Organic Chemistry

(12)2, 4

Chlorogenic acid occurs naturally in coffee and an edible species of bamboo.

The chlorogenic acid molecule contains a saturated ring, an aromatic ring and an alkene group.

a) [6]i. Identify as fully as you can the other functional groups present in chlorogenic

acid.

ii. How many chiral carbon atoms are there in a molecule of chlorogenic acid?

b) When chlorogenic acid is reacted under suitable conditions with NaOH(aq), followed by acidification, two crystalline solids may be obtained, one non-aromatic and one aromatic.Draw the displayed formula of each of these compounds. [2]

c) Draw the structural formula of the compound formed when the aromatic compound R you have drawn in part (b) is added to an excess of Br2 dissolved in an organic solvent. [2]

d) When the aromatic compound R is reacted with an excess of NaHCO3(aq), compound S is formed which has the molecular formula C9H7O4Na. [3]

i. Suggest the structural formula of S.

ii. Suggest why this product contains only one Na atom/ion although the NaHCO3 is in excess.

(12)2, 5

Lactic acid (2-hydroxypropanoic acid), CH3CH(OH)CO2H, is present in milk.

Lactic acid can also be produced in the laboratory from ethanol, CH3CHO, by the following reactions.

a) [5]i. Name the reagent and conditions used and the type of reaction that occurs in

step 1.

ii. Describe the mechanism of this reaction. In your answer you should show all charges and lone pairs and show the movement of electrons by curly arrows.

Lactic acid present in milk rotates the plane of polarised light.

Lactic acid produced in a laboratory by the reactions above does not rotate the plane of polarised light.

b) [4]i. What feature of the lactic acid present in milk causes the rotation of the plane

of polarised light?

ii. Suggest, in terms of the mechanism of step 1 in the above reaction scheme, and the shape of the CH3CHO molecule, why synthetic lactic acid does not rotate the plane of polarised light.

The effect of plane polarised light on tartaric acid (2,3-dihydroxybutanedioic acid), HO2CCH(OH)CH(OH)CO2H was investigated by Loius Pasteur.

Pasteur identified three different types of tartaric acid molecule.

Molecule A rotated plane polarised light to the rightMolecule B rotated plane polarised light to the leftMolecule C had no effect on plane polarised light

c) Suggest an explanation for these observations. [3]

(12)3, 4

d) Ionic charges are important in determining the 3-dimensional structure of the haemoglobin molecule. The four protein chains of deoxyhaemoglobin are held in position by 8 ionic ‘salt’ links. Some of these interactions are between the C-terminal end of one chain and the N-terminal end of another chain, whereas other interactions are between aspartic acid residues on one chain and arginine residues on another chain. [5]

i. Using the tetrapeptide whose structure is given below, and taking account of the ionic forms that the amino acid residues exist in at pH7, draw the structures of two of these tetrapeptide chains to illustrate both of the ionic interactions mentioned above.

ii. Describe two further ways, other than ionic linkages, by which the tertiary structures of proteins can be stabilised.

Glycine Arginine Aspartic Glycine acid

e) The antibiotic valinomycin acts by allowing the uncontrolled movement of ions across cell membranes. Valinomcin is a cyclic compound containing six amino acid and six hydroxyacid residues. [3]

i. Apart from the peptide group, what other fuctional group is present in the valinomycin molecule?

When treated with a peptide enzyme, the peptide bonds in the ring of valinomycin are hydrolysed. Only two products are formed.

ii. Draw the structural formulae of the two compounds produced.

(12)3, 5

Malic acid occurs in green apples and grapes. It is often added to beverages and confectionery to confer a sour taste.

a) Suggest the reagents and conditions you would use in a three-step synthesis of malic acid from bromoethanal, identifying the intermediates G and H. [5]

b) Malic acid can be dehydrated to give a mixture of two isomeric alkenedioic acids with the molecular formula C4H4O4. [6]

i. Draw the structures of the isomers, and state the type of isomerism they show.

ii. Suggest reagents and conditions for the dehydration reaction.

iii. The pKa values of the two acidic groups in one isomer, J, are 3.0 and 4.4, whereas in the other isomer, K, they are 1.9 and 6.2.

Use the pKa values to suggest which isomer, J or K, produces the more stable mono-anion on treatment with 1mol of NaOH? Explain your answer.

iv. Draw the displayed formula of the mono-anion produced in (iii), and use your formula to suggest an explanation for why it is more stable than the mono-anion of the other isomer.

Gently heating the anhydrous crystals of one of the isomers J or K produces a neutral compound L, C4H2O3, which does not react with sodium metal or give a precipitate with 2,4-dinitrophenylhydrazine.

Compound L reacts with ammonia to give a compound M, C4H5NO3, which gives a salt on reaction with NaOH but not with HCl. Compound M decolourises Br2(aq).

c) Suggest structures for compounds L and M, and identify which isomer, J or K, produces L. Write equations for all reactions, and explain the observations. [6]

When malic acid is heated with acidified K2Cr2O7, compound N is formed. Heating N in an inert solvent for several hours produces P, C3H4O3 and a gas Q. Both N and P react with 2,4-dinitrophenylhydrazine. Compound P also gives a yellow precipitate with aqueous alkaline iodine.

d) Suggest structures for N and P, and use the information given to suggest the identity of gas Q. [3]

(11)2, 5

Compound K has the molecular formula C4H8O2.

K decolourises aqueous bromine.

When 0.10mol of K is reacted with an excess of sodium metal, 2.4dm3 of hydrogen are formed, measured at room temperature and pressure.

a) Use all of the above information to determine the identity and number of each of the functional groups present in compound K.For each functional group you identity, explain how you came to your decision. [5]

i. Reaction with aqueous bromine.

ii. Reaction with sodium metal.

b) Draw the displayed formulae of all the possible stereoisomers of K which have the following features

They have molecular formula C4H8O2 and give the reactions stated earlier. No oxygen atom is attached to any carbon atom which is involved in a double

bond. No carbon atom has more than one oxygen atom joined to it.

For each structure you draw, state the type of stereoisomerism it shows and give one further piece of relevant information about it.

You are not required to label functional groups. [7]

(11)2, 6

Compound W has the molecular formula C7H7OCl. It is an aromatic compound which contains two functional groups.

Data about the reactions of W are given in the table.

reaction reagent result

1 AgNO3(aq), warmWhite solid formed which is soluble in an excess of NH3(aq)

2 Br2(aq) in an excess White solid formed which has Mr = 379.2

3MnO4

-/OH- heat under reflux then acidify

MnO4- is decolourised;

One organic product formed with Mr = 138

4 NaColourless gas evolved;White solid formed which is soluble in H2O

5NaOH(aq) at room temperature

Colourless solution formed

In this question, when identifying functional groups, your answers should be unambiguous.

a) [5]i. What is the white solid that is formed in reaction 1?

ii. Name the functional group that reaction 1 shows to be present in W.

iii. Based only on reaction 4, give the names of two different functional groups that could be present in W.

iv. Which of the functional groups you have named in (iii) is confirmed by reaction 5? Explain your answer.

b) Deduce the molecular formula of the organic product formed in reaction 3. [1]

c) [6]i. Deduce the molecular formula of the white solid formed in reaction 2.

ii. What type of reaction takes place in reaction 2?

iii. Explain clearly how the formation of this compound shows that compound W

is an aromatic compound rather than an aliphatic compound.

iv. Name the functional group present in W that is confirmed by reaction 2.

v. Which other reaction confirms that W is aromatic? Explain your answer.

d) You now have enough information to determine the structural formula of W. [4]

i. Draw the fully displayed structure of W.

ii. Explain clearly why you have placed each of the two functional groups in their particular positions.

(11)3, 2

c) Heating malonic acid (HO2CCH2CO2H) with P4O10 at 140°C produces an easily-liquefied gas F which has a boiling point of 7°C and has the molecular formula C3O2. [4]

i. Suggest a structure for F and describe its shape.

ii. The addition of water to F re-forms malonic acid. Suggest the product of the reaction of F with each of the following.

NH3(g) HCl(g)

d) Suggest synthetic routes to the following dicarboxylic acids starting from 1,2-dibromoethane. [4]

(10)2, 5

Animal skin and bone contains the protein collagen.Gelatin, which is used in the food and pharmaceutical industries, is another protein which may be obtained from collagen.

The structure of a portion of the gelatin molecule is shown below. This portion contains a number of amino acids and imino acids. The latter are related to amino acids but contain the >NH group instead of the –NH2 group. In this question we will refer to both sorts of acid as ‘amino acid’.

Gelatin is prepared by the denaturation of collagen.

a) [2]i. What is meant by the term denaturation?

ii. Suggest a brief outline of one method by which collagen may be denatured to

produce gelatin.

b) How many different amino acid residues are present in this portion of the gelatin molecule? [1]

c) Two of these amino acid residues are present more than once in this portion. [5]

i. Draw a displayed formula for each of these amino acids.

ii. One of the amino acid residues present in this portion of the gelatin molecule contains more than one chiral atom.Draw the displayed formula of this amino acid and indicate each chrial atom with an asterisk (*).

Skin is a very tough, flexible and waterproof substance which is easily pierced by sharp objects.

Kevlar® is an aromatic polyamide which is used in stab-proof vests and also in high quality bicycle tyres.

Proteins and Kevlar® may be hydrolysed in a similar manner.

d) [5]i. How could proteins by hydrolysed in the laboratory to form a mixture of their

constituent amino acids?

ii. What compounds will be produced when Kevlar® is hydrolysed?Give their structural formulae.

iii. Proteins and Kevlar® are polyamides.What is the essential difference between their monomers?

Sutures are the stiches that surgeons use to hold skin, internal organs, blood vessels and other tissues of the human body together after they have been severed by injury or surgery.

‘Soluble stiches’ which are used within the body may be made by reacting together glycolic acid, HOCH2CO2H, and lactic acid, CH3CH(OH)CO2H.

e) When one molecule of glycolic acid reacts with one molecule of lactic acid, it is possible to form two esters with different structural formulae.

Draw the structural formula of each of these esters. [2]

In the material used for ‘soluble stiches’, many molecules of each acid have been reacted to form a long chain ‘polyester’ molecule which contains many ester groups.This polyester material may be used in surgery to sew up wounds inside the body.Over a period of time the polyester undergoes a chemical reaction and breaks up to re-form the two individual hydroxyacids.

f) [2]i. Suggest what type of chemical reaction causes the polyester material to break

up over a period of time.

ii. Suggest why the products of this reaction are soluble in water.

(10)3, 1

a) [5]i. Explain what is meant by the term entropy of a chemical system.

ii. Describe and explain how the entropy of each of the following systems will change during the stated process. Assume the pressure of each system remains at 1atm throughout.

1mol of Cl2(g) at 298K is added to 1mol of N2(g) at 298K. 1mol of Cl2(g) at 298K is heated to 373K.

1mol of Cl2(g) at 298K is reacted with iodine according to the following equation.

C l2 (g )+13

I2(s)→23

IC l3(l)

1mol of Cl2(g) at 1000K is photolysed according to the following equation.

C l2(g)→ 2 Cl ∙

b) [2]i. Describe how the reaction of hydrogen with chlorine differs from that of

hydrogen with bromine.

ii. How would you expect the reaction of hydrogen with fluorine to differ from that of hydrogen with chlorine?

c) Chloroalkanes and bromoalkanes can be made by the reaction of the corresponding halogen with alkanes, for example: [6]

C2 H 6+C l2 →C2 H 5 Cl+ HCl

i. State the conditions needed for this reaction.

ii. Name and describe the mechanism of this reaction.

iii. Suggest why it is not possible to make iodoalkanes by this method.

d) Suggest a structural formula for each of the compounds A – D in the following schemes. [4]

e) Chlorofluoralkanes, CFCs, were once used as refrigerant fluids and aerosol propellants. In many applications they have now been replaced by alkanes. This is because CFCs contribute to the destruction of the ozone layer. [3]

i. Suggest one reason why CFCs were originally used for these purposes.

ii. Explain how CFCs destroy the ozone layer.

iii. Suggest one potential hazard of using alkanes instead of CFCs.

(10)3, 2

The soy bean, Glycine max, is a legume native to East Asia. It was first cultivated in China over 5000 years ago.The beans have many culinary uses, including soy oil, soy sauce, soy milk, dofu and TVP (textured vegetable protein made from soy flour).

a) Soy sauce is produced by the fermentation of soy beans by the mould Aspergillus oryzae. The distinctive salty taste of the sauce is due to salts of glutamic acid formed during fermentation. [6]

i. Explain what is meant by the term pKa as applied to a weak acid HA.

There are three pKa values associated with glutamic acid: 2.1, 4.1 and 9.5.

ii. Make use of these pKa values to suggest the major species present in solutions of glutamic acid with the following pH values.

pH 1 pH 3 pH 7 pH 11

b) Dofu is made by coagulating soy milk and then pressing the curds between fine cloth to extrude most of the moisture. Coagulating agents that have been used include certain salts, acids or enzymes. Coagulation is due to the denaturation of the proteins in the soy milk.

[You may find that including suitable sketches or diagrams will help you in your answers to parts (i), (ii) and (iii).] [8]

i. What aspect of a protein’s structure is altered during coagulation, and why does this occur?

The calcium salts CaSO4 and CaCl2 are often used to produce dofu.

ii. Suggest how Ca2+(aq) ions can interact with a protein to bring about denaturation.

iii. Suggest how a weak acid might interact with a protein to bring about denaturation.

The addition of glucono-delta-lactone, GDL, to soy milk produces a soft form of dofu due to a gradual acidification of the mixture. In aqueous solution the following equilibrium is slowly set up.

When 1.00g of GDL (Mr = 178) was dissolved in 50.0cm3 water and the solution allowed to reach equilibrium, the concentration of gluconic acid was found to be 0.0670moldm-3.

iv. Write an expression for Kc for the equilibrium above, and use the data given to calculate its value. You can assume that [H2O] = 55.5moldm-3 throughout.

c) Soy beans, and especially the dofu made from them, are a good source of dietary isoflavenoids, which are claimed to help in the prevention of some cancers. The major isoflavenoid in soy is diadzein. [6]

i. Draw the structural formula of the compound formed when diadzein reacts with an excess of Br2(aq).

When diadzein is treated with H2 and Ni, compound F, C15H14O4, is formed. One mole of compound F reacts with three moles of sodium metal. F also dissolves in NaOH(aq). F reacts with acidified K2Cr2O7 to give compound G, C15H12O4, which gives an orange precipitate with 2,4-dinitrophenylhydrazine reagent.

ii. Suggest a structural formula for F and for G, identifying any chiral carbon atoms. Explain the reactions which occur.

(10)3, 3

The direct oxidation of alcohols in a fuel cell represents potentially the most efficient method of obtaining useful energy from a renewable fuel.

c) [3]i. Use suitable bond energy values from the Data Booklet to calculate ΔH for the

combustion of one mole of ethanol according to C H 3 C H 2 OH+3 O2→ 2 C O2+3 H 2O. Use a value of 805kJmol-1 for the bond energy of each C=O bond in CO2.

ii. Suggest a reason for the difference between your calculated value and that given as -1367kJmol-1.

d) Alcohol J, CxHyOH, is a volatile fungal metabolite whose presence when detected in air can indicate hidden fungal attack on the timbers of a house.When 0.10cm3 of liquid J was dissolved in an inert solvent and an excess of sodium metal added, 10.9cm3 of gas (measured at 298K) was produced.When 0.10cm3 of liquid J was combusted in an excess of oxygen in an enclosed vessel, the volume of gas (measured at 298K) was reduced by 54.4cm3. The addition of an excess of NaOH(aq) caused a further reduction in gas volume of 109cm3 (measured at 298K). [8]

i. Use these data to calculate values for x and y in the molecular formula CxHyOH for J.

Alcohol J reacts with acidified K2Cr2O7, and can be dehydrated to alkene K. On treating K with an excess of hot acidified concentrated KMnO4, an equimolar mixture of ethanoic acid and propanone is produced.

ii. Use this information to deduce the structural formulae for J and K, explaining your reasoning.

iii. Suggest suitable reagents and conditions for the conversion of J and K.

iv. Explain whether K can show geometrical isomerism.

(10)3, 4g

Oxidation is an important reaction in organic chemistry. Both aldehydes and carboxylic acids can be prepared by the oxidation of alcohols with acidified K2Cr2O7. [5]

i. Describe how you could ensure that only either the aldehyde or the carboxylic acid is produced during the oxidation process.

ii. Compounds L and M, both C9H10, and compound N, C9H12O, are all oxidised by hot concentrated alkaline KMnO4, followed by acidification, to give benzene-1,2-dicarboxylic acid, P.

Compound L reacts with Br2(aq), but compound M does not.Compound N reacts with alkaline aqueous iodine.Suggest structures for compounds L, M and N.