2.8 EXTRA QUESTIONS MS. (iii) C 6 H 5 CHCl 2 / C 6 H 5 CCl 3 / C 6 H 5 CHCHC 6 H 5 / other correct possible answer (1) 1

Transcription

1 .8 EXTRA QUESTIONS MS 1. (i) l l / ½ l l 1 (ii) l l 6 5 l l 6 5 l (iii) 6 5 l / 6 5 l / / other correct possible answer 1 [4]. (a) (i) (free)radical substitution 1 (both words required for the mark) (ii) uv light OR sunlight OR high temperature OR 150 o to 500 o 1 (iii) Propagation 1 (ignore chain, first, second in front of the word propagation) (iv) Termination 1 OR (penalise if radical dot is obviously on, but not otherwise) (penalise 5 ) (credit ) (ignore chain in front of the word termination) (b) (i) Fractional distillation OR fractionation 1 (credit gasliquid chromatography, GL) (ii) (credit 6 for ethane) [7]. (a) (i) (free) radical substitution 1 (both words required for the mark) initiation l l 1 (credit correct half arrows, but penalise double headed arrows) first propagation l l l l 1 second propagation l l l l 1 (penalise the absence of dots on radicals once only) (penalise radical dot on l of l once only) (ii) l l l l 1 (penalise if any radicals appear in this equation) Mill ill igh School 1

2 (b) M1: mol = 10.1/1.0 and mol l = 89.9/5.5 1 M: Ratio 0.84 :.5 OR 1: OR l 1 M: 7.0/Mr of l = 7.0/118.5 = Therefore l 6 1 (correct answer gains full credit) OR M1: /100 and /100 1 M: Ratio.9/1.0 : 1/5.5 OR : 6 1 M: l 6 1 (correct answer gains full credit) (c) any two from or 4 or 4 (or ) or 6 (or ) (ignore or ) (ignore equations and ignore names when given in addition to formulae) (penalise names alone) 4. (a) (i) substitution or hydrolysis nucleophile [10] (ii) O: O ( ) ( ) or ( ) ( ) O: 5 (b) (i) Type of reaction elimination Role of reagent base or proton acceptor Mill ill igh School

3 (ii) Structure of the alkene ( ) =( ) Mechanism ( ) ( ) :O or ( ) :O (iii) Structure of second alkene ( ) ( )= Name,4-dimethylpent--ene Structure of third alkene ( ) ( 5 )= Name -ethyl--methylbut-1-ene 10 [15] 5. (i) M1 curly arrow from lone pair of electrons on oxygen of hydroxide ion 1 (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 atom) M curly arrow from the middle of the bond to the middle of the bond. 1 (only credit this mark if the arrow originates from the correct bond and if an attempt has been made at M1) M curly arrow from the middle of the bond towards/alongside the atom. 1 (credit M independently unless the bond breaking is contradicted by an additional arrow) (penalise M curly arrow if the has a formal positive charge) (ignore partial charges on the bond, but penalise if incorrect) (credit full marks for an E1 mechanism, with M awarded for a correct curly arrow on the correct carbocation) (award a maximum of two marks for an incorrect haloalkane) (ignore products) Mill ill igh School

4 (ii) aloalkane/ 5 is made from ethane OR haloalkane is not (readily) available OR haloalkane is expensive OR it is (too) expensive/costly OR (reaction) yield is too low/poor OR it is too slow OR a valid reference to nucleophilic substitution/alcohol formation occurring as an alternative reaction. 1 (ignore references to temperature or to energy consumption) (do not credit statements which refer to the idea that this route is not chosen, because industry chooses another route e.g. cracking) 6. (i) M1: potassium cyanide OR KN OR sodium yanide OR NaN; 1 (ignore conditions - dissolved in (aq) or (alc) or KO(aq) all work) (penalise N) M: propanenitrile; 1 (credit propan-1-nitrile OR propan nitrile, but not propanitrile) (ii) M1: ammonia OR N ; 1 (If formula is written, insist that it is correct) (ignore conditions, but penalise acidic) M: ethylamine; 1 (credit aminoethane) [4] (iii) M1: curly arrow from lone pair on nitrogen of (correct formula for) ammonia towards/alongside atom of -; 1 (penalise M1 if formula of ammonia is wrong or has a negative charge or has no lone pair or arrow is from negative charge) M: curly arrow from - bond towards/alongside side atom; 1 (credit M independently) (penalise M if formal positive charge on atom of -) M: correct structure of the ethylammonium ion; 1 (credit the structure drawn out with all four bonds around the nitrogen atom OR written as 5 N OR N ) M4: curly arrow from the middle of one of the -N bonds towards the positive N atom; 1 (possible to credit M4 on an incorrect ethylammonium ion with no positive charge) (ignore use of ammonia or bromide ion etc. to remove proton from ethylammonium ion) (If the wrong haloalkane is used, award MAX. marks for the mechanism) (If S N 1 mechanism is used, give full credit in which M1 is for a curly arrow from the lone pair of the N atom of (correct formula for) ammonia towards/alongside the positive carbon atom of ) [8] Mill ill igh School 4

5 7. (a) or ( ) 1 (b) (i) or ( ) (ii) (nucleophilic) elimination :O or via ( ) 5 (c) methylbut1ene 1 [7] 8. (i) Mechanism: O: M1 l M redit M1 for O:.. l O M1 and M independent urly arrows must be from a bond or a lone pair Do not penalise sticks Penalise M1 if Na O precedes (penalise this once) Penalise incorrect δ δ for M Penalise on atom for M Only allow M1 for incorrect haloalkane Role of the hydroxide ion: nucleophile electron pair donor lone pair donor NOT nucleophilic substitution Mill ill igh School 5

6 (ii) Mechanism: O: M1 M.. l O l M O: Only allow M1 and M for incorrect haloalkane unless RE on (i) charge on on molecule, penalise M1 M independent M must be to correct M1 must be correct atom redit M1 and M via carbocation mechanism No marks after any attack of by O Role of the hydroxide ion: base 7 proton acceptor accepts [7] 9. (a) (i) Structure: O insist on O bond No credit for propan-1-ol even when named correctly redit propane--ol Name: propan--ol Not -hydroxypropane (ii) Name of mechanism: nucleophilic substitution (both words) (NOT S N 1 ors N ) Mechanism: M1 arrow (O) : O: arrow from (M) lone pair penalise incorrect polarity on - (M1) redit the arrows even if incorrect haloalkane If S N 1, both marks possible i.e. M1 M O correct carbocation : 5 Mill ill igh School 6

7 (b) (i) elimination (ii) base OR proton acceptor NOT nucleophile (base) [7] 10. (a) M1 NaO OR KO OR correct name 1 M aqueous or solution in water (ignore heat, reflux etc.) 1 (Penalise M1 for hydroxide ion alone, but mark on and credit M) (redit M ONLY for O as reagent and heat / warm / T=50 to 100 o ) (NaO(aq) scores M1 and M provided it is not contradicted) (Penalise M if NaO(aq) followed by concentrated or ethanol) (Penalise M1 and M if followed by acid) (b) Ethanolic OR alcoholic OR O / O solvent OR 1 aqueous ethanol/alcohol OR higher temperature (must be comparative) (Ignore heat or heat under reflux) (redit part (c) independently from part (b)) (Penalise ethanoic ) [] 11. (i) methylpropanenitrile (ii) Reagent KN onditions alcoholic/aq (iii) Name of mechanism nucleophilic substitution Mechanism [1] N N: [1] [1] : 7 [7] Mill ill igh School 7

8 1. (a) Name of mechanism: nucleophilic substitution Mechanism: :N δ δ (wrong dipole ( N N :N or loses mark) Marks S N 1 using same points M requires ( (M is for correct carbocation - if used wrong halogenoalkane lose M) :N 5 (b) Role of potassium hydroxide: Base Mechanism: :O Mark E1 using same points M/M :O 5 [10] 1. elimination 1 [1] 14. (i) N Not 4 9 N Pentanenitrile allow pentanonitrile, ignore numbers Mill ill igh School 8

9 (ii) Nucleophilic substitution M :N SN1 mechanism M1 M1 formation of carbocation including M attack by :N allow mechanism showing l If on lose M1 If KN shown lose M If δ c δ Bs lose M1 (iii) F bond is strong (er) Must imply F is stronger than bond ignore references to electronegativity, bond polarity etc. 6 [6] 15. (a) (base) elimination 1 (penalise other words before elimination e.g. nucleophilic) M1: curly arrow from lone pair of electrons on oxygen of hydroxide ion 1 (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 atom) 1 M: curly arrow from the middle of the - bond to the middle of the bond 1 (only credit this mark if the arrow originates from the correct bond and if an attempt has been made at M1) M: curly arrow from the middle of the bond towards/alongside the atom (credit M independently unless the bond breaking is contradicted by an additional arrow) (penalise curly arrow if the has a formal positive charge) (credit full marks for an E1 mechanism, with M 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 marks for use of.sticks. for the haloalkane, unless RE from (b), when credit can be given) (b) nucleophile or electron pair donor 1 (penalise base ) Mill ill igh School 9

10 (c) N N N 4 (M1 correct product) (M balanced equation using N and leading to N 4 ) (penalise M1 for use of 4 9 N or for incorrect haloalkane, but allow consequent correct balancing of equation with moles of ammonia) (1)butylamine 1 (credit 1aminobutane and butyl1amine) (award QoL mark for correct spelling) [8] 16. (i) potassium or sodium hydroxide (or other specific strong base) allow formula; not just hydroxide in ethanolic /alcoholic solution (independent of first mark) allow in ethanol, not just ethanol / with ethanol ignore references to heat / pressure (ii) KO K O structure of cyclohexene showing double bond minimum structure needed is a ring with units implied and double bond: do not allow KO over arrow equation correct overall ie balanced allow ionic equation (iii) elimination / dehydrohalogenation 1 ignore nucleophilic / electrophilic etc. [5] 17. (a) (i) KN N K 1 allow 7 allow 4 7 N (ii) nucleophilic substitution / SN 1 (b) N or N lone pair of electrons on atom [4] Mill ill igh School 10

11 18. (a) -bromobutane; 1 (b) Elimination; 1 (penalise nucleophilic OR electrophilic before the word elimination ) M1: curly arrow from lone pair on oxygen of hydroxide ion to atom on correct - adjacent to -; 1 (penalise M1 if KO shown as covalent with an arrow breaking the bond) M: curly arrow from single bond of adjacent - to adjacent single bond -; 1 (only credit M if M1 is being attempted to correct atom) M: curly arrow from - bond to side of atom; 1 (credit M independently unless arrows contradict) (redit possible repeat error from (c)(iii) for M) (If the wrong haloalkane is used OR but-1-ene is produced, award MAX. marks for the mechanism) (If E1 mechanism is used, give full credit in which M1 and M are for correct curly arrows on the correct carbocation) 19. (a) (i) l l l l (ii) step in which radicals are used and formed (iii) l l l l [5] (iv) l l l l 4 (b) Equation l N N N 4 l Mecanism N: l N :N 5 [9] 0. 4 l l l Initiation: l l. Propagation: 4 l.. l. l l l. Termination: l. l. l or [5] Mill ill igh School 11

12 1. Reaction 5 N 1 For Reaction 4; credit dil SO 4 OR SO 4 (aq) OR l (aq) but NOT steam and NOT NaO(aq). nucleophilic substitution 1 (both words needed) [1] Mechanism M1 curly arrow from lone pair on oxygen of hydroxide 1 ion to atom of - Mechanism M curly arrow from - bond to side of atom 1 (a possible repeat error here from Question 4a) (award a maximum of one mark for the wrong haloalkane) (credit an SNl mechanism in which Ml will be a curly arrow from the lone pair on oxygen of the hydroxide ion to the correct positive carbon atom) Y is susceptible to attack by hydroxide ions for one of the following reasons 1 o the - bond is polar o the carbon atom is partially positive (or shown as such) o the carbon atom is electron deficient [4]. (a) Reaction : NaO OR KO M1 alcohol (ic) OR ethanol (ic) M ignore heat ondition mark linked to correct reagent but award M if O or base or alkali mentioned (b) Mechanism: O: M1 M.. ( O L ) l M Award M ( l) independently M1 and M must be to / from correct places E1 mechanism possible in which M Name: of mechanism = elimination NOT dehydrohalogenation Ignore base OR nucleophilic before elimination Reason: Reaction has (very) low yield 5 QoL OR chloroethane has to be made (from ethane) OR chloroethane is expensive OR chloroethane is not redily available [7] Mill ill igh School 1

13 4. (a) Alcohol: Reaction = Substitution (/ hydrolysis) Ignore reference to nucleophilic, but electrophilic give zero Alcohol: Role = nucleophile (/ lone pair donor) Alkene: reaction = elimination Ignore ref to nucleophilic or electrophilic Alkene: base (/ proton acceptor) 4 (b) Alcohol = butan--ol Not -hydroxybutane or but--ol Appropriate structure for (O) ackets not essential S N version S N 1 version δ δ bond is polar bond is polar Lone pair of O bond breaks Attacks the δ forming carbocation / carbonium ion M1 can be scored from a diagram, M and M from written explanation only 5 5. (i) -chloro(--)methylpropane / ()methyl chloropropane 1 (ii) appropriate unambiguous formula for either but-1-ene or but--ene appropriate unambiguous formula for the remaining structural isomer allow 1 mark if candidate draws cis and trans but--ene (iii) unambiguous structure for -methylpropan-1-ol may be from mechanism curly arrow / attack by O curly arrow from lone pair or charge only do not allow if Na -O curly arrow from bond to l / dipole shown on -l bond / intermediate showing full and partial bonds to loss of l Nal or Na :l not allowed 4 [9] if S N 1 mechanism given: first mark as above - independent second mark for correct carbocation formed including curly arrow from to l or S l S third mark for hydroxide attack as above final mark not available (wrong mechanism) penalise missing proton once only [7] Mill ill igh School 1

14 6. O O base O O nucleophile =( ) (O)( ) -methylbut--ene -methylbutan--ol also loss of from or = O - methylbut - l - ene 14 [14] Mill ill igh School 14