular formulae ALLW carboxylate, 3 (b) R R intermediate R products (+ ANNTATINS MUST BE USED ALLW mechanism showing curly arrows from lone pair on and of intermediate 1 mark for curly arrow from to of = 1 mark for correct dipole on = AND curly arrow from double bond to 1 mark for correct intermediate with negative charge on AND curly arrow from to of AND curly arrow from to of 1 mark for correct organic product 4 Dipole not required on D NT ALLW incorrect dipole on ALLW 1 mark for correct intermediate with charge on AND curly arrow from to + IGNRE missing D NT ALLW incorrect second product 7

8 ERRY ILL TUITIN R A EMISTRY A2 PAPER 19 MARK SEME 3 (c) reagent: 2 D NT ALLW EF from incorrect reagent, eg 2,4-DNP observation: decolourised R orange to colourless D NT ALLW goes clear ALLW red/orange/yellow/brown in any combination organic product: 3 3 ALLW organic product from reaction of one of the double bonds only, ie 3 3 R ALLW correct structural R displayed R skeletal formula ALLW combination of formulae as long as unambiguous D NT ALLW molecular formulae ALTERNATIVE reagents For 1st mark, ALLW 2 R l 2 R I 2 R l R R I R 2 For 2nd mark, there must be a statement of no change R no observation or similar that implies there is no visible change EXEPT for I 2 which has an observation of decolourised R brown to colourless Total 10 For 3rd mark, correct organic product must be shown that could be from reaction of both or one of the double bonds. 8

9 ERRY ILL TUITIN R A EMISTRY A2 PAPER 19 MARK SEME 4 (a) (i) l( ) + 3N 3 2 N( ) + N N 4 l 1 ALLW use of two N 3 : l( ) + 2N 3 2 N( ) + N l ALLW products as above R 2 N( ) + N 4 l ALLW use of one N 3 : l( ) + N 3 2 N( ) l ALLW products as above R 2 N( ) + l For alternatives below, for N 4 l, ALLW N 4 + l R N l for l, ALLW + l R + + l for 2 N( ) + N 4 + ALLW 2 N( ) N 4 + R 2 N( )N 4 ALLW R in equation in place of (either or both sides) ALLW correct structural R displayed R skeletal formula ALLW combination of formulae as long as unambiguous D NT ALLW molecular formulae (a) (ii) N ALLW correct structural R displayed R skeletal formula ALLW combination of formulae as long as unambiguous 1 ALLW product from carboxylate ion as nucleophile: 2 N 9

10 ERRY ILL TUITIN R A EMISTRY A2 PAPER 19 MARK SEME 4 (b) (i) R D NT ALLW any structure containing R (except in ) 1 (b) (ii) 2 2 ALL bond linkages must be correct, eg the chiral must be linked to the of the, the of the 2 and the N of the N 2 (connectivity is being tested) 2 N N 2 2 The 2nd mark is for the mirror image of an amino acid. This could be any amino acid EXEPT glycine D NT penalise connectivity more than once ALLW R in equation in place of 2 (either or both sides) Each structure must have four central bonds, with at least two wedges, one in; one out For bond into paper, accept: 4 (c) Disadvantages Any two from: (one stereoisomer might have harmful) side effects reduces the (pharmacological) activity/effectiveness cost R difficulty in separating stereoisomers 2 max ANNTATINS MUST BE USED ALLW optical isomer R enantiomers as alternative for stereoisomers ALLW a response that implies an increased dose Synthesis of a single optical isomer Any two from: using enzymes or bacteria using a chiral catalyst R transition metal complex/transition metal catalyst using chiral synthesis R chiral starting material R natural amino acid 2 max Total 8 ALLW biological catalyst ALLW 'chiral pool' R L-amino acids R D-sugars 10

11 ERRY ILL TUITIN R A EMISTRY A2 PAPER 19 MARK SEME 5 (a) (i) Adsorption (onto the stationary phase) ALLW adsorbtion or adsorb(s) or adsorbed spelled correctly at least once Quality of Written ommunication 1 D NT ALLW anything that begins with ab... Adsorption must be spelled correctly (a) (ii) ALLW any value in the range IGNRE significant figures D NT ALLW fraction/percent as final answer (a) (iii) Spot may contain more than one compound/component 1 ALLW compounds have similar R f values/adsorptions R compounds have not (fully) separated R B is spread over a large region R compounds are similar IGNRE retention times 5 (b) (i) G separates the components/compounds ALLW chromatography for G ALLW they have different retention times (ii) (iii) (iv) AND MS is compared to a database/reference 1 nerol and geraniol AND they are stereoisomers R primary alcohols 1 stereoisomers have the same structural formula AND different 3D arrangements 1 1 ALLW MS analyses compounds/gives structural information/gives different mass spectra ALLW (uses) fragmentation patterns/fragments/peaks/parts of the compound D NT ALLW MS identifies compounds (in question) D NT ALLW molecular ion alone/m r etc. ompounds AND reason required for the mark ALLW they are E/Z isomers R cis-trans isomers ALLW straight-chain alcohols R unsaturated alcohols BT points required for the mark ALLW different arrangements in space ircle must include the correct = double bond AND must not extend further than the adjacent atoms in the main chain, ie limit is: 11

12 ERRY ILL TUITIN R A EMISTRY A2 PAPER 19 MARK SEME 5 (c) (b) (v) * * * orrectly calculates amount of myrcene = 34/136 R 0.25 (mol) orrectly calculates 60% yield of menthol = /100 R 0.15 (mol) 2 orrectly calculates mass of menthol = = 23.4 (g) 3 ALL TREE chiral centres required for 2 marks ANY TW chiral centres required for 1 mark If more than three asterisks are shown, mark incorrect asterisk(s) first ANNTATINS MUST BE USED ALLW amount of myrcene 60/100 ALLW amount of menthol 156 ALLW alternative approach based on reacting masses (using same EF principles as above): correctly calculates mass of myrcene that could be obtained from 34 g myrcene: mass = /136 = 39 (g) 156 ; % of 39 g = 39 60/100 = 23.4 (g) ALLW final answer to 2 or more significant figures correctly rounded orrect answer of 23.4 (g) with no working scores all 3 marks Total 12 12

13 ERRY ILL TUITIN R A EMISTRY A2 PAPER 19 MARK SEME 6 (a) ANNTATINS MUST BE USED a singlet for position 2 R a singlet because it has no adjacent s A triplet for positions 4 and 6 R a triplet because it has 2 adjacent s A quintet for position 5 R a quintet because it has four adjacent s 3 ALLW a response that implies a single peak R no splitting ALLW a response that implies a splitting into three D NT ALLW implications of more than one triplet ALLW pentet R a response that implies a splitting into five R multiplet ALLW 1 mark for singlet and triplet and quintet/pentet/multiplet with no identification of protons Any suggestion that the oxygens cause a splitting scores a maximum of 2 marks. All 3 remaining splitting patterns correct 2 marks. Any 2 correct 1 mark. IF number labels for protons in diagram are not identified, ALLW identification by chemical shifts for 2 marks max: singlet at AND a triplet at quintet/pentet/multiplet at lear and unambiguous identification of the protons other than by position number should be credited, ie 2 between two oxygens Quality of Written ommunication singlet R triplet R quintet R pentet R multiplet (see Guidance) must be spelled correctly at least once 13

14 ERRY ILL TUITIN R A EMISTRY A2 PAPER 19 MARK SEME F324 Mark Scheme January (b) ANY 5 marks plus correct structure (in box) ANNTATINS MUST BE USED Molecular ion/m + peak at (m/z of) 106 Fragment peak at 91 is / ALLW molecular mass R relative molecular mass ALLW 6 4 / ALLW peak at 91 represents loss of Molecular formula is 8 10 (or implied, ie any one of the structures below) 2 5 ALLW correct structural R displayed R skeletal formula ALLW combination of formulae as long as unambiguous ALLW a correct name eg a dimethylbenzene ALL FUR structures needed for 1 mark ALLW correct names 13 NMR spectrum shows 5 environments Peak near 20 is a attached at another carbon, R peaks at ~ for aromatic s ALLW NMR spectrum shows five different types of carbon D NT ALLW NMR spectrum has five peaks the mark is for realising what the peaks show, not for just describing the spectrum 14 14

15 ERRY ILL TUITIN R A EMISTRY A2 PAPER 19 MARK SEME Mark Scheme January (b) Number of peaks for other three isomers matched to structures: Any 2 correct for 2 marks 1 correct for 1 mark peaks 3 peaks 6 peaks ALLW carbon environments for peaks orrect structure shown: 6 Total

1 (a) (CH 3 CO) 2 O + CH 3 CH(OH)CH 3 CH 3 COOCH(CH 3 ) 2 + CH 3 COOH

1 (a) (CH 3 CO) 2 O + CH 3 CH(OH)CH 3 CH 3 COOCH(CH 3 ) 2 + CH 3 COOH Question er Mark Guidance 1 (a) ( 3 ) 2 + 3 () 3 3 ( 3 ) 2 + 3 1st mark orrect structure of ester: 3 ( 3 ) 2 2nd mark Equation contains correct formulae for ( 3 ) 2, 3 () 3 AND 3 2 ALLW correct structural