ALLOW CO 2 and CO 2 H CH 3

Size: px

Start display at page:

Download "ALLOW CO 2 and CO 2 H CH 3"

Sharyl Chambers
5 years ago
Views:

1 CERRY ILL TUITI CR A CEMISTRY A PAPER 1 MARK SCEME 1 (a) (i) The p R point at which the zwitterion exists 1 ALLW p/point at which there is no overall/net charge IGRE p/point at which there is no charge/ neutral charge ie overall/net is required ALLW p/point at which contains C AD 3 + (ii) 3 C C 3 C C ALLW C 3 C( 3 ) + C ALLW C 3 C( 3 ) + C ALLW C and C C 3 C 3 ALLW + charge on or : ie + 3 or 3 + D T ALLW charge on C: ie C D T ALLW or C 3 missing ALLW correct structural R displayed R skeletal formula ALLW combination of formulae as long as unambiguous 1

2 CERRY ILL TUITI CR A CEMISTRY A PAPER 1 MARK SCEME 1 (a) (iii) p < 3: C ALLW carboxyl group R carboxylic acid D T ALLW acid R just carboxylic (without acid ) p > 10: ALLW amino group R amine D T ALLW if give correct formula but wrong name or correct name and wrong formula eg and amide IF any carbon chain is shown attached to BT functional groups ALLW 1 mark eg C C AD C for 1 mark C 3 C AD C 3 for 1 mark RC AD R for 1 mark (b) IF functional groups are shown the wrong way round, ALLW 1 mark i.e. C D T ALLW more repeat units IGRE brackets and n ALLW end bonds shown as D T ALLW if end bonds are missing peptide link must be fully displayed, i.e. ALLW terminal on right (R C= on left), ie TW repeat units shown correctly IF peptide bond is shown not displayed, i.e. C, nd mark can still be awarded

3 CERRY ILL TUITI CR A CEMISTRY A PAPER 1 MARK SCEME 1 (c) (i) There is no chiral carbon ALLW there is no asymmetric carbon R there is no asymmetry in the molecule 1 R it has no non-superimposable mirror image R there are not four different atoms/groups of atoms (attached to carbon) R there are only three different atoms/groups of atoms (attached to carbon) R because there are two hydrogen atoms on the carbon (ii) ALLW Add the same 3-D structure repeated but with groups swapped as after rotation the nd isomer is a mirror image of the first, i.e. Connectivity: Chiral C must be linked to the C of the C, the C of the C S and the of the (ie connectivity is being tested) ie, ALLW as in the example but D T ALLW an attempted shown as below: The nd mark is for the mirror image of CRRECT optical isomer only CARE: may be orientated differently D T penalise connectivity more than once Each structure must have four central bonds, with at least one wedge in AD one wedge out 3

4 CERRY ILL TUITI CR A CEMISTRY A PAPER 1 MARK SCEME For bond into plane of paper, ALLW: For bond out of plane of paper, a solid wedge is expected, either way around: ALLW a hollow wedge for in bond R an out bond, provided it is different from the other in or out wedge eg: ALLW examples of other 3-D representations provided they are possible: i.e. CARE: This is a 3-D representation so this is possible and the bonds are clearly not 90º to one another 4

5 CERRY ILL TUITI CR A CEMISTRY A PAPER 1 MARK SCEME 1 (c) (iii) ATATIS MUST BE USED Disadvantages: any two from: (one stereoisomer might have harmful/adverse) side IGRE harmful/adverse effects only effects reduces the (pharmacological) activity/effectiveness cost of separating stereoisomers R difficulty in separating stereoisomers ALLW a response that implies an increased dose IGRE it takes time to separate Synthesis of a single optical isomer any two from: using enzymes or bacteria using (chemical) chiral synthesis R using chiral catalysts using (natural) chiral molecules/compounds ALLW biological catalysts ALLW chiral transition metal complex/catalyst R stereoselective transition metal complex/catalyst ALLW 'chiral pool' R L-amino acids / D-sugars Quality of Written Communication For full marks to be awarded for this question chiral R enzyme R bacteria R catalyst must be spelled correctly at least once in the correct context 5

6 CERRY ILL TUITI CR A CEMISTRY A PAPER 1 MARK SCEME 1 (d) amino acid isoleucine leucine tyrosine number of peaks mark for each number (e) ALLW correct structural R displayed R skeletal formula ALLW combination of formulae as long as unambiguous Common errors: Look for on first structure and on second structure valine anhydride proline anhydride Total 19 6

7 CERRY ILL TUITI CR A CEMISTRY A PAPER 1 MARK SCEME (a) (i) Response requires three stages Acceptable sequence of stages are: chlorination nitration, reduction, chlorination nitration nitration, chlorination, reduction, reduction chlorination, nitration, reduction Reduction must be a later stage than nitration Mark according to which sequence chosen. Stage 1 organic product: Cl R chemicals: Cl AD AlCl 3 R 3 AD S 4 Stage organic product: Cl R For organic products, ALLW C 6 5 R C 6 5 Cl R C 6 5 ALLW AD D T ALLW ClC 6 4 (formula ambiguous) D T ALLW molecular formulae IGRE any additional structures shown eg - (ortho) and 3- (meta) substituted isomers In chemicals boxes, IGRE temperatures IGRE catalyst For chlorination chemicals, ALLW Cl AD FeCl 3 R Cl AD Fe R Cl AD halogen carrier For nitration chemicals, concentrated not required for 3 R S 4 BUT... D T ALLW dilute chemicals: 3 AD S 4 R Sn AD Cl Stage 3 chemicals: Cl AD AlCl 3 R Sn AD Cl 5 For reduction chemicals, concentrated Cl not required but D T ALLW dilute For Sn/Cl ALLW addition of a also IF it is clear that it is a second step BUT. D T ALLW Sn AD Cl AD a IGRE catalyst 7

8 CERRY ILL TUITI CR A CEMISTRY A PAPER 1 MARK SCEME (a) (ii) diazonium ion ALLW + sign up to halfway along triple bond from left-hand Cl group MUST be displayed IGRE presence of Cl D T ALLW Cl substituent on benzene ring D T ALLW: Cl azo dye Cl = group MUST be displayed In azo dye, ALLW as alternative to phenol group: R a + R a ALLW phenol part substituted at any carbon (ie,3 or 4 position for ) i.e. IGRE geometry/shape, i.e. ALLW = Mark independently D T ALLW if Cl is missing from benzene ring in EITER structure 8

9 CERRY ILL TUITI CR A CEMISTRY A PAPER 1 MARK SCEME (b) δ mark S δ+ S mark 1 step 1 mark 4 + intermediate = mark 3 4 ATATIS MUST BE USED mark 1 curly arrow from π-delocalised ring in benzene to S δ+ in S 3 ALLW curly arrow from the ring R from within the ring mark curly arrow from one S= double bond to the (to produce a S ) ALLW curly arrow to any in S 3 mark 3 intermediate showing delocalisation over 5 carbons Intermediate must have correct S 3 structure FULLY displayed D T ALLW intermediate with broken ring less than halfway up in correct orientation: + mark 4 curly arrow from C bond reforming π- delocalised ring in benzene Stand alone mark IGRE responses after STEP 9

10 CERRY ILL TUITI CR A CEMISTRY A PAPER 1 MARK SCEME ALLW Kekulé mechanism δ mark S δ+ S mark 1 mark 4 step 1 + intermediate = mark 3 ALLW double bonds shown in other Kekulé arrangement (c) (i) Various possibilities, eg: Br ALLW 1,, 3 or 4 Br atoms substituted on phenol ring at carbon atoms, 3, 5 or 6 BUT must be in correct position shown D T ALLW or a 3 C C ALLW for side chain: C 3 C but aromatic part of structure must be shown Br IGRE any additional inorganic products in boxes (even if incorrect Reaction with a ALLW a R as alternative to a + D T ALLW a R a (i.e. a without charge) 3 C C - a + a must be in correct position shown ALLW for side chain: C 3 C but aromatic part of structure must be shown IGRE any additional inorganic products in boxes (even if incorrect) 10

11 CERRY ILL TUITI CR A CEMISTRY A PAPER 1 MARK SCEME (c) (ii) ydrolysis with a(aq) n BT structures, ALLW a R as alternative to a + D T ALLW a R a (i.e. a without charge) 3 C C - a + a must be in correct position shown on nd structure ALLW C 3 Ca/ C 3 C a R C 3 C / C 3 C - a + ALLW one mark for carboxylic acid AD phenol, rather than sodium salts: Mark independently 3 C C ALLW, C 3 Total 15 IGRE any additional inorganic products in boxes (even if incorrect) 11

12 CERRY ILL TUITI CR A CEMISTRY A PAPER 1 MARK SCEME 3 (a) (i) ne mark is for positive carbonyl test (Add),4-dinitrophenylhydrazine AD orange/yellow/red precipitate ALLW errors in spelling ALLW,4(-)DP R,4(-)DP ALLW Brady s reagent or Brady s Test ALLW solid R crystals R ppt as alternatives for precipitate ne mark is for negative aldehyde test EITER (Add) Tollens reagent/tollens test AD no change R no reaction R no silver (mirror) ALLW Ag 3 / 3 (Formulae must be correct) R ammoniacal silver nitrate ALLW Fehling s solution R Benedict s solution AD no (brick-red) precipitate ALLW any response that implies that nothing happens ie no change R no reaction R no silver (mirror) ALLW the aldehyde/pentanal gives a silver mirror (ii) R (Add) S 4 AD K Cr 7 AD no change R no reaction R no green colour 1st mark Take melting point of orange crystals/derivative/product from,4-dp ALLW + AD Cr 7 (Formulae must be correct) ALLW any response that implies that nothing happens IGRE responses using ab 4 (as no observations) TE: a(ii) is marked completely independently of a(i) nd mark Compare melting point with known values R compare melting point with value in database/reference book Mark independently of response for 1st mark D T ALLW 1st or nd marks for taking and comparing boiling points R chromatograms 1

13 CERRY ILL TUITI CR A CEMISTRY A PAPER 1 MARK SCEME 3 (b) (i) Synthesis 1 6 TE: ALL Structures MUST have s shown IGRE bond angles D T ALLW more than one repeat unit C C C IGRE brackets and n Ester linkage must be fully displayed ALLW terminal on right (R C= on left), i.e. C C C ALLW end bonds shown as D T ALLW if structure has no end bonds Synthesis C C C C C C 13

14 CERRY ILL TUITI CR A CEMISTRY A PAPER 1 MARK SCEME Synthesis 3 Mark each structure independently must be connected correctly on BT structures C C C C C C D T ALLW more repeat units IGRE brackets and n C C C C C C ALLW terminal on right (R C= on left), i.e. C C C C C C ALLW end bonds shown as D T ALLW if structure has no end bonds D T ALLW ECF from wrong structure in previous boxes 3 (b) (ii) Synthesis 1: condensation AD Synthesis : addition AD Synthesis 3: condensation Total 11 1 All three correct responses required for the mark 14

15 CERRY ILL TUITI CR A CEMISTRY A PAPER 1 MARK SCEME 4 (a) (C 3 C) + C 3 C()C 3 C 3 CC(C 3 ) + C 3 C 1st mark Correct structure of ester: C 3 CC(C 3 ) nd mark Equation contains correct formulae for (C 3 C), C 3 C()C 3 AD C 3 C ALLW correct structural R displayed R skeletal formula ALLW combination of formulae as long as unambiguous D T ALLW molecular formulae ALLW (C 3 ) CCC 3 R (C 3 ) CCC 3 (b) (i) (relative) solubility 1 IGRE partition (ii) The esters would have similar retention times AD similar structures/molecules R same functional groups R similar polarities R similar solubilities Alcohol would have short retention time AD alkane would have long retention time D T ALLW adsorption R absorption IGRE similar properties 15

16 CERRY ILL TUITI CR A CEMISTRY A PAPER 1 MARK SCEME 4 (c) Elemental analysis and molecular formula marks Use of percentages (to find EF) AD 144 Molecular formula = C 8 16 marks ATATIS MUST BE USED Working C : : = 66.63/1 : 11.18/1 :.19/ : : : 8 : 1 Alternative method: carbon: (144 x 66.63/100)/1 = 8 hydrogen: (144 x 11.18/100)/1 = 16 oxygen: (144 x.19/100)/16 = ester structure 4 marks C 3 3 C C C C C C 3 C 3 4 marks ALLW correct structural R displayed R skeletal formula ALLW combination of formulae as long as unambiguous ECF from earlier structures If not fully correct award following marks: If structure an ester of formula C 8 16 R the organic structure contains C(C 3 ) 3 If structure is an ester of formula C 8 16 AD ester contains C(C 3 ) 3 If structure is an ester of formula C 8 16 AD ester contains C C(C 3 ) 3 AD ester contains C 3 C C i.e. If the ester link is reversed C 3 C 3 C C C C C 3 IGRE any name C 3 16

17 CERRY ILL TUITI CR A CEMISTRY A PAPER 1 MARK SCEME F34 Mark Scheme January 01 MR analysis 4 marks TE: Each peak can be identified from: its δ value: ± 0. ppm a range, eg the peak between and 3 its relative peak area (CARE two peaks have an area of ) its splitting (CARE: two peaks are singlets) labelling on the spectrum Triplet (at δ 1.3) shows an adjacent C R triplet (at δ 1.3) shows (C with) adjacent s/protons (because of splitting: so triplet) QWC: triplet must be spelled correctly ALLW neighbouring s for adjacent to s Peak at (δ). shows adjacent to C= AD adjacent to (C with) no hydrogens (because of no splitting: so singlet) For peak at (δ). ALLW singlet at (δ). ALLW singlet labelled Peak at (δ) 4. shows C AD adjacent C 3 R 3 adjacent s/protons (because of splitting: so quartet) Peak at (δ) 0.9 show 3 x C 3 (because of singlet and area 9) 4 marks Total for 4(c) 10 Total 15 For peak at (δ) 4. ALLW quartet (labelled ) Check back for any responses added to spectra ADD ^ MARK T TE SPECTRUM PAGE T SW TAT IT AS BEE LKED AT 19 17

PMT GCE. Chemistry A. Advanced GCE. Unit F324: Rings, Polymers and Analysis. Mark Scheme for January Oxford Cambridge and RSA Examinations

PMT GCE. Chemistry A. Advanced GCE. Unit F324: Rings, Polymers and Analysis. Mark Scheme for January Oxford Cambridge and RSA Examinations GCE Chemistry A Advanced GCE Unit F324: Rings, Polymers and Analysis Mark Scheme for January 2012 xford Cambridge and RSA Examinations CR (xford Cambridge and RSA) is a leading UK awarding body, providing