Introduction to Organic Chemistry - Isomerism Mark schemes

Q1.(a)     (i)      M1 pentan-3-one only

1

M2 CH3CH2CH2COCH3

(insist on C=O being drawn out)(penalise use of C3H7)

1

(ii)     aldehyde         (CH3)2CHCH2CHO1

ketone             (CH3)2CHCOCH3

1

(insist on a clear structure for the C=O of the functional groups, but do not be too harsh on the vertical bonds between carbon atom son this occasion)(If both structures correct, but wrong way around, award one mark)(ignore names)

(b)     (i)      CH3CH2CH2CH2CHO + [O] → CH3CH2CH2CH2COOH(accept C4H9CHO going to C4H9COOH)(insist on a balanced equation – for example do not credit [O] over the arrow alone)

1

(ii)     pentanoic acid(credit pentan–1–oic acid)

1

(c)     (i)      CH3CH2CH2CH2CH2OH OR pentan–1–ol(If both a structure and a formula are given, credit either correct one of these provided the other is a good, if imperfect, attempt)

1

(ii)     Primary(credit 1o or 1)

1[8]

Q2.(a)     Electrophile: e– pair / lone pair acceptor or e– deficient species or e–

seeking species (1)For ‘species’ accept atom, molecule, ionNOT ‘+’ ionNOT ‘attracted to ‘- ’ charge’

          Addition: reaction which increases number of substituents orconvert double bond to single bond or where two moleculesform one molecule (1)

2

(b)     (High) e– dense or e– rich C=C or e– rich π bond or 4 e– between the C’s (1)NOT just ‘C=C’

          causes induced dipole in Br2 (1)Ignore refs to ‘temporary’can score M2 from δ+ / δ– on Br2 in (c) unless a contradicting error in (b)

2

(c)     Mechanism:

 If incorrect alkene, lose M3 (wrong cation)Mark M4 conseq on M3

 

          Name of product: 1,2-dibromopropane (1)5

(d)     addition (1)Not additional

1[10]

Q3.(a)     (base) elimination

(penalise other words before ‘elimination’ e.g. nucleophilic)1

M1: curly arrow from lone pair of electrons on oxygen of hydroxide ion(insist on a lone pair of electrons on the oxygen atom and a negative charge, but only credit this mark if the attack is to a correct H atom)

1

M2: curly arrow from the middle of the C-H bond to the middleof the C–C bond

1

(only credit this mark if the arrow originates from the correct C–H bond and if an attempt has been made at M1)

M3: curly arrow from the middle of the C–Br bond towards/alongsidethe Br atom

(credit M3 independently unless the bond breaking is contradicted by an additional arrow)(penalise curly arrow if the C–Br has a formal positive charge)(credit full marks for an E1 mechanism, with M2 awarded for a correct curly arrow on the correct carbocation)

(award a maximum of two marks for either an incorrect haloalkane or an incorrect organic product)(maximum 2 marks for use of 'sticks' for the haloalkane, unless RE from 2(b), when credit can be given)

(b)     (i)      M1: compounds with the same structural formula1

M2: but the bonds/groups/atoms have different spatialarrangements or orientation or configuration/are arrangeddifferently in space/3D

(ignore reference to the same molecular formula for M1)1

(ii)     M1: correct structural representation for cis-but-2-ene andits name or its identification as the cis isomer

1

M2: correct structural representation for trans-but-2-eneand its name or its identification as the trans isomer

(accept representations which are 90° to linear)(award one mark for two correct structures but either wrong/no names)(maximum 1 mark for an incorrect alkene)

1

(iii)     geometric(al) or cis-trans1

(c)     nucleophile or electron pair donor(penalise ‘base’)

1

(d)     CH3CH2CH2CH2Br + 2NH3 → CH3CH2CH2CH2NH2 + NH4Br(M1 correct product)(M2 balanced equation using 2NH3 and leading to NH4Br)(penalise M1 for use of C4H9NH2 or for incorrect haloalkane, but allow consequent correct balancing of equation with 2 moles of ammonia)

2

(1–)butylamine(credit 1–aminobutane and butyl–1–amine)(award QoL mark for correct spelling)

1[13]

Q4.(a)     Any two of these isomers

 1

(b)     Chain isomerismMark consequential to part (a)

1

(c)     C6H14 + 6.5O2 ⟶ 6CO + 7H2OM1 Product is CO or CM2 Balanced equation

1

OR

C6H14 + 3.5O2 6C + 7H2OAllow equations containing CO2 as long as either C, CO or both are also present

1

(d)     Less energy given out by the fuel / engine is less powerful / less efficient / needsto burn more fuel to get the same energy / increased costs due to need to usemore fuel

Do not allow answers linked to CO poisoning or incomplete combustion

1[5]

Q5.(i)

Isomer Name  

CH3CH2CH2CH2OH butan-1-ol  

 

2-methylpropan-2-ol  

 

(2-)methyl propan-1-ol  (1)

NOT prop-1-ol

 

butan-2-ol  (1)OR 2-butanol

NOT but-2-olNOT hydroxyNo RE

Allow e in the names2

(ii)     Structural (1)OR chain and position(al)

3[3]

Q6.(a)     Structure of P:

 (1)

Structures of Q and R:

 Q and R in any order

3

(b)     (i)      Racemic mixture: equal mixture of optical isomers / enantiomersOR in explanation

         Explanation: planar (>C=O) (1)                    attack from either side is equally likely (1)

(ii)     Reagent S: HCN or (KCN / HCl or H2SO4) (1)

Compound T:  (1)

Compound U:  (1)6

[9]

Q7.1(-)bromobutane

1

          correct structure for 1-bromo-2-methylpropane(C–C bonds must be clear where drawn)

1[2]

Q8.

(a)     (i)      Molecule/compound/consists/composed/made up of hydrogen andcarbon only (1)

(ii)     CnH2n+2 (1)

(iii)     C6H14 only (1)Do not credit structures alone or in addition.

3

(b)     Chemically similar / react in same way / same chemistryDiffer by CH2

gradation in physical properties OR specified trend e.g. b.p.same functional group

Any 2, 2 marks 1 + 1Not same molecular formula

2

(c)     (i)      Same molecular formula (1)NOT same Mr

different structural formula / structures (1) (or atoms arranged in different way)

NOT different spatial arrangementsOnly credit M2 if M1 correct

(ii)     2-methylpentane (1)2,2-dimethylbutane (1)

(iii)    

 OR correct condensed / structural formulaPenalise “sticks” oncePenalise absence of vertical bonds oncepenalise badly drawn bonds once (vertical between H atoms)

6

(d)     (i)      M1 % by mass of H = 7.7(0)% (1)M2          mol H = 7.70 / 1 = 7.70              mol C = 92.3 / 12 = 7.69 (1)

M3 (ratio 1:1 ) CH

Credit variations for M2 e.g. 78 ×  = 6

and  = 6Correct answer = 3 marks

(ii)     (CH has empirical mass of 13 and  = 6 ) C6H6 (1)

Correct answer 1 mark4

[15]

Q9.(a)     (i)      Prevents release of toxic CO

More energy efficient (releases more energy on combustion)1

(ii)     C6H14 + 6.5O2 → 6CO + 7H2O1

         Suitable product eg CO or C1

         Balanced equation1

(iii)     Detect CO gas or C (soot or particles) in exhaust gases1

(b)     CH3CH2CH2CH(CH3)2

1

          2-methylpentane1

          CH3CH2CH(CH3)CH2CH3 etc1

(c)     (i)      CH3CH2CH2CH=CH2

1

(ii)     Alumino silicate etc1

(iii)     Can be made into polymers (or alcohols etc)1

(d)     (i)      % atom economy = mass CH2Cl2/total massreactants = 85 × 100/158

1

= 53.8%1

(ii)     Because expensive chlorine is not incorperated intodesired product Raise money by selling HCl

1[14]

Q10.         (a)     A       any C5 alkene

1

B

 1

(b)     C

 

         or CH3COOH    or      HCOOCH3

1

          D

         or HOCH2CHO1

(c)     E

 1

          F

 1

(d)     G

 1

          H

 1

(e)     I

 1

          J

   NOT hex-3-ene1

[10]

Q11.(a)     (i)      fractional distillation or fractionation

1

(ii)     C9H20 only1

(iii)     C11H24 + 17O2 → 11CO2 + 12H2O1

(iv)    C11H24 + 6O2 → 11C + 12H2O1

(b)     (i)     C10H22 → C3H6  + C7H16

1

(ii)     correctly drawn structure of methylpropene(insist on clearly drawn C-C and C=C bonds)

1

(c)     Any two from

o     chemically similar or chemically the same or react inthe same way

o     same functional group

o     same general formula

o     differ by CH2

(penalise same molecular formula or same empirical formula)

2[8]

Q12.(a)     M1 curly arrow from lone pair on oxygen of hydroxide ion to

H atom on C-H adjacent to C-Br1

M2 curly arrow from single bond of adjacent C-Hto adjacent single bond C-C

(only credit M2 if M1 is being attempted to correct H atom)1

M3 curly arrow from C-Br bond to side of Br atom

(credit M3 independently)1

(b)     Ml credit a correct structure for either geometrical E-Z isomer and itsdesignation as either cis or trans.OR credit two correct geometrical E-Z isomer structures(ignore the names)OR credit two correct names for cis pent-2-ene and transpent-2-ene (ignore the structures)

1

M2 credit a second mark if all four parts of the required structures andnames are correct.

(credit “linear” structures)(insist on the alkyl groups being attached clearly by C-C bonds)

1

(c)     (i)      Ml curly arrow from middle of C = C bond to H atom on H-Br(penalise M1 if partial negative charge or formal positive charge on H)(penalise Ml if pent-2-ene is used)

1

         M2 curly arrow from H-Br bond to side of Br atom1

M3 correct structure for correct secondary carbocation1

M4 curly arrow from lone pair on bromide ion to the positivecarbon of carbocation, ensuring that bromide ion has anegative charge.

(with the exception of pent-2-ene, if the wrong alkene is used, only penalise the structure M3)(penalise the use of two dots in addition to a covalent bond, once only)

1

(ii)     1-bromopentane1

(iii)     Ml 2-bromopentane is formed via the secondary (or 2°)carbocation

1

OR 1-bromopentane is formed via the primary (or 1°)carbocationM2 a secondary carbocation is more stable than a primarycarbocation -award this mark only if the quality of language justifiesthe award.

(the argument must involve clear statements about carbocations)

1[12]

Q13.(a)     General formula;

          Chemically similar;

          Same functional group;

          Trend in physical properties eg inc bp as Mr increases;

          Contains an additional CH2 group;Any two points.

2 max

(b)     (i)

 All bonds and atoms must be shown.

1

         C3H6Cl;Allow any order of elements.Do not allow EF consequential on their wrong displayed formula.

1

(ii)     Same Molecular formula/ both C6H12Cl2/ same number and typeof atoms;

1

Different structural formula/ different structure/ differentdisplayed formula;

Not atoms or elements with same MFCE=O.Allow different C skeleton.If same chemical formula can allow M2 only.M2 insufficient to say atoms arranged differently.M2 consequential on M1.

1

(c)     Mr =228 for total reactants;1

           = 67.98%;Allow 67.98 or 68.0 or 68%.

1

(d)     (i)      Bp increases with increasing (molecular) size/ increasing Mr/increasing no of electrons/increasing chain length;

Atoms CE =0.1

Increased VDW forces (between molecules) (when largermolecule)/ bigger IMFs;

QWCNot dipole-dipole or hydrogen bonds.If VDW between atoms in M2 CE = 0.

1

(ii)     Fractional distillation/ fractionation/ GLC/chromatography;1

[11]

Q14.(a)     2-bromobutane;

1

(b)     Elimination;(penalise “nucleophilic” OR “electrophilic” before the word “elimination”)

1

M1: curly arrow from lone pair on oxygen of hydroxide ion to H atomon correct C-H adjacent to C-Br;

(penalise M1 if KOH shown as covalent with an arrow breaking the bond)

1

M2: curly arrow from single bond of adjacent C-H to adjacentsingle bond C-C;

(only credit M2 if M1 is being attempted to correct H atom)1

          M3: curly arrow from C-Br bond to side of Br atom;(credit M3 independently unless arrows contradict)(Credit possible repeat error from 2(c)(iii) for M3)(If the wrong haloalkane is used OR but-1-ene is produced, award MAX. 2 marks for the mechanism)(If E1 mechanism is used, give full credit in which M1 and M2 are for correct curly arrows on the correct carbocation)

(c)     (i)      (structural) isomers/hydrocarbons/compounds/they have the samemolecular formula, but different structural formulas/different structures;  1

(penalise statements which are not expressed in good English and which do not refer clearly to structural isomers i.e. plural)(penalise statements which refer to “different (spatial) arrangements”)(credit” different displayed formulas”)(Q of L mark)

(ii)     Correct structure for but-1-ene;1

[7]

Q15.(a)     Pentan-2-one

ONLY but ignore absence of hyphens1

(b)     Functional group (isomerism)Both words needed

1

(c)     (i)     

 Award credit provided it is obvious that the candidate is drawing the Z / cis isomerThe group needs to be CHOHCH3 but do not penalise poor C–C bonds or absence of brackets around OHTrigonal planar structure not essential

1

(ii)     Restricted rotation (about the C=C)

OR

No (free) rotation (about the C=C)1

(d)    

M1 Tollens’ (reagent)

(Credit ammoniacal silver nitrate OR a description of making

Tollens’)

(Do not credit Ag+, AgNO3 or [Ag(NH3)2

+] or “the silver mirror test” on their own, but

mark M2 and M3)

M1 Fehling’s (solution) / Benedict’s

(Penalise Cu2+(aq) or CuSO4 but mark M2 and M3)

M2 silver mirror

OR black solid or black precipitate

M2 Red solid/precipitate

(Credit orange or brown solid)

M3 (stays) colourless

OR

no (observed) change / no reaction

M3 (stays) blue

OR

no (observed) change / no reaction

 If M1 is blank CE = 0, for the clipCheck the partial reagents listed and if M1 has a totally incorrect reagent, CE = 0 for the clipAllow the following alternativesM1 (acidified) potassium dichromate(VI) (solution); mark on from incomplete formulae or incorrect oxidation stateM2 (turns) greenM3 (stays) orange / no (observed) change / no reactionORM1 (acidified) potassium manganate(VII) (solution);mark on from incomplete formulae or incorrect oxidation stateM2 (turns) colourlessM3 (stays) purple / no (observed) change / no reactionIn all cases for M3

Ignore “nothing (happens)”Ignore “no observation”

3

(e)     (i)      Spectrum is for Isomer 1

or named or correctly identifiedThe explanation marks in (e)(ii) depend on correctly identifying Isomer 1.The identification should be unambiguous but candidates should not be penalised for an imperfect or incomplete name. They may say “the alcohol” or the “alkene” or the “E isomer”

1

(ii)     If Isomer 1 is correctly identified, award any two from

•        (Strong / broad) absorption / peak in the range3230 to 3550 cm–1 or specified value in this rangeor marked correctly on spectrumand(characteristic absorption / peak for) OH group /alcohol group

•        No absorption / peak in range 1680 to 1750 cm–1 orabsence marked correctly on spectrumand(No absorption / peak for a) C=O group / carbonyl group / carbon-oxygen double bond

•        Absorption / peak in the range 1620 to 1680 cm–1

or specified value in this range or marked correctlyon spectrumand

          (characteristic absorption / peak for) C=C group/ alkene / carbon-carbon double bondIf 6(e)(i) is incorrect or blank, CE=0Allow the words “dip” OR “spike” OR “trough” OR “low transmittance” as alternatives for absorption.Ignore reference to other absorptions e.g. C-H, C-O

2[10]

Q16.(a)     M1:    CH3CH2CH2CH2OH;

1

M2:    CH3CH(OH)CH2CH3;(penalise incorrect alcohols in part (a), but mark consequentially in part (b) and in part (c), if relevant)(if three alcohols drawn, award MAX. 1 mark)

1

(b)     M1, M2 and M3:   Correct structures for butanal, butanoneand butanoic acid;

(award these structure marks wherever the structures appear, but insist that the C=O is shown in each structure

and additionally, the C-O in the carboxylic acid3

M4:                       balanced equation for the reaction of butan-1-olwith [O] to produce butanal and water;

1

M5:                       balanced equation for the reaction of butan-1-olwith [O] to produce butanoic acid and water

OR

balanced equation for the reaction of butanal with [O] toproduce butanoic acid;

1

M6: balanced equation for the reaction of butan-2-ol with [O] toproduce butanone and water;

(Credit condensed structures or molecular formulas in each equation, provided it is obvious to which reaction the equation refers) (Insist that whatever formula is used in each equation that it is a conventional representation of the compound; for example penalise CH3CH2CH2COH for butanal)

1

(c)     M1:    Correct structure for 2-methylpropan-2-ol;M2:    2-methylpropan-2-ol

1

OR

methylpropan-2-ol;(penalise on every occasion in parts (a) and (c), structures for the alcohols that are presented with the alcohol functional group as C-H-O)

1[10]

Q17.(a)     (Different) boiling points

Ignore mp’s, references to imf, different volatilities1

(b)     (i)      Compound which have the same molecular formulaAccept same no and type of atom for M1But If same (chemical) formula M1 = 0 but allow M2If empirical formula CE = 0/2

1

but different structures/different structuralformulae/different displayed formulae

M2 dependent on M11

(ii)     3-methylbut-1-eneonlyignore commas and hyphens

1

(iii)    

 Allow any correct structure with a cyclic alkane

1

Do not allow

 i.e with an H missing on one C

(c)     C13H28

only1

Making plastics/used to make polymers or polythene/usedto make antifreeze/make ethanol/ripening fruit/any namedadditional polymer

not used as a plastic/polymer/antifreezenot just ‘polymers’ – we need to see that they are being made

1[6]

Q18.(a)     •        (Same) General formula/allow a named homologous series

with its general formula

•        Chemically similar/same (chemical) reactions

•        Same functional group

•        Trend in physical properties/eg inc bp as Mr increases

•        (Molecules) increase by CH2/Mr = 14Any two points

2

(b)     Fractional distillation/fractionation/chromatographyAllow GLC

1

(c)     (Molecules/compounds/substances) with the same molecularformula/same number and type of atoms

Allow alkanes with same molecular formulaAllow same chemical formula in M1 = 0 but can allow M2

1

but different structural formula/different displayed formula/differentarrangement of atoms/different structures

Not different positions in space1

2,4-dimethylhexaneM2 dependent on M1

1

C4H9

Ignore the absence of dash and/or commas1

(d)     less surface contact/less surface area/less polarisablemolecule

1

so fewer/weaker/less Van der Waals’/vdw forcesAllow more spherical or fewer points of contactNot smaller molecule/not more compact molecule/not shorter chainAllow converse argumentsMust be comparative answer ie not just few VDW forcesQoLAssume ‘it’ refers to the branched isomer

1[9]

Q19.(a)     Cn H2n+2

Allow x in place of n1

(b)    

 

ChainMust show every bondAllow branched chain

2

(c)     C9H20

Only1

To break the (C-C and/or C-H) bondsM2=0 if break C=C

1

To make products which are in greater demand / highervalue / make alkenes

Not more useful productsAllow specific answers relating to question

1

(d)     C5H12 + 3O2 → 5C + 6H2OAllow other balanced equations which give C and CO/CO2

1

Causes global dimming / exacerbates asthma / causesbreathing problems / makes visibility poor / smog

Apply list principleIgnore causes cancer / toxic

1

(e)      (x 100)1

74.48%Allow 74.5%

1

3Only

1

(f)      2,3-dichloro-3-methylpentaneIgnore punctuation

1

C3H6Cl

Only1

[13]

Q20.(a)      (i)     CnH2n / CxH2x

1

(ii)     Fractional distillation / GLC / gas liquid chromatography / fractionationDo not allow cracking / distillation

1

(b)     (i)     But-1-ene / but1eneIgnore hyphens and commasDo not allow butene-1 / but-2-ene / butane / butane /alkene / C4H8 / propene / straight-chain alkene

1

(ii)     A structure of cyclobutane ormethyl-cyclopropane

Allow skeletal formula.1

(c)     (i)     C15H32 → 2C4H8 + C7H16

Do not accept multiples.1

(ii)     Thermal crackingNot catalytic cracking or cracking.

1

To produce products that are in greater demand / more valuable / moreexpensive / more profitable

The (unsaturated) alkene or the (unsaturated) molecule or X produced can be polymerised or can be made into plastics.Ignore more useful products.

1

(iii)     Break (C–C or C–H) bondsAllow to overcome the activation energy.Allow to break the carbon chain.Penalise breaking wrong bonds.

1

(d)     (i)     H2

Only.1

(ii)     Fuel / LPGAllow camping gas, lighter fuel, propellant, refrigerant, cordless appliances.Do not allow petrol or motor fuel.Ignore natural gas.

1

(iii)     C4H10 + 2.5O2 → 4C + 5H2OAccept multiples.

1

(iv)     SO2 / sulfur dioxideIf other sulfur oxides, mark on.

1

Calcium oxide / CaO / lime / quicklimeAllow CaCO3 / allow Ca(OH)2 or names.Allow any solid base.M2 dependent on M1.Do not allow limewater.

1

(v)     NeutralisationAllow acid-base reaction.Allow flue gas desulfurisation / FGD

1

(e)    (Molecules) are similar sizes / have similar Mr / have similar number of electronsChemical error CE = 0/2 if breaking bonds.Allow similar number of carbon and hydrogen atoms / similar surface area / similar chain length.Can accept same number of carbon atoms.Do not accept same number of H atoms / same number of bonds.Ignore similar amount of bonds.

1

Similar van der Waals forces between molecules / similar intermolecular forces(IMF)

Not similar incorrect IMF eg dipole-dipole1

[16]

Q21.(a)     X (O–H) (alcohols)

penalise acid or missing “alcohol”1

Y C=Oallow carbonyl

1

 NOT acid

4

(b)    

 

Allow conseq dibromocompounds following incorrect unbranched alkenes NOT allow dibromocompound consequent on a duplicate alkeneNOT allow monobromocompounds if HBr added

3

 3

6:3:1 either next to correct structure or to none1

Allow a mark for identifying correct dibromocompound with three peakseven if integration ratio is wrong

1

if 6:3:1 missing or wrong, no marks for splitting

Only award a mark for splitting if it is clear which integration number itrefers to

6 singlet or drawn1

3 doublet or drawn1

1 quartet/quadruplet or drawn1

(max 10 marks)[16]

Q22.(a)     (i)     Crude oil / oil / petroleum

Do not allow ‘petrol’1

(ii)     Fractional distillation / fractionation / fractionatingNot distillation alone

1

(b)     (i)     5Allow five / V

1

(ii)     Chain (isomerism)Allow branched chain / chain branched / side chain (isomerism)Ignore position (isomerism)Do not allow straight chain / geometric / branched / function

1

(c)     (i)     C12H26 / H26C12

Only1

(ii)     Thermal crackingIf not thermal cracking, CE = 0/2If blank mark on

1

High temperatureAllow ‘high heat’ for ‘high temperature’

(400°C < T < 900°C) or (650 K < T < 1200 K)Not ‘heat’ aloneIf no T, units must be 650 – 900

and

High pressure (> 10 atm, > 1 MPa, >1000 kPa)1

(iii)    To produce substances which are (more) in demand / produce products with ahigh value / products worth more

Ignore ‘to make more useful substances’1

(d)     (i)     Corrosive or diagram to show this hazard symbolIgnore irritant, acidic, toxic, harmful

1

(ii)     (  120.5       × 100)(86 + 71             )

=76.75(%) or 76.8(%)Allow answers > 3 sig figs

1

(e)     2,2-dichloro-3–methylpentaneIgnore punctuationAny order

1

C3H6Cl1

[12]

Q23.(a)     (Compounds with the) same molecular formula but different structural / displayed /

skeletal formula1

(b)     (basic) elimination1

Mechanism points:

Correct arrow from lone pair on :OH– to H on C adjacent to C–Br1

Correct arrow from C–H bond to C–C1

Correct arrow from C–Br bond to Br1

Structure of chosen product1

 

OR

 [6]

Q24.(a)     (i)      M1 (Compounds / molecules with) the same structural formula

Penalise M1 if ‘same structure’ or ‘different structural / displayed formula’.

M2 with atoms / bonds / groups arranged differently in space

OR atoms / bonds / groups with different spatial arrangements / different orientation

Ignore references to ‘same molecular formula’ or ‘same empirical formula’.Mark independently.

2

(ii)     

Credit C–H3CCredit C2H5

Penalise C–CH3CH2

1

(b)     M1 Br2 OR bromine (water) OR bromine (in CCl4 / organic solvent)If M1, has no reagent or an incorrect reagent, CE=0.Ignore ‘acidified’.

M2    Isomer 1: decolourised / goes colourless / loses its colourFor M1 penalise Br (or incorrect formula of other correct reagent), but mark on.

M3  Isomer 2: remains orange / red / yellow / brown / the same OR no reaction / no (observable) change OR reference to colour going to the cyclopentane layer

For M1, it must be a whole reagent and / or correct formula.If oxidation state given in name, it must be correct. If ‘manganate’ OR ‘manganate(IV)’ or incorrect formula, penalise M1, but mark on.

Alternatives : potassium manganate(VII)

M1 KMnO4 in acid M2 colourless M3 purple

M1 KMnO4 in alkali / neutral M2 brown solid M3 purple

Credit for the use of iodine

M1 iodine (solution / in KI) M2 colourless M3 (brown) to purple (credit no change)

Credit for the use of concentrated H2SO4

M1 concentrated H2SO4 M2 brown M3 no change / colourlessIgnore ‘goes clear’.Ignore ‘nothing (happens)’.Ignore ‘no observation’.No credit for combustion observations.

3

(c)    (i)      (Both infrared spectra show an absorption in range) 1620 to 1680 (cm−1)Ignore reference to other ranges (eg for C–H or C–C).

1

(ii)     The fingerprint (region) / below 1500 cm−1 will be different or its fingerprinting will be different

OR

different absorptions / peaks are seen (in the region) below 1500 cm−1 (or a specified region within the fingerprint range)

Allow the words ‘dip’ OR ‘spike’ OR ‘low transmittance’ as alternatives for absorption.QoL

1

(d)     

All bonds must be drawn.Ignore bond angles.

1

(e)    (i)      M1    Electrophilic addition

M1 both words needed.

Penalise one mark from their total if half-headed arrows are used.

M2 must show an arrow from the double bond towards the H atom of the H–Br molecule

M2 Ignore partial negative charge on the double bond.

M3 must show the breaking of the H–Br bondM3 Penalise incorrect partial charges on H–Br bond and penalise formal charges.

M4 is for the structure of the tertiary carbocationPenalise M4 if there is a bond drawn to the positive charge.Penalise once only in any part of the mechanism for a line and two dots to show a bond.

M5 must show an arrow from the lone pair of electrons on the negatively charged bromide ion towards the positively charged carbon atom of either a secondary or a tertiary carbocation

For M5, credit attack on a partially positively charged carbocation structure but penalise M4.Max 3 of any 4 marks in the mechanism for wrong organic reactant or wrong organic product (if shown) or secondary carbocation.Max 2 of any 4 marks in the mechanism for use of bromine.Do not penalise the correct use of 'sticks”.

NB The arrows here are double-headed5

(ii)     M1 Reaction goes via intermediate carbocations / carbonium ionsM1 is a lower demand mark for knowledge that carbocations are involved.

M2 (scores both marks and depends on M1)

Tertiary carbocation / carbonium ion is more stable (than the secondary carbocation / carbonium ion)

OR

Secondary carbocation / carbonium ion is less stable (than the tertiary carbocation / carbonium ion)

M2 is of higher demand and requires the idea that the secondary carbocation is less stable or the tertiary carbocation is more stable. Reference to incorrect chemistry

is penalised.A carbocation may be defined in terms of alkyl groups / number of carbon atoms, rather than formally stated.

2

(f)     M1 EliminationM1 credit ‘base elimination’ but no other qualifying prefix.

Penalise one mark from their total if half-headed arrows are used.

M2 must show an arrow from the lone pair on oxygen of a negatively charged hydroxide ion to a correct H atom

Penalise M2 if covalent KOH

M3 must show an arrow from a correct C–H bond adjacent to the C–Br bond to a correct C–C bond. Only award if an arrow is shown attacking the H atom of a correct adjacent C–H bond (in M2)

M4 is independent provided it is from their original molecule BUT penalise M2, M3 and M4 if nucleophilic substitution shown

Award full marks for an E1 mechanism in which M2 is on the correct carbocation

NB The arrows here are double-headedPenalise M4 for formal charge on C or Br of the C–Br bond or incorrect partial charges on C–Br.Penalise M4 if an additional arrow is drawn from the Br of the C–Br bond to, for example, K+.Ignore other partial charges.Penalise once only in any part of the mechanism for a line and two dots to show a bond.Max 2 of any 3 marks in the mechanism for wrong reactant or wrong organic product (if shown) or a correct mechanism that leads to the alkene 2-methylbut-2-ene.Credit the correct use of “sticks” for the molecule except for the C–H being attacked.

M5 hydroxide ion behaves as a base / proton acceptor / electron pair donor / lone pair donor

Penalise M5 if ‘nucleophile’.5

[21]

Q25.(a)     (i)      (Compounds with the) same molecular formula

Allow same number and type of atom for M1Ignore same general formula.

1

But different structural formula / different displayed formula / different structures / different skeletal formula

M2 dependent on M1Not different positions of atoms / bonds in space.

1

(ii)     But-2-eneAllow but-2-ene.Allow but 2 ene.Ignore punctuation.

1

(iii)    (2)-methylprop-(1)-eneDo not allow 2-methyleprop-1-ene.

1

(iv)    

 Do not allow skeletal formulae.Penalise missing H and missing C

1

(b)     (i)      C4H8 + 2O2 → 4C + 4H2OAccept multiples.

1

(ii)     Exacerbates asthma / breathing problems / damages lungs / smog / smoke / global dimming

Ignore toxic / pollutant / soot / carcinogen.Do not allow greenhouse effect / global warming / acid rain / ozone.

1

(c)     (i)      C16H34

Allow H34C16

C and H must be upper case.1

(ii)      Jet fuel / diesel / (motor) fuel / lubricant / petrochemicals / kerosene / paraffin / central heating fuel / fuel oil

Ignore oil alone.Not petrol / bitumen / wax / LPG / camping fuel.

1

(d)     (i)       C8H18 + 25NO → 8CO2 + 12.5 N2 + 9H2OAccept multiples.

1

(ii)      Ir / iridium

OR

Pt / platinum

OR

Pd / palladium

OR

Rh / rhodium1

[11]

Q26.(a)     Saturated − single bonds only / no double bonds

1

Hydrocarbon − contains carbon and hydrogen (atoms) only1

(b)     C16H34 + 16.5O2 16CO + 17H2OAllow multiples

1

(c)     (On combustion) SO2 producedAllow equation to produce SO2. Ignore sulfur oxides.

1

Which causes acid rainIf formula shown it must be correctM2 is dependent on M1. But if M1 is sulfur oxides, allow M2.For M2 allow consequence of acid rain or SO2.

Ignore greenhouse effect and toxic1

(d)     (i)      C16H34 C8H18 + C2H4 + 2C3H6

Allow multiples1

(ii)     polypropene / propan(-1 or 2-)ol / propane(-1,2-)diol / isopropanol / propanone / propanal

Accept alternative namesIgnore plastic and polymer

1

(iii)    

 1

(e)     

 Allow any unambiguous representation

1

(f)     2,4-dichloro-2,4-dimethylhexaneOnly but ignore punctuation

1[10]

Q27.(a)    

1

(b)     1

(c)     Stage 1: consider the groups joined to right hand carbon of the C=C bondExtended responseMaximum of 5 marks for answers which do not show a sustained line of reasoning which is coherent, relevant, substantiated and logically structured.

Consider the atomic number of the atoms attachedM1 can be scored in stage 1 or stage 2

1

C has a higher atomic number than H, so CH2OH takes priority1

Stage 2: consider the groups joined to LH carbon of the C=C bond

Both groups contain C atoms, so consider atoms one bond further away1

C, (H and H) from ethyl group has higher atomic number than H, (H and H) from methyl group, so ethyl takes priority

1

Stage 3: conclusion

The highest priority groups, ethyl and CH2OH are on same side of the C=C bond so the isomer is Z

Allow M5 for correct ECF conclusion using either or both wrong priorities deduced in stages 1 and 2

1

The rest of the IUPAC name is 3-methylpent-2-en-1-ol1

(d)     Moles of maleic acid = 10.0 / 116.0 = 8.62 × 10–2

AND mass of organic product expected = (8.62 × 10–2) × 98.0 = 8.45 g

Or moles of organic product formed = 6.53 / 98.0 = 6.66 × 10–2

1

% yield = 100 × 6.53 / 8.45

OR       = 100 × (6.66 × 10–2) / (8.62 × 10–2)

             = 77.294 = 77.3%

AND statement that the student was NOT correct1

[10]

Q28.(a)     (i)      (nucleophilic) addition-elimination

Not electrophilic addition-eliminationIgnore esterification

1

M3 for structure•                If wrong nucleophile used or O–H broken in first step, can                  only score M2.•               M2 not allowed independent of M1, but allow M1 for correct                  attack on C+•              + rather than δ+ on C=O loses M2.•                If Cl lost with C=O breaking lose M2.•               M3 for correct structure with charges but lone pair on O is                  part of M4.•               Only allow M4 after correct / very close M3.•                Ignore HCl shown as a product.

4

a    20-50 (ppm)    or single value or range entirely within this rangeIf values not specified as a or b then assume first is a.

1

b    50-90 (ppm)    or single value or range entirely within this range1

(ii)     

 Must have trailing bonds, but ignore n.

1

OR     –OCH2CH2CH2CH2CO–    OR     –CH2CH2CH2CH2COO–Allow

 but not        - C4H8−

one unit only

Condensation1

(b)      

  Tollens’ Fehling’s / Benedicts Acidified potassium dichromate

Penalise wrong formula for Tollens or missing acid with potassium dichromate but mark on.

1 

J No reaction / no(visible) change /no silver mirror

No reaction / no(visible) change /stays blue / no redppt

No reaction / no(visible) change / staysorange / does not turngreen

Ignore ‘clear’, ‘nothing’.Penalise wrong starting colour for dichromate.

1 

K Silver mirror /grey ppt

Red ppt

(allow brick red orred-orange)

(orange) turns green

1

J        Two (peaks)Allow trough, peak, spike.

1

K        Four (peaks)Ignore details of splitting.If values not specified as J or K then assume first is J.

1

(c)     If all the structures are unlabelled, assume that the first drawn ester is L, the second ester is M; the first drawn acid is N, the second P. The cyclic compound should be obvious.

Lester

                                     OR    H2C=C(CH3)COOCH3

All C5H8O2 L to P must have C=C.Allow CH3−.Allow -CO2CH3 etc.Allow CH2C(CH3)COOCH3.

1

Mester

                    CH3CH=CHCOOCH3    CH3CH=CHOOCCH3    CH3CH=C(CH3)OOCH 

                                 CH3CH=CHCH2OOCH         CH3CH2CH=CHOOCH

Allow either E–Z isomer.Allow CH3− or C2H5− but not CH2CH3−.

Allow CH3CHCHCOOCH3 etc.1

Nacid            

           (CH3)2C=CHCOOH       H2C=C(CH3)CH2COOH       H2C=C(COOH)CH2CH3

Allow CH3− or C2H5− but not CH2CH3−.

Allow −CO2H.Not cyclic isomers.Not the optically active isomer.

Allow (CH3)2CCHCOOH etc.

1

Pacid

            Allow −CO2H.

            CH3CH(COOH)CH=CH2

Allow      CH3CH(CO2H)CHCH2 or           CH3CH(CO2H)C2H3.

1

Q

          

Not cyclic esters.1

[19]

Q29.(a)     Alkenes

1

 Correctly drawn molecule of cyclobutane or methyl cyclopropane, need not be displayed formula

1

(b)     C6H14 (or correct alkane structure with 6 carbons)Allow hexane or any other correctly named alkane with 6 carbons

1

(c)     Poly(but-2-ene)1

(d)     High pressureAllow pressure ࣙ MPaMention of catalyst loses the mark

1

(e)     This question is marked using levels of response. Refer to the Mark Scheme Instructions for Examiners for guidance on how to mark this question.

Level 3

All stages are covered and the explanation of each stage is generally correct and virtually complete.

Answer communicates the whole process coherently and shows a logical progression from stage 1 and stage 2 (in either order) to stage 3.

5–6 marks

Level 2

All stages are covered but the explanation of each stage may be incomplete or may contain inaccuracies OR two stages are covered and the explanations are generally correct and virtually complete.

Answer is mainly coherent and shows progression. Some steps in each stage may be out of order and incomplete.

3–4 marks

Level 1

Two stages are covered but the explanation of each stage may be incomplete or may contain inaccuracies, OR only one stage is covered but the explanation is generally correct and virtually complete.

Answer includes isolated statements but these are not presented in a logical order or show confused reasoning.

1–2 marks

Level 0

Insufficient correct chemistry to gain a mark.0 marks

Indicative chemistry contentStage 1: consider effect of higher temperature on yield(Or vice versa for lower temperature)•         Le Chatelier’s principle predicts that equilibrium shifts to oppose any increase in temperature•         Exothermic reaction, so equilibrium shifts in endothermic            direction / to the left•         So a Higher T will reduce yieldStage 2: consider effect of higher temperature on rate(Or vice versa for lower temperature)•         At higher temperature, more high energy molecules•         more collisions have E>Ea•        So rate of reaction increases / time to reach equilibrium decreasesStage 3: conclusionIndustrial conditions chosen to achieve (cost-effective) balance of suitable yield at reasonable rate

[11]

Q30.(a)     NaOH/KOH

IGNORE OH-NOT M1 if any mention of acidified/H+ in reagents or

conditions1

Reaction 1 = ethanolic/alcoholic AND reaction 2 = aqueousIGNORE tempNOT ethanoic

1

rxn 1 = base/proton acceptor1

rxn 2 = nucleophile/lone pair donor/electron pair donor1

(Base) EliminationNOT nucleophilic

1

 

M6 must show an arrow from the lone pair on the oxygen of a negatively charged hydroxide ion to a correct H atom

M7 must show an arrow from a correct C–H bond on C adjacent to the C of the C–Br bond to a correct C–C bond. Only award if an arrow is shown attacking the H atom of a correct adjacent C–H bond in M6

M8 is independent provided it is from their original molecule and shows curly arrow from C-Br to Br

ALLOW correct E1 mechanismIGNORE incorrect inorganic productsIf forming pent-2-ene can award M8 only even if arrows in mechanism correctIf C chain length or halogen wrong in reactant or product max 2/3

111

(b)      1

 1

 1

If no M2 and M3 ALLOW 1 mark if both structures OR both names correctNOT cis and trans

No free rotation around C=CALLOW no rotation of C=C

1

2 different atoms/groups on each of the C=C Cs owtteIGNORE ‘functional’

1

(c)      Same volume/amount of AgNO3(aq) added to same volume/amount/no. of drops of haloalkane (in beaker/flask) in each experiment

Both volume references neededIGNORE inappropriate volumes

1

Same temp OR same [AgNO3] each time1

record time to measure sensible observation about the amount of AgCl ppt

e.g. first appearance of ppt / ppt obscures mark / reading on a colorimeterIGNORE colour of pptALLOW silver mirrorNOT reference to same time if describing method based on timing how long (for ppt to form)ALLOW gravimetric method based on same time for each experiment

1

Rate = amount/time OR proportional to 1/time OR reference to shorter time = higher rate/longer time = lower rate

ALLOW greater mass = higher rate if gravimetric method1

[17]

Q31.(a)    Crude oil OR petroleum

Not petrol.1

Fractional distillation / fractionationNot distillation alone.

1

(b)     C12H26 + 12.5O2 12CO + 13H2OAllow balanced equations that produce CO2 in addition to CO.Accept multiples.

1

(c)    (i)      M1 Nitrogen and oxygen (from air) react / combine / allow a correct equation

If nitrogen from petrol / paraffin / impurities CE = 0 / 2.1

M2 at high temperaturesAllow temperatures above 1000 °C or spark.Not just heat or hot.M2 dependent on M1.But allow 1 mark for nitrogen and oxygen together at high temperatures.

1

(ii)     2NO + O2 2NO2

Allow multiples.1

(iii)    4NO2 + 2H2O + O2 4HNO3

Allow multiples.1

(d)    (i)      CnH2n+2

Allow CxH2x+2

CnH2n+2Allow CxH2x+2

1

(ii)     C12H26 C6H14 + C6H12

Only.1

C3H7

Only.1

Zeolite / aluminosilicate(s)Ignore aluminium oxide.

1

(iii)    Larger molecule / longer carbon chain / more electrons / larger surface area

1

More / stronger van der Waals’ forces between moleculesAllow dispersion forces / London forces / temporary induced dipole-dipole forces between molecules.If breaking bonds, CE = 0 / 2.

1

(e)     2,2,3,3,4,4-hexamethylhexaneOnly.

Ignore punctuation.1

ChainIgnore branch(ed).

1

(f)     Cl2Only.

Cl–ClNot CL2 or Cl2 or CL2 or Cl2 or CL2.Ignore Chlorine.

1[16]

Q32.(a)     (i)     Alkane(s)

Ignore CnH2n+2

1

(ii)     C8H18 + 12.5O2 → 8CO2 + 9H2OAllow multiples

1

(iii)     2, 2, 4-trimethylpentane1

(b)     (i)      But-1-eneIgnore (E or Z)

1

(ii)     C14H30

1

(iii)     ThermalIf catalytic CE = 0

1

High pressure / 7000kPa / 70 atmsandHigh temperature/temperature in range 400-1000°C (673–1273K)

(Allow ≥1000 kPa or ≥10 atms – no upper value)Allow high temperature and pressure or high pressure and temperatureIf no units for temperature allow 673-1000Must show unambiguous structurePenalise lack of displayed formula once only

1

(iv)      1

 1

 1

[10]

Q33.(a)     2,2,4-trimethylpentane

1

(b)     51

(c)     C20H42   C8H18 + 2C3H6 + 3C2H4

1

(d)     Mainly alkenes formed1

(e)     4 (monochloro isomers)1

 1

(f)     

 1

(g)     C8H1735Cl = 96.0 + 17.0 + 35.0 = 148.0

and C8H1737Cl = 96.0 + 17.0 + 37.0 = 150.0

Both required1

Mr of this C8H17Cl   = 148.81

(h)         = 2.05 : 2.56 : 2.05

Simplest ratio =  

=                            1 : 1.25 : 11

Whole number ratio (× 4) = 4 : 5 : 41

MF = C8H10Cl81

[12]

Q34.

(a)      Must show all 4 groups bonded to C=CAllow CH3− for methyl group; allow C2H5 for ethyl groupAllow correct structure of the style

 Allow correct skeletal structure

 1

(b)     M1    electrophilic addition

 

NB the arrows here are double-headed1

M2    must show an arrow from the double bond towards the H atom of the H-Br molecule

1

M3    must show the breaking of the H-Br bond1

M4    is for the structure of the tertiary carbocation1

M5    must show an arrow from the lone pair of electrons on the negatively charged bromide ion towards the positively charged atom (of either a secondary or) of a tertiary carbocation

1

M6    3-bromo-3-methylpentane is formed from 3 y carbocation OR2-bromo-3-methylpentane is formed from 2 y carbocation

1

M7    3 y carbocation more stable than 2 y 1

M2-M5 Penalise one mark from their total if half-headed arrows are usedM2 Ignore partial negative charge on the double bondM3 Penalise incorrect partial charges on H-Br bond and penalise formal chargesPenalise M4 if there is a bond drawn to the positive chargePenalise only once in any part of the mechanism for a line and two dots to show a bondMax 3 of any 4 marks (M2-5) for wrong organic reactant or wrong organic product (if shown) or secondary carbocationMax 2 of any 4 marks in the mechanism for use of bromineDo not penalise the “correct” use of “sticks”For M5, credit attack on a partially positively charged carbocation structure but penalise M4M6 is high demand and must refer to product being formed from/via correct class of carbocationM7 is high demand and must be clear answer refers to stability of carbocations (intermediates) not productsCandidate that states that products are carbocations would lose M6 and M7M6,7 allow carbonium ion in place of carbocation; or a description of carbocation in terms of alkyl groups/ number of carbon atoms joined to a positive C

When asked to outline a mechanism, candidates are expected to draw a mechanism with curly arrows (specification 3.3.1.2). On this occasion only we would allow a detailed description as shown.M2 must describe the movement of a pair of electrons / curly arrow from the C=C towards the H atom of the H-Br molecule

M3 must describe the breaking of the H-Br bond with the bonding pair of electrons moving to the Br / curly arrow from H-Br bond to BrM4 is for the structure of the tertiary carbocation (i.e. positive C bonded to one methyl and two ethyl groups)M5 must describe the movement of a pair of electrons from the Br− ion to the positive C atom of the carbocation / curly arrow from the lone pair of electrons on the negatively charged bromide ion towards the positively charged C atom (of either a secondary or) of a tertiary carbocation

[8]