QUESTIONSHEETS TEST QUESTION ON ISOMERISM STRUCTURES OF CYCLOALKENES BOND TYPE AND REACTIVITY REACTION CONDITIONS AND PRODUCT

Transcription

1 CHEMISTRY QUESTIONSHEETS A2 Level A2 TOPIC 23 ORGANIC CHEMISTRY (INTRODUCTION AND REACTIONS) Questionsheet 1 Questionsheet 2 Questionsheet 3 Questionsheet 4 Questionsheet 5 Questionsheet 6 Questionsheet 7 Questionsheet 8 Questionsheet 9 Questionsheet 10 Questionsheet 11 Questionsheet 12 Questionsheet 13 Questionsheet 14 Questionsheet 15 Questionsheet 16 Questionsheet 17 Questionsheet 18 Questionsheet 19 Questionsheet 20 Questionsheet 21 Questionsheet 22 Questionsheet 23 Questionsheet 24 Questionsheet 25 Questionsheet 26 Questionsheet 27 E/Z (CIS/TRANS) ISOMERISM OPTICAL ISOMERISM TEST QUESTION ON ISOMERISM STRUCTURE OF BENZENE STRUCTURES OF CYCLOALKENES BOND TYPE AND REACTIVITY REACTION CONDITIONS AND PRODUCT NITRATION OF ARENES HALOGENATION OF ARENES ALKYLATION AND ACYLATION OF ARENES PHENOL ALDEHYDES AND KETONES USE OF 2,4-DINITROPHENYLHYDRAZINE THE TRIIODOMETHANE REACTION GRIGNARD REAGENTS CARBOXYLIC ACIDS I CARBOXYLIC ACIDS II ACYL CHLORIDES ESTERS NITRILES AMIDES AMINES DIAZOTISATION AMINO ACIDS PROTEINS TEST QUESTION I TEST QUESTION II 17 marks 23 marks 16 marks 13 marks 17 marks 17 marks 16 marks 14 marks 11 marks 13 marks 18 marks 10 marks 20 marks 14 marks 16 marks 15 marks 20 marks 16 marks 17 marks 15 marks 14 marks 20 marks 17 marks 13 marks 13 marks 12 marks 11 marks Curriculum Press Bank House 105 King Street Wellington Shropshire TF1 1NU

2 TOPIC 23 Questionsheet 1 E/Z (CIS/TRANS ISOMERISM) a) Explain why there are two stereoisomers of pent-2-ene. Sketch their structures and name them. Explanation... Structures and names [4] b) Suggest why 1,2-dichlorocyclopentane can exhibit the same type of isomerism. Sketch the two structures. Suggestion... [1] Structures c) Inspect each of the following compounds and state whether or not it can exhibit geometrical isomerism. In the light of your answers, state what structural feature (apart from C=C) is necessary for the existence of E/Z isomers. =CH... [1] ( ) 2 C=... [1] CHCl=CHCl... [1] CHCl=CH... [1] CHCl=CCl... [1] CH=CCl... [1] Structural feature... [2] TOTAL / 17

3 TOPIC 23 Questionsheet 2 OPTICAL ISOMERISM a) Draw the structures of the two stereoisomers of butan-2-ol and state how they can be distinguished in the laboratory. Structures Means of distinguishing between them... [2] [3] Why is it that, although butan-2-ol can exhibit this type of isomerism, its oxidation product, butanone, does not? b) A chemist, who synthesised 2-hydroxypropanoic acid (lactic acid) by reacting ethanal with hydrogen cyanide and then boiling the product with concentrated hydrochloric acid, reported that the 2- hydroxypropanoic acid was an equal mixture of enantiomers. What are enantiomers? How did the chemist know that an equal mixture had been formed? (iii) What name is given to such a mixture? (iv) Explain why such a mixture is formed.... [4] TOTAL (Continued...) /

4 TOPIC 23 Questionsheet 2 Continued OPTICAL ISOMERISM c) On the structures shown below, mark any chiral centre using *. There may be none or one or more centres per molecule. H CH C NH 2 O O H H H H H C C C C H H O H H C H H H NH 2 C C H HO HO H C OH H C N H H OH H C C Cl N O C O CH CHCl C O [6] d) L-dopa, the drug used to treat Parkinson s disease, is a single optical isomer. Explain why pharmaceutical companies choose to use medicines containing only the single isomer. TOTAL / 23

5 TOPIC 23 Questionsheet 3 TEST QUESTION ON ISOMERISM a) In the context of isomerism, compounds of molecular formula C 4 H 10 O are particularly interesting, because they can exhibit skeletal isomerism, positional isomerism, functional group isomerism and stereoisomerism. Illustrate this statement by writing the structural formulae of suitable pairs of compounds to show each kind of isomerism. Skeletal isomerism... [2] Positional isomerism... [2] Functional group isomerism... [2] Stereoisomerism [2] Explain why it is that compounds of molecular formula C 4 H 10 O can exhibit one kind of stereoisomerism but not another.... [4] b) Butanone and phenylhydrazine react together as shown by the following equation to give butanone phenylhydrazone, a compound which exhibits stereoisomerism. C 2 H 5 C 2 H 5 C = O + H 2 N NHC 6 H 5 C = N NHC 6 H 5 + H 2 O What kind of stereoisomerism is shown by butanone phenylhydrazone? Draw the structural formulae of the two stereoisomers. [2] (iii) State one physical property which could help you to distinguish between the stereoisomers. TOTAL / 16

6 TOPIC 23 Questionsheet 4 STRUCTURE OF BENZENE a) Cyclohexene, C 6 H 10, reacts with hydrogen to form cyclohexane, C 6 H 12. The enthalpy of hydrogenation is 120 kj mol -1. Suggest the conditions that would be used for this reaction. Give the structure of the hypothetical species cyclohexa-1,3,5-triene. [1] (iii) Calculate the value you would expect for the enthalpy of hydrogenation of this species. (iv) Benzene, C 6 H 6, has essentially the same formula as cyclohexa-1,3,5-triene, but its enthalpy of hydrogenation is only 208 kj mol -1. Comment upon the difference between this value and that obtained in a) (iii)....[3] b) The structure of benzene is said to consist of a 6-membered carbon ring, with a system of delocalised electrons. Although unsaturated, it exhibits different reactions from those of the alkenes. Explain the meaning of the terms delocalised and unsaturated. Delocalised [2] Unsaturated... [1] What structure would you expect benzene to have if it showed reactions similar to the alkenes? [1] (iii) Give three pieces of evidence that benzene does not have such a structure. TOTAL / 13

7 TOPIC 23 Questionsheet 5 STRUCTURES OF CYCLOALKENES I II III a) Name the alkenes I, II and III. Alkene I... [1] Alkene II... [1] Alkene III... [1] b) Complete the following equations for the complete hydrogenation of alkenes I and II H 2 Hê = kj r mol-1 [1] H 2 Hê = kj r mol-1 [1]... c) Use the molar enthalpies of hydrogenation shown in b) to draw what conclusions you can about the bonding between the carbon atoms in alkene II.... [4] d) How would you expect the lengths of the carbon-carbon bonds in alkene II to compare with one another? In your answer, refer to the bonds by the letters a, b, c, d, e and f as shown below. f a e d b c... [4] e) Estimate, with reasons, the molar enthalpy of hydrogenation of alkene III. Estimate... [1] Reasons... TOTAL / 17

8 TOPIC 23 Questionsheet 6 BOND TYPE AND REACTIVITY a) Alkenes are readily attacked by electrophiles, but alkanes resist attack by both electrophiles and nucleophiles. Give two reasons for the high reactivity of alkenes towards electrophiles [2] Give two reasons for the low reactivity of alkanes [2] b) The negative inductive effect (-I effect) is said to be responsible for the nucleophilic substitution reactions of haloalkanes. What is the immediate consequence of the negative inductive effect, and what is responsible for it? List the haloalkanes RBr, RCl and RI in increasing order of reactivity in nucleophilic substitution reactions. (iii) Explain your answer to b). c) Despite the strength of the C=O bond (average bond enthalpy = 743 kj mol -1 ), aldehydes and ketones react readily with numerous reagents, e.g. HCN. What type of reagent attacks aldehydes and ketones? Give two reasons why species such as CN - are strongly attracted to the carbonyl carbon atom of an aldehyde or ketone [2] (iii)when HCN reacts with an aldehyde or ketone, why does an addition reaction occur rather than substitution? (iv) Species, such as CN -, which react with aldehydes and ketones, do not generally attack alkenes. Why is this? (v) It can be argued that HCN should react with alkenes in the same way as HBr, yet this does not happen. Explain this. TOTAL / 17

9 TOPIC 23 Questionsheet 7 REACTION CONDITIONS AND PRODUCT a) In the presence of ultraviolet light, methylbenzene reacts with chlorine to give (chloromethyl)benzene: Cl + Cl2 + HCl The mechanism resembles that for the chlorination of methane. Name this mechanism. What type of fission does the chlorine molecule undergo? (iii) Write likely equations for the three mechanistic stages. Stage 1 Stage 2 [1] Stage 3 [2] b) In the absence of ultraviolet light, methylbenzene reacts with chlorine to give an entirely different product. Write an equation for this reaction. [1] [1] Name a suitable catalyst for the reaction. (iii) What type of mechanism is involved? (iv) What type of fission does the chlorine molecule undergo? c) By referring to the chemistry of a haloalkane of your own choice, give another example of the way in which the product of a reaction can be completely altered by changing the conditions. In your answer you should mention reaction conditions, identity of products, and types of mechanism.... [6] TOTAL / 16

10 TOPIC 23 Questionsheet 8 NITRATION OF ARENES a) Give the reagents, conditions and equation for the mononitration of benzene. Reagents... [2] Conditions... [1] Equation b) In what way must the conditions be modified when carrying out the mononitration of methylbenzene (toluene)? [1] Suggest two ways in which the conditions could be changed so as to bring about dinitration or polynitration of arenes [2] (iii) Write down the formula of the end-product of the trinitration of methylbenzene and state the use of this compound. Formula Use... [1] c) Nitroarenes can be converted to primary aromatic amines. [1] Write an equation for the conversion of nitrobenzene to phenylamine. What type of reaction is this? (iii) What reagent (or reagents) would be used for this conversion in the laboratory? (iv) Of what commercial importance is this type of reaction? TOTAL / 14

11 TOPIC 23 Questionsheet 9 HALOGENATION OF ARENES a) Cyclohexene and benzene are both cyclic hydrocarbons with a six-membered carbon ring, yet they behave very differently in their reactions with halogens. State the conditions and write an equation for the reaction between bromine and cyclohexene. Conditions... [2] Equation [1] What type of reaction is this? b) State the conditions and write an equation for the reaction between bromine and benzene. Conditions... [2] Equation [1] What type of reaction is this? c) How do you account for the relative resistance to bromination of benzene compared with cyclohexene? TOTAL / 11

12 TOPIC 23 Questionsheet 10 ALKYLATION AND ACYLATION OF ARENES a) Benzene can be converted into methylbenzene by a so-called Friedel-Crafts reaction. Name a suitable reagent for the conversion, state the reaction conditions, and write an equation. Reagent... [1] Conditions... [2] Equation [1] What is the major disadvantage of this method of preparing methylbenzene? (iii) How could methylbenzene be converted into benzenecarboxylic acid? State the type of reaction and suggest a suitable reagent. Type of reagent... [1] Reagent... [1] b) How does benzene react with ethanoyl chloride? State the reaction conditions, write an equation and name the product. Conditions... [2] Equation Name of product... [1] [1] How could the product of b) be converted into 1-phenylethanol? State the type of reaction and suggest a suitable reagent. Type of reaction... [1] Reagent... [1] TOTAL / 13

13 TOPIC 23 Questionsheet 11 PHENOL a) OH OH OH OH OH I II III IV Compounds I-IV are all aromatic hydroxy-compounds, yet not all of them are phenols. Identify the phenols and give the basis of your identification. Identity of phenols... [1] Basis of identification... b) To demonstrate its acidic character, phenol (which has a low solubility in water) can be dissolved in aqueous sodium hydroxide to give a colourless solution, A. On adding dilute hydrochloric acid, this solution becomes cloudy at first and then separates to give a colourless oil, B, as a lower layer. Identify A and B, and write equations for the reactions involved. Identity of A... [1] Identity of B... [1] Equations [2] Give two reasons which together explain the fact that phenols are acidic, although alcohols have almost no acidic properties. Reason [3] Reason [3] c) State what is observed when bromine water is added to an aqueous solution of phenol. Write an equation for the reaction. [1] (iii) How do you account for the relative ease of bromination of phenol compared with benzene? d) State one use of phenols in everyday life. TOTAL / 18

14 TOPIC 23 Questionsheet 12 ALDEHYDES AND KETONES a) A CHO B ( ) 2 CHCHO C CO From the above list, select all the compounds which satisfy the following requirements. Write down their letters and name them. Could be reduced to a secondary alcohol. Could be oxidised to a carboxylic acid. b) Aldehydes can be distinguished from ketones by their reaction with Tollens reagent (ammoniacal silver nitrate or diammine silver(1)) Describe what you would see with an aldehyde What would propanal become when treated with Tollens reagent (iii) Name a reagent that could be used in place of Tollens reagent for this test and state the observation with the aldehyde. Reagent... Observation [2] c) Aldehydes and ketones can be reduced to alcohols by a reducing agent. Name a reducing agent.. State the conditions under which this reagent is used. TOTAL / 10

15 TOPIC 23 Questionsheet 13 USE OF 2,4-DINITROPHENYLHYDRAZINE A compound contains C 69.8% H 11.6% O 18.6% Its mass spectrum shows that its relative molecular mass is 86. On treatment with 2,4-dinitrophenylhydrazine, an orange-yellow crystalline precipitate is produced. a) Determine the molecular formula of the compound.... [4] b) Give the structural formulae of all the relevant isomers and classify each one as an aldehyde or a ketone.... [7] c) Write an equation to show how any one of these compounds will react with 2,4-dinitrophenylhydrazine. [2] d) Give one chemical method of distinguishing the aldehydes from the ketones. State the reagent you would use, the conditions of the test, and what would expect to observe with aldehydes and with ketones. Test... [1] Conditions... [1] Observation with aldehydes... [1] Observation with ketones... [1] e) The precipitate obtained when an aldehyde or ketone is reacted with 2,4-dinitrophenylhydrazine can be used to identify the original compound if its melting point is determined. How can this melting point be used to identify the original carbonyl compound? What must be done to the precipitate before the melting point is determined and why? TOTAL / 20

16 TOPIC 23 Questionsheet 14 THE TRIIODOMETHANE REACTION a) Ethanal reacts with a solution of iodine in KI(aq), followed by a limited amount of NaOH(aq), to give triiodomethane. What is observed? Write balanced chemical equations for the two reactions which occur. (iii) If excess NaOH(aq) is used, no precipitate is formed. Suggest what causes this difference (iv) Explain why a mixture of KI(aq) and NaClO(aq) could be used instead of iodine solution.... [2] b) The group CO is essential for the production of triiodomethane. Bearing this in mind, suggest why compounds with the CH(OH) group undergo this reaction compounds with the COO - group do not undergo this reaction c) Study the following compounds, and write down the reference letters of all those which will produce triiodomethane on treatment with iodine and sodium hydroxide. A C 6 H 5 CO F CH(OH) B C 6 H 5 COO G CH(OH)C 2 H 5 C C 6 H 5 COC 2 H 5 H ( ) 3 COH D CHO I C 2 H 5 CH(OH)C 2 H 5 E COC 2 H 5 J OH... [4] TOTAL / 14

17 TOPIC 23 Questionsheet 15 GRIGNARD REAGENTS a) Describe the preparation of methylmagnesium iodide and write an equation for its formation. Preparation... Equation... [4] b) Starting from methylmagnesium iodide, how would you prepare ethanol, and ethanoic acid? In each case name the required reagent, show the structure of the intermediate, and state any necessary conditions for the second stage. Ethanol Reagent... [1] Intermediate [1] Conditions for second stage... [1] Ethanoic acid Reagent... [1] Intermediate [1] Conditions for second stage... [1] c) Methylmagnesium iodide was allowed to react with each of two isomeric compounds A and B of molecular formula C 3 H 6 O. The final products were isomeric compounds C and D, of molecular formula C 4 H 10 O. The mass spectrum of C showed peaks at m/z values of 29 and 30, but that of D did not. Identify A, B, C and D, and suggest the species responsible for the peaks mentioned in the mass spectrum of C.... [6] TOTAL / 16

18 TOPIC 23 Questionsheet 16 CARBOXYLIC ACIDS I a) Ethanoic acid reacts with aqueous potassium hydroxide, and solid magnesium oxide? Name the product and type of reaction in each case, and give a balanced equation. aqueous potassium hydroxide Product... [1] Type of reaction... [1] Equation... [1] solid magnesium oxide Product... [1] Type of reaction... [1] Equation... [1] b) Give a reagent that can be used, at room temperature, to show that an unknown organic compound is a carboxylic acid rather than an alcohol. State your expected observation, and write an equation to show this reagent reacting with a carboxylic acid, RCOOH. Reagent... [1] Observation... [1] Equation... [1] c) Butyl ethanoate ( pear drops ) is a useful solvent for cellulose lacquers, but occurs naturally only in traces. How can it be made synthetically? Name the reagents you would use, state the reaction conditions, write an equation and describe the type of reaction occurring. Reagents... [3] Conditions... [1] Equation... [1] Type of reaction... TOTAL / 15

19 TOPIC 23 Questionsheet 17 CARBOXYLIC ACIDS II a) How do you explain the following facts? Carboxylic acids have lower pk a values than alcohols, showing that they are more strongly acidic. Trichloroethanoic acid is a relatively strong carboxylic acid.... [4] b) Starting with propanoic acid, how could you obtain propanoyl chloride and then propanamide? Give a reagent and write an equation for each reaction. Reagent... [1] Equation... [1] Reagent... [1] Equation... [1] c) Benzene-1,4-dicarboxylic acid has the normal reactions of a carboxylic acid. Describe how would you expect it to react with each of the following reagents and give the formula of the organic product. Aqueous sodium carbonate Description [2] Formula of product... [1] Methanol Description [2] Formula of product... [1] d) Benzene-1,2-dicarboxylic acid is an isomer of benzene-1,4-dicarboxylic acid. Which of the two isomers would you expect to have the higher melting point? Give your reasons. TOTAL / 20

20 TOPIC 23 Questionsheet 18 ACYL CHLORIDES a) The ester, ethyl propanoate, can be prepared by the reaction between ethanol and propanoic acid. This method, however, is not entirely satisfactory. Name an acyl chloride which could be used instead of propanoic acid, and state two advantages and two disadvantages of doing so. Name... [1] Two advantages... Two disadvantages... b) Acyl chlorides can also be used to prepare other derivatives of carboxylic acids, such as amides. What acyl chloride and what reagent would be needed to prepare benzenecarboxamide (benzamide)? Acyl chloride... [1] Reagent... [1] What type of reaction is this? (iii) What problem might be encountered when carrying out such preparations in the laboratory? Explain the chemical origin of the problem, and state what precaution could be taken to minimise it. Problem... [1] Origin... [1] Precaution... [1] c) Certain acyl chlorides are useful reagents for the positive identification of amines. Describe how ethanoyl chloride can be used to confirm the identity of an amine, believed (from its boiling point) to be ethylamine. Write an equation for the reaction occurring in c) and name the product. Equation... [1] Name... [1] TOTAL / 16

21 TOPIC 23 Questionsheet 19 ESTERS a) Give the structural formulae and names of three isomeric esters of molecular formula C 4 H 8 O [6] b) Study the following scheme and answer the questions below. Conversion 1 O O C O C O Boil under reflux with NaOH(aq) Then acidify with dil. HCl(aq) Compound 1 Compound II Compound III Complete Conversion 1 by writing down the structural formulae of Compound II (molecular formula C 2 H 6 O 2 ) and Compound III (C 4 H 8 O 2 ) [2] What types of compound are I, II and III? Compound I... [1] Compound II... [1] Compound III... [1] (iii) What type of reaction is represented by Conversion 1? (iv) Why is Conversion 1 carried out using aqueous sodium hydroxide rather than aqueous mineral acid? c) Give three commercial applications of esters. TOTAL / 17

22 TOPIC 23 Questionsheet 20 NITRILES 4.0 g of an aliphatic nitrile, G, was boiled under reflux with excess sodium hydroxide solution until reaction was complete. The reaction mixture was then acidified with excess dilute sulfuric acid to displace the organic acid, H. After distillation, a total of 4.5 g of H were recovered. 1.0 g of H was then diluted to 250 cm 3 with water; 25.0 cm 3 of this solution required cm 3 of 0.1 M sodium hydroxide solution for complete neutralisation. a) Calculate the relative molecular mass of H. b) Identify H, and hence identify G.... [4] c) Write the equation for: the reaction of G with aqueous sodium hydroxide. the subsequent reaction with dilute sulfuric acid. d) Calculate the percentage yield of H. e) How could the nitrile G be reduced? Suggest a suitable reducing agent, together with any conditions, and write an equation. Reducing agent... [1] Conditions... [1] Equation... [1] TOTAL / 15

23 TOPIC 23 Questionsheet 21 AMIDES a) It is possible to convert an amide into two primary amines. Scheme A shows how ethanamide can be converted to ethylamine. How can it be converted to methylamine? Scheme A CONH 2 Ethanamide Li[AlH 4 ] in dry ether NH 2 Ethylamine NH 2 Methylamine b) Nitriles have been described as the anhydrides of amides. Give the name and formula of the nitrile which can be regarded as the anhydride of ethanamide. How can ethanamide be converted into the nitrile you have named in b)? (iii) What type of reaction is this? c) Amides, like esters, can be hydrolysed in either acidic or alkaline solution. These reactions can be used in the laboratory to detect the presence of an amide, as illustrated for ethanamide by Scheme B. Scheme B CONH 2 Boil with H 2 SO 4 (aq) Boil with NaOH(aq) Solution A Solution B + Gas C Solution A smells of vinegar, and gas C, which has a characteristic smell, turns moist red litmus paper blue. Identify the smelly compound in Solution A, the compound in Solution B, and also gas C. Smelly compound in Solution A... [1] Compound in Solution B... [1] Gas C... [1] O H d) All amides contain the following group of atoms : C N This group forms a link in various long chain molecules. What name is given to this link? Name a synthetic polymer containing this link. (iii) What type of natural polymer contains this link? TOTAL / 14

24 TOPIC 23 Questionsheet 22 AMINES a) Write an ionic equation to show why an aqueous solution of methylamine is alkaline. Use your equation to explain why, on adding NaOH(aq), the fishy, ammoniacal smell of methylamine is intensified. b) Although phenylamine is almost insoluble in water, it dissolves readily in dilute hydrochloric acid to give a colourless solution of compound A. On neutralising this solution with aqueous sodium hydroxide, a colourless, oily liquid, B is formed. Name compounds A and B, and write equations for the two reactions. Name of A... [1] Name of B... [1] Equation 1... [1] Equation 2... [1] c) State whether ethylamine, and phenylamine is a weaker or stronger base than ammonia, and give reasons for your answers in both cases. Ethylamine Strength compared with ammonia... [1] Reasons [3] Phenylamine Strength compared with ammonia... [1] Reasons [3] d) The acylation of amines is useful in their identification. The product is purified by recrystallisation, after which its melting point is determined and compared with published values in a data book. What is meant by the term acylation? Name a suitable acylating agent. (iii) What type of compound is the product? (iv) Write an equation to show phenylamine reacting with the reagent you have chosen in d). TOTAL / 20

25 TOPIC 23 Questionsheet 23 DIAZOTISATION a) What is the meaning of the term diazotisation? Name the compounds you would use in the laboratory for the diazotisation of phenylamine. Also name the product, and write the equation for the reaction. Compound needed for diazotisation... [2] Name of product... [1] Equation... [1] (iii) Give the optimum temperature (or temperature range) for the diazotisation of phenylamine, and state the problems that would be encountered if the temperature were too high or too low. Optimum temperature... [1] Problem if the temperature were too high [2] Problem if the temperature were too low... [1] b) How does the product from a) react with 2-naphthol (β-naphthol)? Give the conditions, state what you would observe as a result of this reaction, and write an equation. Conditions... [2] Observation... [1] Equation [2] What name is given to the type of reaction in b)? c) How would the type of reaction in b) help you to distinguish between the following compounds? NH 2 NH 2 A B TOTAL / 17

26 TOPIC 23 Questionsheet 24 AMINO ACIDS a) Naturally occurring amino acids are described as α-amino acids. Write down the general formula of an α-amino acid. b) Glycine, H 2 N COOH, and glycollic acid, HO COOH, have very similar relative molecular masses, yet the melting point of glycine (232 C) is much higher than that of glycollic acid (79 C). How can you explain this?... [4] c) Experiments on electrophoresis, i.e. the movement of charged particles in an electric field, show that, in aqueous solution at low ph, amino acid particles migrate to the negative electrode, while at high ph they move to the positive electrode. Write ionic equations to show the formation of particles responsible for electrophoresis at low and high ph values. Equation (low ph)... [1] Equation (high ph)... [1] At an intermediate ph, there is no electrophoretic movement. Why? d) OH H 2 N CH COOH H 2 N CH COOH Alanine Serine The two amino acids alanine and serine, shown above, can combine together by an enzyme catalysed reaction to form one of two dipeptides; compounds which are essentially amides. Write equations to show the formation of two different dipeptides from alanine and serine. [2] Although the two dipeptides in d) are amino acids, they are not α-amino acids. Explain this statement. TOTAL / 13

27 TOPIC 23 Questionsheet 25 PROTEINS a) Proteins and polypeptides are natural polymers derived from α-amino acid molecules. Give the name and formula of the link between the amino acid molecules. Name... [1] Formula... [1] What type of polymerisation is involved? (iii) Explain why it is that the same combination of amino acids can give rise to different proteins or polypeptides. (iv) Give one difference between a protein and a polypeptide. b) State two ways in which the structure of a protein depends on hydrogen bonding [2] c) To identify its constituent amino acids, a protein must first be broken down into those amino acids. How can this be achieved in the laboratory? Suggest a method by which the individual amino acids could then be separated and identified. d) Insulin, used in the treatment of diabetes, is a peptide which is taken by injection through the skin. Why cannot medicines, of which the active ingredient is a peptide, be taken by mouth? TOTAL / 13

28 TOPIC 23 Questionsheet 26 TEST QUESTION 1 CARBONYL COMPOUNDS Below is the skeletal formula of testosterone. OH O a) What is its molecular formula? b) State what you would expect to see when it is treated with the following reagents: Brady s reagent (2,4-dinitrophenylhydrazine) Heating under reflux with acidified potassium dichromate(vi) (iii) Aqueous bromine c) Draw the skeletal formula of the compound that you would expect to be formed when testosterone is treated with either aqueous sodium borohydride or lithium aluminium hydride in dry ether. d) Draw the skeletal formula of the compound that you would expect to be formed when testosterone is heated under reflux with acidified potassium dichromate(vi) [2] [2] TOTAL (Continued...) /

29 TOPIC 23 Questionsheet 26 Continued TEST QUESTION 1 CARBONYL COMPOUNDS e) Z-hex-3-enal (cis-hex-3-enal), whose skeletal formula is shown below, is the smell of newly cut grass. O Draw the skeletal formula of the product you would expect to be produced when it is heated under reflux with acidified potassium dichromate(vi). f) The skeletal formulae of three other compounds are labelled A- C below. [2] O O O A B C Which of the above compounds is a stereoisomer of Z-hex-3-enal? Which of the above compounds is a structural isomer of Z-hex-3-enal? TOTAL / 12

30 TOPIC 23 Questionsheet 27 TEST QUESTION 1I PHENOLS Quinizarin is currently used as a marker in low taxed fuel, which can only be used for purposes such as agricultural tractors. Customs and Excise can test fuels by adding aqueous sodium hydroxide. If a purple colour appears in the sodium hydroxide solution, the quinizarin was in the fuel and therefore only a low tax was paid. a) Other than phenol, what functional group is present in quinizarin? O OH O OH Quinizarin b) What is the molecular formula of quinizarin? c) What is the empirical formula of quinizarin? d) Draw the structural formula of the product of the reaction of quinizarin with excess sodium hydroxide. Why does this compound dissolve in water, whilst quinizarin dissolves in the hydrocarbon fuel? [2] e) Draw the structural formula that you would expect when the compound is treated with excess bromine dissolved in an inert solvent. H O CH [2] TOTAL / 11