Name of mechanism (1) For Step 3, give the reagent, give a necessary condition and name the mechanism. Reagent... Condition...

Transcription

1 Q. A possible synthesis of the amino acid X is shown below. (a) Name and outline a mechanism for Step. Name of mechanism... Mechanism (5) (b) Give the IUPAC name of the product of Step.... () (c) For Step, give the reagent, give a necessary condition and name the mechanism. Reagent... Condition... Name of mechanism... () (d) At room temperature, the amino acid X exists as a solid. Draw the structure of the species present in the solid amino acid. () Page of 54

2 With reference to your answer to part (d), explain why the melting point of the amino acid X is higher than the melting point of CH CH CH(OH)COOH (Extra space)..... () (e) There are many structural isomers of X, CH CH CH(NH )COOH. Draw a structural isomer of X that is an ethyl ester. () Draw a structural isomer of X that is an amide and also a tertiary alcohol. () (iii) Draw a structural isomer of X that has an unbranched carbon chain and can be polymerised to form a polyamide. () Page of 54

3 (f) Draw the structure of the tertiary amine formed when X reacts with bromomethane. () (Total 6 marks) Q. The amide or peptide link is found in synthetic polyamides and also in naturally occurring proteins. (a) Draw the repeating unit of the polyamide formed by the reaction of propanedioic acid with hexane-,6-diamine. () In terms of the intermolecular forces between the polymer chains, explain why polyamides can be made into fibres suitable for use in sewing and weaving, whereas polyalkenes usually produce fibres that are too weak for this purpose. (Extra space)... () Page of 54

4 (b) Name and outline a mechanism for the reaction of CH CH COCl with CH NH Name of mechanism... Mechanism (5) Give the name of the product containing an amide linkage that is formed in the reaction in part (b). () (c) The dipeptide shown below is formed from two different amino acids. Draw the structure of the alternative dipeptide that could be formed by these two amino acids. () Page 4 of 54

5 (d) The amino acids serine and aspartic acid are shown below. Give the IUPAC name of serine. () Draw the structure of the species formed when aspartic acid reacts with aqueous sodium hydroxide. () (iii) Draw the structure of the species formed when serine reacts with dilute hydrochloric acid. () (iv) Draw the structure of the species formed when serine reacts with an excess of bromomethane. () (Total 6 marks) Page 5 of 54

6 Q. (a) Consider the tripeptide shown below that is formed from three amino acids, K, L and M. Name the process by which the tripeptide is split into three amino acids. () Give the IUPAC name for the amino acid K. () (iii) Draw the structure of the zwitterion of amino acid L. () (iv) Draw the structure of the species formed by amino acid M at low ph. () Page 6 of 54

7 (b) Consider the amino acid serine. Draw the structure of the product formed when serine reacts with an excess of CH Br () Draw the structure of the dipeptide formed by two molecules of serine. () (Total 6 marks) Page 7 of 54

8 Q4. (a) Name and outline a mechanism for the reaction of CH CH NH with CH CH COCl Name the amide formed. (6) Page 8 of 54

9 (b) Haloalkanes such as CH Cl are used in organic synthesis. Outline a three-step synthesis of CH CH NH starting from methane. Your first step should involve the formation of CH Cl In your answer, identify the product of the second step and give the reagents and conditions for each step. Equations and mechanisms are not required (6) (Total marks) Page 9 of 54

10 Q5. (a) The repeating units of two polymers, P and Q, are shown below. Draw the structure of the monomer used to form polymer P. Name the type of polymerisation involved. Structure of monomer Type of polymerisation... Draw the structures of two compounds which react together to form polymer Q. Name these two compounds and name the type of polymerisation involved. Structure of compound Name of compound... Structure of compound Name of compound... Type of polymerisation... (iii) Identify a compound which, in aqueous solution, will break down polymer Q but not polymer P. (8) (b) Draw the structures of the two dipeptides which can form when one of the amino acids shown below reacts with the other. Structure Structure () Page 0 of 54

11 (c) Propylamine, CH CH CH NH, can be formed either by nucleophilic substitution or by reduction. Draw the structure of a compound which can undergo nucleophilic substitution to form propylamine. Draw the structure of the nitrile which can be reduced to form propylamine. (iii) State and explain which of the two routes to propylamine, by nucleophilic substitution or by reduction, gives the less pure product. Draw the structure of a compound formed as an impurity. Route giving the less pure product... Explanation... Structure of an impurity (5) (Total 5 marks) Q6. Fibres are made from natural and from synthetic polymers. Both types of polymer have advantages and disadvantages. (a) Amino acids are the building blocks of naturally-occurring polymers called proteins. Consider the following amino acid. Draw the structure of the amino acid species present in a solution at ph. Page of 54

12 Use your understanding of amino acid chemistry to deduce the structure of the dipeptide formed from two molecules of this amino acid and illustrate your answer with a sketch showing the structure of the dipeptide. (iii) Protein chains are often arranged in the shape of a helix. Name the type of interaction that is responsible for holding the protein chain in this shape. () (b) Alkenes are the building blocks of synthetic addition polymers. Consider the hydrocarbon G, (CH ) C=CHCH, which can be polymerised. Draw the repeating unit of the polymer. Draw the structure of an isomer of G which shows E-Z isomerism. (iii) Draw the structure of an isomer of G which does not react with bromine water. () (c) Draw the repeating unit of the polymer formed by the reaction between butanedioic acid and hexane-,6-diamine. () Page of 54

13 (d) Two plastic objects were manufactured, one from the polyalkene represented by the repeating unit in part (b) and the other from the polyamide represented by the repeating unit in part (c). After use it was suggested that both objects be disposed of as landfill. Describe an experiment in which you could compare the biodegradability of these two objects. () Describe an advantage or a disadvantage of a different method of disposal of such objects compared with landfill. () (Total 4 marks) Page of 54

14 Q7. Consider the reaction sequence shown below. (a) Name and outline a mechanism for the reaction in Step. Name of mechanism... Mechanism (5) Page 4 of 54

15 (b) Name compound Q formed in Step. Two stereoisomers are formed by the dehydration of Q. Give the structures of these two isomers and name the type of stereoisomerism shown. Structures of isomers Type of stereoisomerism... (4) (c) An isomer of Q which has the structure shown below is polymerised to form the biodegradeable polymer known as PHB. Draw the repeating unit of the polymer PHB. Suggest a reason why the polymer is biodegradeable. () Page 5 of 54

16 (d) The amino acid R is shown below. Draw the structure of the zwitterion formed by R. Draw the structure of the major organic product formed when an excess of R is reacted with bromomethane. (iii) Name the mechanism of the reaction which results in the formation of the product given in part. () (Total 4 marks) Q8. (a) The structure below shows the repeating unit of a polymer. By considering the functional group formed during polymerisation, name this type of polymer and the type of polymerisation involved in its formation. Type of polymer... Type of polymerisation... () Page 6 of 54

17 (b) Draw the structure of the species present in solid aminoethanoic acid, H NCH COOH () (c) Explain why the melting point of aminoethanoic acid is much higher than that of hydroxyethanoic acid, HOCH COOH () (Total 5 marks) Q9. The amino acid alanine is shown below. (a) A sample of alanine is dissolved in water. Draw the structure of the main alanine species present in this aqueous solution and give the name of this type of species. Structure Type of species... Draw the structure of the alanine species formed when an excess of hydrochloric acid is added to the solution. () Page 7 of 54

18 (b) Alanine molecules may be reacted together to form a polypeptide. Give the repeating unit of this polypeptide and name the type of polymerisation involved in its formation. Repeating unit Type of polymerisation... () (c) The repeating unit of a polyalkene is shown below. Give the name of the alkene which is used to form this polymer.... () (Total 6 marks) Q0. (a) The compound H C=CHCN is used in the formation of acrylic polymers. Draw the repeating unit of the polymer formed from this compound. Name the type of polymerisation involved in the formation of this polymer. () (b) When the dipeptide shown below is heated under acidic conditions, a single amino acid is produced. Name this amino acid. Page 8 of 54

19 Draw the structure of the amino acid species present in the acidic solution. () (c) The repeating unit of a polyester is shown below. Deduce the empirical formula of the repeating unit of this polyester. Draw the structure of the acid which could be used in the preparation of this polyester and give the name of this acid. Structure... Name... (iii) Give one reason why the polyester is biodegradable. (4) (Total 8 marks) Page 9 of 54

20 Q. Three sections of the proton n.m.r. spectrum of CH CHClCOOH are shown below. (a) Name the compound CH CHClCOOH... () (b) Explain the splitting patterns in the peaks at δ.7 and δ () (c) Predict the splitting pattern that would be seen in the proton n.m.r. spectrum of the isomeric compound ClCH CH COOH () Page 0 of 54

21 (d) The amino acid alanine is formed by the reaction of CH CHClCOOH with an excess of ammonia. The mechanism is nucleophilic substitution. Outline this mechanism, showing clearly the structure of alanine. (5) (e) The amino acid lysine has the structure Draw structures to show the product formed in each case when lysine reacts with an excess of aqueous HCl, an excess of aqueous NaOH, (iii) another molecule of lysine. () (Total marks) Page of 54

22 Q. (a) Synthetic polyamides are produced by the reaction of dicarboxylic acids with compounds such as H N(CH ) 6 NH Name the compound H N(CH ) 6 NH Give the repeating unit in the polyamide nylon 6,6. () (b) Synthetic polyamides have structures similar to those found in proteins. Draw the structure of -aminopropanoic acid. Draw the organic product formed by the condensation of two molecules of - aminopropanoic acid. () (c) Compounds like H N(CH ) 6 NH are also used to make ionic compounds such as X, shown below. X belongs to the same type of compound as (CH ) 4 N + Br Name this type of compound. State a reagent which could produce X from H N(CH ) 6 NH and give a necessary condition to ensure that X is the major product. Reagent... Condition... Page of 54

23 (iii) Name the mechanism involved in this reaction to form X. (4) (Total 8 marks) Q. (a) Consider the following amino acid. Draw the structure of the amino acid species present in a solution at ph. Draw the structure of the dipeptide formed from two molecules of this amino acid. (iii) Protein chains are often arranged in the shape of a helix. Name the type of interaction that is responsible for holding the protein chain in this shape. () Page of 54

24 (b) Consider the hydrocarbon G, (CH ) C=CHCH, which can be polymerised. Name the type of polymerisation involved and draw the repeating unit of the polymer. Type of polymerisation... Repeating unit Draw the structure of an isomer of G which shows geometrical isomerism. (iii) Draw the structure of an isomer of G which does not react with bromine water. (4) (Total 7 marks) Q4. The structures of the amino acids alanine and glycine are shown below. (a) Give the systematic name for alanine.... () Page 4 of 54

25 (b) Alanine exists as a pair of stereoisomers. Explain the meaning of the term stereoisomers. State how you could distinguish between the stereoisomers. (4) (c) Give the structural formula of the species formed by glycine at ph 4. () (d) When two amino acids react together, a dipeptide is formed. Give the structural formulae of the two dipeptides which are formed when alanine and glycine react together. Dipeptide Page 5 of 54

26 Dipeptide () (e) Give the structural formula of the organic compound formed when glycine reacts with methanol in the presence of a small amount of concentrated sulphuric acid. () (Total 9 marks) Page 6 of 54

27 Q5. The amino acids aspartic acid and phenylalanine react together to form a dipeptide. This dipeptide can be converted into a methyl ester called aspartame. Aspartame has a sweet taste and is used in soft drinks and in sugar-free foods for people with diabetes. Hydrolysis of aspartame forms methanol initially. After a longer time the peptide link breaks to form the free amino acids. Neither of these amino acids tastes sweet. (a) Apart from the release of methanol, suggest why aspartame is not used to sweeten foods that are to be cooked (Extra space) () (b) Give the IUPAC name of aspartic acid.... () (c) Draw the organic species formed by aspartic acid at high ph. () (d) Draw the zwitterion of phenylalanine. () Page 7 of 54

28 (e) Phenylalanine exists as a pair of stereoisomers. State the meaning of the term stereoisomers () Explain how a pair of stereoisomers can be distinguished (Extra space)..... () (Total 8 marks) Q6. (a) Name compound Y, HOCH CH COOH... () (b) Under suitable conditions, molecules of Y can react with each other to form a polymer. Draw a section of the polymer showing two repeating units. () Name the type of polymerisation involved. () Page 8 of 54

29 (c) When Y is heated, an elimination reaction occurs in which one molecule of Y loses one molecule of water. The organic product formed by this reaction has an absorption at 67 cm in its infrared spectrum. Identify the bond that causes the absorption at 67 cm in its infrared spectrum. () Write the displayed formula for the organic product of this elimination reaction. () (iii) The organic product from part can also be polymerised. Draw the repeating unit of the polymer formed from this organic product. () (d) At room temperature, -aminobutanoic acid exists as a solid. Draw the structure of the species present in the solid form. () (e) The amino acid, glutamic acid, is shown below. Draw the structure of the organic species formed when glutamic acid reacts with each of the following. an excess of sodium hydroxide () Page 9 of 54

30 an excess of methanol in the presence of concentrated sulfuric acid () (iii) ethanoyl chloride () (f) A tripeptide was heated with hydrochloric acid and a mixture of amino acids was formed. This mixture was separated by column chromatography. Outline briefly why chromatography is able to separate a mixture of compounds. Practical details are not required () (Total marks) Q7. The three amino acids shown below were obtained by hydrolysis of a protein. (a) Draw the zwitterion of alanine. () Page 0 of 54

31 Draw the species formed when valine is dissolved in an alkaline solution. () (iii) Draw the species formed by lysine at low ph. () (b) Draw the two dipeptides formed by the reaction of alanine with valine. () (c) Name a suitable method by which the mixture of amino acids formed by hydrolysis of the protein can be separated.... () (Total 6 marks) Page of 54

32 Don t penalize position of + on NH M. (a) allow :CN M not allowed independent of M, but allow M for correct attack on C+ + rather than δ+ on C=O loses M M is for correct structure including minus sign but lone pair is part of M4 Allow C H 5 M and M4 for lp and curly arrow 4 (b) -bromobutanenitrile Allow -bromobutane--nitrile (c) M ammonia or NH Ignore temp or pressure M excess (ammonia) excess tied to NH and may score in M unless contradicted Ignore concentrated or sealed container, Acid loses conditions mark M nucleophilic substitution Allow close spelling (d) Allow C H 5 Allow CO Allow + NH Page of 54

33 Allow NH M electrostatic forces between ions in X QOL Allow ionic bonding. Marks independent M (stronger than) hydrogen bonding between CH CH CH(OH)COOH CE mention of molecules of X or inter molecular forces between X loses both marks (e) OR Isomer of C 4 H 9 NO Isomer of C 4 H 9 NO allow NH Allow (iii) H N CH CH CH COOH or H N (CH ) COOH Isomer of C 4 H 9 NO allow NH OR Do not allow C H 6 - Beware do not credit X itself Page of 54

34 (f) Answer has 6 carbons so NOT isomer of X Allow C H 5 Must have bond from C to N not to methyl group [6] M. (a) Allow CONH- or - COHN - Mark two halves separately lose each for missing trailing bonds at one or both ends or error in peptide link or either or both of H or OH on ends Not allow (C 6 H ) Ignore n M in polyamides - H bonding M in polyalkenes - van der Waals forces Penalise forces between atoms or van der Waals bonds M Stronger forces (of attraction) in polyamides Or H bonding is stronger (must be a comparison of correct forces to score M) Do not award if refer to stronger bonds Page 4 of 54

35 (b) (nucleophilic) addition elimination Minus sign on NH loses M M not allowed independent of M, but allow M for correct attack on C+ + rather than + on C=O loses M If Cl lost with C=O breaking, max for M M for correct structure with charges but lp on O is part of M4 only allow M4 after correct/ very close M For M4, ignore NH removing H + but lose M4 for Cl removing H + in mechanism, but ignore HCl as a product N-methylpropanamide Not N-methylpropaneamide 4 (c) Allow CONH or COHN Page 5 of 54

36 allow NH don t penalize position of + on NH (d) -amino--hydroxypropanoic acid Must be salts of aspartic acid allow CO (iii) Penalise use of aspartic acid once in d(iii) and d(iv) allow CO H allow + NH (iv) Penalise use of aspartic acid once in d(iii) and d(iv) (Br ) allow CO must show C-N bond don t penalize position of + on N(CH ) [6] Page 6 of 54

37 don t penalize position of + on NH M. (a) hydrolysis not hydration -aminopropanoic acid ignore alanine QoL (iii) allow CO allow + NH (iv) allow CO allow + NH don t penalize position of + on NH (b) allow CO H allow limit as + on N or outside [ ] Page 7 of 54

38 allow CO H allow CONH or COHN allow NH allow limit as [6] M4. (a) (nucleophilic) addition-elimination 4 N-ethylpropanamide minus on NH loses M M not allowed independent of M, but allow M for correct attack on C+ +C=O loses M only allow M4 after correct or very close M lose M4 for Cl removing H + in mechanism, but ignore HCl as a product Not N-ethylpropaneamide Page 8 of 54

39 M5. (a) CH CH=CHCH (b) CH CN or ethan(e)nitrile or ethanonitrile not ethanitrile but allow correct formula with ethanitrile for each step wrong or no reagent loses condition mark contradiction loses mark Step Cl uv or above 00 C wrong or no reagent loses condition mark Step KCN aq and alcoholic (both needed) allow uv light/(sun)light/uv radiation Step H /Ni or LiAlH 4 or Na/C H 5 OH not CN but mark on NOT HCN or KCN + acid, and this loses condition mark NOT NaBH 4 Sn/HCl (forms aldehyde!) ignore conditions [] Addition or radical (QoL) CH CH(OH)CH(OH)CH or with no brackets butan(e), diol or, butan(e)diol, dimethylbutan(e)dioic acid ignore,4 condensation (QoL), dimethylbutan(e)dioyl chloride Page 9 of 54

40 (iii) NaOH or HCl etc or Na CO Allow conc sulphuric/nitric NOT water nor acidified water nor weak acids (b) Structure Allow CONH and COHN Allow zwitterions NOT polypeptides/repeating units Structure either of (c) CH CH CH Br CH CH CN allow Cl, I (iii) (nucleophilic) substitution or from CH CH CH Br if reduction written here, no further marks further substitution/reaction occurs or other products are formed Allow reduction forms only one product one of (CH CH CH ) NH (CH CH CH ) N (CH CH CH ) 4 N + Br Allow salts including NH 4 Br Allow HBr [5] Page 40 of 54

41 M6. (a) (iii) hydrogen bonding (do not allow H-bonding) QWC do not penalise any error twice. (b) (iii) Isomer must be saturated or must not contain a double bond (c) (d) heat/reflux with aqu NaOH poly(alkene) is inert/ no reaction polyamide is hydrolysed (or undergoes hydrolysis) to form acid salt and alcohol QWC Page 4 of 54

42 e.g combustion heat energy produced toxic gases produced [4] M7. (a) necleophilic addition; M structure; (be lenient on position of charge on CN ) (M not allowed independent of M, but allow M for correct attack on C+ if M show as independent first.) (+on C of C=O loses M but ignore δ+ if correct) (M4 for arrow and lone pair (only allow for correct M or close)) 4 (b) -hydroxybutanoic acid geometric(al) or cis-trans (c) (one unit only) (ignore brackets or n) (trailing bonds are needed) Page 4 of 54

43 can be hydrolysed OR can be reacted with/attacked by acid/base/nucleophiles/h O/OH ; (d) (allow NH + ) (or zwitterions product) (iii) nucleophilic substitution; [4] M8. (a) polyamide or nylon (,4) condensation (allow nylon without numbers but if numbers are present they must be correct) (b) (c) ionic bonding in aminoethanoic acid (can only score if includes that aminoethanoic is ionic) stronger attractions than Hydrogen bonding in hydroxyethanoic acid (e.g. stronger Hydrogen bonding in aminoethanoic acid scores 0) (mention of electrostatic forces between molecules scores 0) [5] Page 4 of 54

44 M9. (a) penalise + NH or + on H once per paper zwitterions (b) ignore n, but allow one drawn out repeating unit only condensation or (nucleophilic) addition-elimination (c) -methylpent--ene [6] M0. (a) (Ignore n or brackets, but trailing bonds are essential) Addition or radical (b) -aminobutanoic (acid) Page 44 of 54

45 (c) C H 4 O Allow S N 5 (,4-)butan(e)dioic (acid) (allow succinic, but not dibutanoic nor butanedicarboxylic acid) (iii) Can be hydrolysed / can react with acid or base or water / can react with nucleophiles [8] M. (a) -chloropropanoic acid () (b) δ.7 Doublet next to CH () δ 4.44 Quartet next to CH () (c) Two triplets () (d) (e) Page 45 of 54

46 (iii) Or anhydride [] M. (a) hexane-,6-diamine or,6-diaminohexane (allow ammine) or,6 hexan(e)diamine () Allow CONH (b) Page 46 of 54

47 (c) quaternary ammonium bromide salt () (not ion, not compound) Allow quarternery Reagent: CH Br or bromomethane () penalise CH Cl but allow excess for any halomethane Condition: excess (CH Br) () (iii) nucleophilic substitution () 4 [8] (a) () M. ignore Na + unless covalently bonded () must be dipeptide, not polymer nor anhydride allow CONH or COHN allow zwitterion (iii) hydrogen bonding () QL Allow with dipole-dipole or v derwaals, but not dipole-dipole etc alone (b) Type of polymerisation: addition(al) () Repeating unit: () not multiples allow n Page 47 of 54

48 CH CH=CHCH CH () C H 5 (iii) 4 [7] M4. (a) -amino(e) propanoic acid () (b) molecules with same structure / structural formula () but with bonds (atoms or groups) arranged differently in space (D) () Plane polarised light () Rotated (equally) in opposite directions () (c) () 4 allow H NCH COO Penalise NH - and OH- once per paper but CH is allowed (d) Not anhydrides; not repeating units Page 48 of 54

49 or H NCH COOCH allow NH don t penalize position of + on NH (e) () [9] M5. (a) Heating speeds up (hydrolysis / breaking of peptide bonds) OR forms non-sweet (amino acids) (b) (-)aminobutanedioic acid OR not necessary but penalise other numbers at start (-)aminobutane(-,4-)dioic acid,4 not necessary but penalise other numbers and,4 must be in correct place (QoL) (c) allow CO (d) allow CO allow +NH (e) M Compounds/molecules with same structural formula Not just structure M But with bonds/atoms/groups arranged differently in space or in D Allow with different spatial arrangement of atom/bond/group Independent marks Page 49 of 54

50 (Plane) polarised light Rotated in opposite directions Not bent or turned or twisted; not different directions (QoL) [8] M6. (a) -hydroxypropanoic acid allow -hydroxypropionic acid must be correct spelling (b) must show trailing bonds or can start at any point in the sequence, e.g. not allow dimer allow O CH CH COOCH CH CO or CH CH COOCH CH COO ignore ( ) or n NB answer has a total of 6 carbons and 4 oxygens condensation (polymerisation) Allow close spelling (c) C=C or carbon-carbon double bond must show ALL bonds including O H Page 50 of 54

51 (iii) must show trailing bonds allow polyalkene conseq on their c ignore n (d) allow NH + allow COO (e) In (e), do not penalise a slip in the number of carbons in the - CH CH - chain, but all must be bonded correctly NB two carboxylate groups Allow COONa or COO Na + but not covalent bond to Na allow NH In (e), do not penalise a slip in the number of carbons in the -CH CH - chain, but all must be bonded correctly NB two ester groups allow NH or + NH Page 5 of 54

52 don t penalize position of + on NH (iii) In 4(e), do not penalise a slip in the number of carbons in the - CH CH - chain, but all must be bonded correctly allow anhydride formation on either or both COOH groups (see below) with or without amide group formation (f) M phase or eluent or solvent (or named solvent) is moving or mobile M M stationary phase or solid or alumina/silica/resin separation depends on balance between solubility or affinity (of compounds) in each phase OR different adsorption or retention OR (amino acids have) different R f values OR (amino acids) travel at different speeds or take different times [] M7. (a) allow CO allow + NH Page 5 of 54

53 allow C H 7 don t penalize position of + on NH allow CO allow NH (iii) allow CO H allow + NH (b) allow CO H allow NH allow C H 7 allow as zwitterions if error in peptide link e.g. if twice, penalise both times not polymers if wrong amino acid in both can score Max (c) chromatography or electrophoresis ignore qualification to chromatography [6] Page 5 of 54

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