CHEMISTRY PAPER II: ORGANIC
SECTION A: Answer ALL questions in this Section.
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The main constituents of antifreeze has the structure [ethylene glycol structure shown]
What is its (a) IUPAC nomenclature (b) Molecular formula (c) Empirical formula (5 marks) -
Write equations for the elimination reactions which occur when (5 marks)
(a) butan-2-ol is dehydrated by passing over a heated catalyst
(b) 1-chloropropane reacts with a hot solution of potassium hydroxide in ethanol -
(a) Why is octane number rating important in petrol use in combustion engines?
(b) Give three (3) methods used to increase the octane number of petrol. (5 marks) -
(a) State three (3) properties of polyethene which make it particularly suitable for making plastic bags.
(b) State two (2) properties of polychloroethene (PVC), which is particularly suitable for making guttering and window frames. (5 marks) -
List five (5) industrial uses of phenol. (5 marks)
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(a) Give one (1) example each of a natural diol, a natural triol and an aromatic alkanol.
(b) In the fermentation of starch to ethanol, what are the two (2) enzymes of yeast used in the process? (5 marks) -
List five (5) classes of organic homologues that have the C=O functionality. (5 marks)
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Give the name and structures of the three (3) primary products of the ethylene-based petrochemical feed stock. (5 marks)
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List the three (3) main reactions that occur in the catalytic reforming of low-quality straight chain gasoline to high-quality gasoline. (5 marks)
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(a) Give the general formula of the alkynes and write the molecular formula of the first two members of the alkyne series. (3 marks)
(b) Draw the structures of the positional isomers of butyne. (2 marks)
SECTION B: Attempt Any TWO (2) Questions in this Section
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(a) Give the structure and IUPAC name of the three (3) isomers of
(i) C₄H₁₀O
(ii) C₃H₈O (12 marks)
(b) Enumerate three (3) general methods of preparation of alkenes and illustrate each method with a representative chemical equation. (9 marks)
(c) Write chemical equation for these reactions of glucose.
(i) Fermentation with zymase in yeast
(ii) Oxidation with atmospheric oxygen (4 marks) -
(a) Enumerate three (3) general methods of preparation of alkanamine and illustrate each method with a representative chemical equation. (9 marks)
(b) What is the molecular structure and name of the products of these reactions?
(i) Hydrolysis of ethyl propanoate
(ii) Reduction of methyl butanoate
(iii) Ammonolysis of propyl ethanoate (12 marks)
(c) Indicate which of the following compounds can exhibit any one or more of these types of isomerism - "positional", "functional", "metamerism", "tautomerism", "geometrical" or "optical".
(i) Methoxypropane
(ii) 2-chloropentane
(iii) Propanone (4 marks) -
(a) Use the compound whose structure is given below to answer the following questions: [structure of H₃CH₂C–C=C–CH₂OH with H atoms shown]
(i) Write the molecular and empirical formula of the compound
(ii) Give the IUPAC name of the compound
(iii) State the functional group(s) present in the compound
(iv) Name and give the molecular formula of the product formed from the reaction of the compound with hydrogen gas and nickel catalyst
(v) Give the structure and name of the two (2) stable positional isomers of the compound
(vi) Write the structure and name of one (1) stable structural isomer with different functional group of the compound. (20 marks)
(b) For the reactions of hydrogen bromide with but-1-ene:
(i) draw the structure of the two (2) possible carbocation intermediates
(ii) explain which carbocation is the more stable
(iii) Give the formula and name of the major product. (5 marks)
- (a) Consider the following reaction scheme. [reaction scheme shown with X, Y, Z, P intermediates]
(I) Give the reagent(s) for Reaction 1 and name the type of reaction involved.
(II) (i) Give the reagent(s) and conditions for Reaction 2.
(ii) Write an equation for this reaction using the symbol [O] to represent the oxidising agent.
(III) Give the reagent(s) and name the mechanism involved in Reaction 3.
(IV) Reaction 3 produces a mixture of two stereoisomers.
(i) What is the relationship between these two isomers?
(ii) How can the separate samples of these isomers be distinguished?
(V) (i) Draw the structure and state the name of the organic product formed when Y reacts with Z.
(ii) Draw the structure of an isomer of Z which forms ethanol on hydrolysis.
(VI) Write an equation for the complete combustion of X.
(VII) Give the general name and IUPAC nomenclature of P. (20 marks)
(b) Use the following data to show the stability of benzene relative to the hypothetical cyclohexa-1,3,5-triene.
[cyclohexene + H₂ → cyclohexane ΔH° = −120 kJ mol⁻¹]
[benzene + 3H₂ → cyclohexane ΔH° = −208 kJ mol⁻¹]
Give a reason for this difference in stability. (5 marks)
Question 1
The compound shown is ethane-1,2-diol (antifreeze/ethylene glycol): HO-CH₂-CH₂-OH
(a) IUPAC Nomenclature: Ethane-1,2-diol
(b) Molecular Formula: C₂H₆O₂
(c) Empirical Formula: CH₃O
Question 2
(a) Dehydration of butan-2-ol over heated catalyst (Al₂O₃):
CH₃CH(OH)CH₂CH₃ → CH₃CH=CHCH₃ + H₂O (major: but-2-ene)
Also: CH₂=CHCH₂CH₃ (minor: but-1-ene)
(b) 1-chloropropane + hot KOH(ethanol):
CH₃CH₂CH₂Cl + KOH(alc) → CH₃CH=CH₂ + KCl + H₂O
Question 3
(a) Why octane number rating is important:
Octane number measures a fuel's resistance to knocking (pre-ignition). High-compression engines require high-octane fuel to prevent knocking/pinging, which reduces engine efficiency and can cause damage.
(b) Three methods to increase octane number:
- Catalytic reforming (converting straight-chain to branched/aromatic hydrocarbons)
- Adding anti-knock agents (e.g., MTBE or ethanol blending)
- Catalytic cracking followed by alkylation/isomerisation
Question 4
(a) Three properties of polyethene suitable for plastic bags:
- Lightweight and flexible
- Chemically inert (resistant to most chemicals)
- Cheap to produce and easily moulded
(b) Two properties of PVC suitable for guttering and window frames:
- Rigid and hard (when unplasticised)
- Weather-resistant and durable (resistant to moisture and UV)
Question 5 — Five industrial uses of phenol:
- Manufacture of Bakelite (phenol-formaldehyde resin/plastic)
- Production of antiseptics and disinfectants
- Manufacture of nylon (via caprolactam)
- Production of aspirin (salicylic acid intermediate)
- Manufacture of explosives (e.g., picric acid)
Question 6
(a) Examples:
- Natural diol: Ethane-1,2-diol (ethylene glycol)
- Natural triol: Propane-1,2,3-triol (glycerol)
- Aromatic alkanol: Phenol (C₆H₅OH)
(b) Two enzymes used in fermentation of starch to ethanol:
- Amylase — converts starch to maltose/glucose
- Zymase — converts glucose to ethanol and CO₂
Question 7 — Five classes of organic homologues with C=O functionality:
- Aldehydes (–CHO)
- Ketones (C=O between two carbons)
- Carboxylic acids (–COOH)
- Esters (–COOC–)
- Amides (–CONH₂)
Question 8 — Three primary products of ethylene-based petrochemical feedstock:
| Product | Structure |
|---|---|
| Polyethene | –(CH₂–CH₂)ₙ– |
| Ethanol | CH₃CH₂OH |
| Ethanoic acid | CH₃COOH |
Question 9 — Three main reactions in catalytic reforming:
- Dehydrogenation — conversion of cyclohexane to benzene (aromatisation)
- Isomerisation — straight-chain → branched-chain alkanes
- Dehydrocyclisation — straight-chain alkanes → aromatic compounds (cyclisation + dehydrogenation)
Question 10
(a) General formula of alkynes: CₙH₂ₙ₋₂
- First member: C₂H₂ (ethyne/acetylene)
- Second member: C₃H₄ (propyne)
(b) Positional isomers of butyne (C₄H₆):
- But-1-yne: CH≡C–CH₂–CH₃
- But-2-yne: CH₃–C≡C–CH₃
SECTION B — Attempt Any TWO Questions
Question 11
(a)(i) Three isomers of C₄H₁₀O (ethers and alcohols):
| Structure | IUPAC Name |
|---|---|
| CH₃CH₂CH₂CH₂OH | Butan-1-ol |
| CH₃CH₂CH(OH)CH₃ | Butan-2-ol |
| CH₃OCH₂CH₂CH₃ | 1-methoxypropane |
(a)(ii) Three isomers of C₃H₈O:
| Structure | IUPAC Name |
|---|---|
| CH₃CH₂CH₂OH | Propan-1-ol |
| CH₃CH(OH)CH₃ | Propan-2-ol |
| CH₃OCH₂CH₃ | Methoxyethane |
(b) Three general methods of preparation of alkenes:
- Dehydration of alcohols (heated Al₂O₃ catalyst):
CH₃CH₂OH → CH₂=CH₂ + H₂O
- Dehydrohalogenation of haloalkanes (hot alcoholic KOH):
CH₃CH₂Br + KOH(alc) → CH₂=CH₂ + KBr + H₂O
- Cracking of large alkanes (high temp/catalyst):
C₁₀H₂₂ → C₅H₁₂ + C₅H₁₀ (pentane + pentene)
(c) Chemical equations for glucose reactions:
(i) Fermentation with zymase in yeast:
C₆H₁₂O₆ →(zymase)→ 2C₂H₅OH + 2CO₂
(ii) Oxidation with atmospheric oxygen:
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O
Question 12
(a) Three methods of preparation of alkanamines:
- Reduction of nitriles (using LiAlH₄):
CH₃CN + 4[H] → CH₃CH₂NH₂ (ethanamine)
- Reduction of nitroalkanes (using Sn/HCl then NaOH):
CH₃NO₂ + 6[H] → CH₃NH₂ + 2H₂O
- Ammonolysis of haloalkanes (reaction with excess NH₃):
CH₃Br + 2NH₃ → CH₃NH₂ + NH₄Br
(b) Products of reactions:
(i) Hydrolysis of ethyl propanoate:
CH₃CH₂COOC₂H₅ + H₂O → CH₃CH₂COOH + C₂H₅OH
Products: Propanoic acid (C₃H₆O₂) + Ethanol (C₂H₆O)
(ii) Reduction of methyl butanoate:
CH₃CH₂CH₂COOCH₃ + 4[H] → CH₃CH₂CH₂CH₂OH + CH₃OH
Products: Butan-1-ol (C₄H₁₀O) + Methanol (CH₄O)
(iii) Ammonolysis of propyl ethanoate:
CH₃COOC₃H₇ + NH₃ → CH₃CONH₂ + C₃H₇OH
Products: Ethanamide (C₂H₅NO) + Propan-1-ol (C₃H₈O)
(c) Types of isomerism:
| Compound | Types of Isomerism |
|---|---|
| (i) Methoxypropane | Functional group (isomeric with butanols), chain |
| (ii) 2-Chloropentane | Positional, optical (chiral centre at C-2) |
| (iii) Propanone | Functional group (isomeric with propanal), tautomerism |
Question 13
The compound shown: H₃CH₂C–C=C(H)–CH₂OH (but-2-en-1-ol with ethyl group → pent-2-en-1-ol)
Structural formula: CH₃CH₂–CH=CH–CH₂OH (pent-2-en-1-ol)
(i) Molecular formula: C₅H₁₀O
Empirical formula: C₅H₁₀O (simplest ratio same)
(ii) IUPAC name: Pent-2-en-1-ol
(iii) Functional groups present:
- Carbon-carbon double bond (C=C) — alkene
- Hydroxyl group (–OH) — alcohol
(iv) Product with H₂/Ni catalyst (hydrogenation of C=C):
CH₃CH₂CH₂CH₂CH₂OH
Pentan-1-ol, molecular formula: C₅H₁₂O
Question 14
(a) Reaction Scheme Analysis:
X = CH₃CH₂CHO (propanal) — aldehyde
Y = CH₃CH₂CH₂OH (propan-1-ol)
Z = CH₃CH₂COOH (propanoic acid)
P = CH₃CH₂C(OH)(CN)H — 2-hydroxybutanenitrile
(I) Reagents for Reaction 1 & type:
- Reagent: LiAlH₄ (or NaBH₄) in dry ether, or H₂/Ni
- Type: Reduction
(II)(i) Reagents and conditions for Reaction 2:
- Reagent: K₂Cr₂O₇/H₂SO₄ (acidified potassium dichromate), heat under reflux
(ii) Equation using [O]:
CH₃CH₂CH₂OH + 2[O] → CH₃CH₂COOH + H₂O
(III) Reagent and mechanism for Reaction 3:
- Reagent: HCN (hydrogen cyanide) with trace KCN catalyst
- Mechanism: Nucleophilic addition
(IV) Reaction 3 produces two stereoisomers:
(i) Relationship: They are enantiomers (non-superimposable mirror images; the product has a chiral/asymmetric carbon)
(ii) How to distinguish: Using plane-polarised light — each enantiomer rotates polarised light in opposite directions (one is (+), the other is (−)). A polarimeter is used.
(V)(i) Product when Y reacts with Z:
Y = propan-1-ol, Z = propanoic acid → Esterification
Product: Propyl propanoate (CH₃CH₂COOCH₂CH₂CH₃)
Structure:
CH₃CH₂–C(=O)–O–CH₂CH₂CH₃
(ii) Isomer of Z that forms ethanol on hydrolysis:
Z = propanoic acid (C₃H₆O₂). An isomer would be an ester that hydrolyses to give ethanol:
Methyl ethanoate (CH₃COOCH₃) — No; that gives methanol.
Ethyl methanoate: HCOOC₂H₅ → HCOOH + C₂H₅OH ✓
Structure: HCOOC₂H₅ (ethyl methanoate)
(VI) Complete combustion of X (propanal, CH₃CH₂CHO):
2CH₃CH₂CHO + 7O₂ → 6CO₂ + 6H₂O
(VII) General name and IUPAC name of P:
P = CH₃CH₂CH(OH)CN
- General name: Hydroxynitrile (cyanohydrin)
- IUPAC name: 2-Hydroxybutanenitrile
(b) Stability of benzene vs cyclohexa-1,3,5-triene:
From the data:
- Cyclohexene + H₂ → ΔH° = −120 kJ/mol
- Benzene + 3H₂ → ΔH° = −208 kJ/mol
Expected enthalpy for 3 double bonds = 3 × (−120) = −360 kJ/mol
Actual enthalpy = −208 kJ/mol
Difference (delocalisation energy/resonance stabilisation) = 360 − 208 = +152 kJ/mol
Reason: Benzene is more stable than the hypothetical cyclohexa-1,3,5-triene because its π electrons are fully delocalised over all six carbon atoms, forming a stable aromatic ring. This delocalisation lowers the energy of benzene by ~152 kJ/mol compared to a structure with three isolated double bonds. This extra stability is called the resonance/delocalisation energy.