ANNOTATIONS MUST BE USED

Size: px

Start display at page:

Download "ANNOTATIONS MUST BE USED"

Leo Underwood
5 years ago
Views:

1 1 (a) ATATIS MUST BE USED ALLW skeletal ALLW R ALLW 1st curly arrow from the ring R from within the ring to any part of the 2 including the charge H D T ALLW intermediate with broken ring less than halfway down: H curly arrow from ring to correct intermediate curly arrow from C H bond back to reform ring 1 mark for intermediate correct products 4 H Horseshoe must have open end towards ALLW Kekulé mechanism: 1 mark for curly arrow H H ALLW double bonds shown in other Kekulé arrangement IF has been omitted completely (ie benzene shown), D T AWARD intermediate mark R products mark (max 2) IF is shown in incorrect position in intermediate or product, D T AWARD intermediate mark but award other marks (max 3)

2 Question er Mark Guidance 1 (b ) ALLW any correct unambiguous structures ALLW ote: connectivity is T being assessed in this part (c) 1st stage isomer: isomer 3 product: ATATIS MUST BE USED ALLW structure of isomer 3 shown separately R in equation H 2 H 2 ALLW structure of product shown separately R in equation ALLW correct name (3,5-diaminomethylbenzene) IGRE incorrect name D T ALLW C 6 H 3 (H 2 ) 2 reagents: Sn AD (conc) HCl equation: ALLW Zn HCl/H 2 metal catalyst/lialh 4 /a in ethanol IGRE abh 4 ALLW Sn and HCl followed by ah D T ALLW Sn and HCl and ah 12 [H] 4 H 2 IF isomer 3 R product are given in equation but not shown previously then credit here 2 H 2 H 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

3 Question er Mark Guidance (c) (i) 2nd stage organic compound: HC CH 2 CH 6 H D T ALLW molecular formula H ALLW name of compound: propanedioic acid R propane-1,3-dioic acid ALLW absence of e after propan ALLW acyl dichloride: ClC CH 2 CCl ALLW cyclic acid anhydride of propanedioic acid: CH 2 C C type of polymer: polyamide ALLW ylon or Kevlar D T ALLW polypeptide D T ALLW amide Total 12

4 Question Expected Answers Marks Additional Guidance 2 (a) ALLW C 6 H 6 Br 2 C 6 H 5 Br HBr Br 2 Br HBr (b) (i) White precipitate R white solid R white crystals H 1 D T ALLW multiple substitution D T ALLW Br D T ALLW colourless D T ALLW white ppt and bubbles Br Br 2 D T ALLW Br 3 C 6 H 2 H R 2,4,6-tribromophenol R tribromophenol (ii) 1,2-Dibromocyclohexane Br (iii) MUST spell delocalised/delocalized or localised/localized correctly once in the answer to obtain all 5 marks benzene electrons or π-bonds are delocalised phenol a lone or non-bonded pair of electrons on the oxygen or the H group is (partially) delocalised into the ring cyclohexene electrons are localised R delocalised between two carbons benzene has a lower electron density R phenol has a higher electron density R cyclohexene has a higher electron density benzene cannot polarise or induce a dipole in Br 2 R phenol can polarise the Br 2 R cyclohexene can polarise Br 2 or the Br Br bond 1 5 ALLW 1,2dibromocyclohexane R 1-2dibromocyclohexane R 12dibromocyclohexane R cyclo-1,2-dibromohexane D T ALLW dibromocyclohexane R C 6 H 10 Br 2 R structures ALLW diagram to show overlap of all 6 p-orbitals for delocalisation D T ALLW benzene has delocalised structure or ring ALLW diagram to show movement of lone pair into ring for phenol ALLW diagram or description of overlap of 2 adjacent p-orbitals for bonding in cyclohexene D T ALLW cyclohexene has a C=C double bond IGRE slip if cyclohexene is written as cyclohexane but - bonding correctly described D T ALLW charge density R electronegativity instead of electron density ALLW Br R electrophile Br as alternate to polarise

5 (c) ALLW H H 2 H 3 C H H3C H 3 C 5 IGRE Cl - ion D T ALLW if ring is connected to the triple bond in the diazonium or if diazonium has a negative charge ALLW one mark for correct displayed diazonium if alkyl group is not shown ALLW ALLW H 3 C H 3 C 2 ALLW ECF on incorrect amine for both marks for one mark ALLW ALLW H 3 C H 3 C H HCl and temp < 10 o C R a HCl and temp < 10 o C alkaline AD phenol (if temperature stated must be below 10 o C) Total 14 for one mark for one mark ALLW ah R KH & C 6 H 5 H R phenoxide ion R C 6 H 5 ALLW reagents and conditions from the equations

6 3 (a) (i) M1 p-orbitals overlap (to form pi/π-bonds) 4 ATATE ASWER WITH TICKS AD CRSSES ETC IGRE p-orbitals overlap to form sigma bonds M2 π-bond(s) are delocalised in structure B ALLW electrons are delocalised in structure B IGRE B has delocalised structure or ring (must be electrons or π-bonds) M3 π-bonds are localised/between two carbons in structure A M4 ALLW π-electrons/p-orbital overlap localised/between two carbons in structure A ALLW p-orbitals overlap with one other carbon IGRE electrons are localised R structure A has localised structure (must be π-bonds/π-electrons/p-orbital overlap) ALLW labelled diagram showing overlap of p-orbitals between two carbon atoms D T ALLW C=C in this diagram Diagram for structure A must show the full ring for M4 IGRE C=C in M4 diagram AD Diagrams show correct position of delocalised and localised π-bonds/π-electrons R correct position of p-orbital overlap QWC requires delocalised/delocalized spelled correctly and used in correct context IGRE charge density D T ALLW electronegativity Structures do not need to be labelled A and B if the description matches the structure

7 (ii) structure B/delocalised structure is (more) stable 2 ALLW structure B is low in energy IGRE structure B is less reactive structure B is a better because (enthalpy change of hydrogenation for benzene is) less (exothermic) than (-) 357 (kj mol -1 ) ALLW enthalpy change/hydrogenation for benzene is less (negative) than 3 ( )119 IGRE more positive than (-)357 kj mol -1 ALLW enthalpy change is less than 3x enthalpy change for cyclohexene ALLW structure B is more stable by 149 kj mol -1 (2 marks) D T ALLW more/less energy needed for the reaction Answer must refer to data given in the question and must be a comparison IGRE 360 kj mol -1 o marks can be awarded if structure A is selected (b) 2 curly arrow from C bond to curly arrow from lone pair on fluoride ion to positive charge on benzene ring F First curly arrow must come from bond not from C atom ALLW first curly arrow to nitrogen atom R to positive charge on nitrogen atom ALLW second curly arrow from negative charge on fluoride ion ALLW second curly arrow to carbon atom with positive charge

8 (c) ( ) 2 CHBr FeBr 3 ( ) 2 CH FeBr 4 1 ALLW correct structural R displayed R skeletal formulae R a combination of above as long as unambiguous ALLW positive charge anywhere on the electrophile IGRE AlCl 3 R AlBr 3 (d) (i) First reactant = H 3 ALLW a HCl R H HCl IGRE conditions/concentration Second reactant = ALLW correct structural R displayed R skeletal formulae R a combination of above as long as unambiguous Third reactant = ALLW

9 (ii) FIRST CHECK THE ASWER THE ASWER LIE IF answer = 1.35 (g) award 3 marks IF answer = 0.54 (g) award 2 marks (no scale-up) IF answer = (g) award 2 marks (incorrect scale-up) n(compound D) = 1.73/346 = mol n(1,3-diaminobenzene) required = 100/40 x = mol Molar mass of 1,3-diaminobenzene = 108 (g mol 1 ) AD Mass of 1,3-diaminobenzene = (108)(0.0125) = 1.35 g 3 ATATE ASWER WITH TICKS AD CRSSES ETC If there is an alternative answer, check to see if there is any ECF credit possible ALLW ECF from incorrect amount, scale-up or molar mass Alternative 1 n(compound D) = 1.73/346 = mol Molar mass of 1,3-diaminobenzene = 108 (g mol 1 ) AD Mass of 1,3-diaminobenzene = ( )(108) = g Mass of 1,3-diaminobenzene required = (0.540)(100/40) = 1.35 g Alternative g gives 108 g 1.73 g gives 108/364 x 1.73 = 0.54 g 0.54/40 x100 = 1.35 g (iii) (compound D has) two chiral centres 3 ALLW (Compound D) has two asymmetric carbons R has two stereocentres Four optical isomers exist ALLW four enantiomers R two pairs of enantiomers (Synthesis could) use enzymes R bacteria R use (chemical) chiral synthesis R chiral catalysts R use natural chiral molecules R single isomers (as starting materials) IDEPEDET MARK ALLW biological catalysts ALLW chiral transition metal complex/catalyst R stereoselective transition metal complex/catalyst ALLW 'chiral pool'/chiral auxiliary Total 18

Question Answer Mark Guidance 1 (a) (i) M1 p-orbitals overlap (to form pi/π-bonds) 4 ANNOTATE ANSWER WITH TICKS AND CROSSES ETC

Question Answer Mark Guidance (a) (i) M p-orbitals overlap (to form pi/π-bonds) 4 ANNOTATE ANSWER WIT TICKS AND CROSSES ETC IGNORE p-orbitals overlap to form sigma bonds M2 π-bond(s) are delocalised in