1. The molecular formula C₆H₁₄ has five (5) structural isomers, name them. (5 marks)
2. (a) Give the names of the first three members of the cycloalkane series. (3 marks)
(b) Name two (2) general types of reactions of cycloalkanes. (2 marks)
3. Classify the following compounds as primary, secondary or tertiary haloalkanes: (5 marks)
(a) 2-iodopropane
(b) 2-chloro-2-methylpropane
© 1-chloro-2-methylpropane
(d) 3-bromopentane
(e) 1-bromobutane
4. Classify the following compounds as primary, secondary or tertiary alkanols: (5 marks)
(a) 2-butanol
(b) 2-methyl-2-propanol
© 2-methyl-1-propanol
(d) 3-pentanol
(e) 3-methyl-1-butanol
5. (a) What type of isomerism is likely to exist for a compound with molecular formula C₃H₆O? (5 marks)
(b) Give the name and structure of the isomers of C₃H₆O.
6. Name and give the molecular formula of functional derivatives of alkanoic acids. (5 marks)
7. (a) What classes of organic homologues are commonly required to produce an alkanoate?
(b) Give the names of the organic reagents required for the formation of these alkanoates:
(i) CH₃CH₂COOCH₂CH₃
(ii) CH₃COOCH₂CH₃ (5 marks)
8. Classify the following as primary, secondary or tertiary alkanamine: (5 marks)
(a) Trimethylamine
(b) 2-Aminopropane
© Dimethylamine
(d) Dimethyl Phenylamine
(e) 3-Aminopentane
9. (a) Give the molecular polysaccharides.
(b) Name two (2) naturally occurring disaccharides and two (2) polysaccharides. (5 marks)
10. (a) What is vulcanization?
(b) Name the monomer of natural rubber and state two (2) other monomers that have been employed for the production of synthetic rubber. (5 marks)
SECTION B
11. (a) Using equations to illustrate what is meant by the following terms: (10 marks)
(i) Saponification
(ii) Esterification
(iii) Ethanoylation
(iv) Decarboxylation
(v) Dehydration
(b) Give the name of the possible organic product(s) of the following transformations: (10 marks)
(i) Dehydration of 2-butanol
(ii) Hydration of ethyne
(iii) Hydrochlorination of propene
(iv) Hydroxylation of ethene
(v) Reduction of 2-chloropropane
© Draw displayed (structural) formulae for the following compounds: (5 marks)
(i) Butanoyl chloride
(ii) Ethanoic butanoic anhydride
(iii) Ethyl 2-hydroxypropanoate
(iv) N-methyl, N-ethyl, 2-aminobutane
(v) Sodium 2-hydroxyethanoate
12. (a) Give the structure of the product of the oxidation of these compounds: (6 marks)
(i) 1-Propanol
(ii) 2-Propanol
(iii) 2-Butanol
(b) Give the structure of the product of the Clemmensen’s reduction of these compounds: (4 marks)
(i) Propanal
(ii) Propanone
© Calculate the molecular formula of an organic compound with 59.95% carbon, 13.42% hydrogen and 26.63% oxygen; and whose vapour density is 30. (5 marks)
(d) List five (5) primary uses of fats and oils. (5 marks)
(e) Draw the repeating unit of the polymer formed by the reaction between butanedioic acid and hexane-1,6-diamine. State the type of polymerisation occurring in this reaction and give a name for the linkage between the monomer units in this polymer. (5 marks)
13. (a) Give the reagent(s) required to convert ethanoyl chloride to the following compounds: (10 marks)
(i) CH₃COOH
(ii) CH₃COOC₂H₅
(iii) CH₃CONH₂
(iv) CH₃COC₆H₅
(v) CH₃CO-O-OC-CH₃
(b) Indicate the structure of the compounds indicated by the symbols X and Y in this equation:
Propanoic acid + Cl₂/P (sunlight) → X; X + excess NH₃ → Y (4 marks)
© Indicate the structure of the compounds indicated by the symbols X, Y and Z in these equations:
- CH₃CHO + CH₃MgBr → H⁺ → X
- CH₃COCH₃ + CH₃MgBr → H⁺ → Y
- CH₃C≡N + CH₃MgBr → H⁺ → Z (6 marks)
(d) The amino acid R is shown below:
CH₃CH₂–C(NH₂)(H)–COOH
(i) Draw the structure of the zwitterion formed by R.
(ii) 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 (ii). (5 marks)
14. (a) There are several non-cyclic structural isomers with the molecular formula C₆H₁₂.
(i) One of these isomers, 2-methylpent-2-ene, (CH₃)₂C=CHCH₂CH₃, reacts with hydrogen bromide. Name the major product and account for its formation by reference to the mechanism of the reaction.
(ii) Identify one linear alkene of formula C₆H₁₂ which can exist as a pair of stereoisomers. State the type of stereoisomerism shown, name the alkene and draw the structures of the two isomers. (11 marks)
(b) Chloromethane can react with ammonia to produce a primary amine.
(i) What feature of the chloromethane molecule makes it susceptible to attack by an ammonia molecule?
(ii) Name the amine produced in this reaction.
(iii) Outline a mechanism for this reaction. (6 marks)
© Ethene and other important hydrocarbons can be produced industrially from decane, C₁₀H₂₂. Name the process involved. Write two equations for reactions in which ethene is formed from decane by this process. Explain the economic importance of the process. (8 marks)
#SECTION A SOLUTIONS
Q1 — Five structural isomers of C₆H₁₄
C₆H₁₄ is a hexane with general formula CₙH₂ₙ₊₂ (alkane). The five structural isomers are:
- Hexane — CH₃CH₂CH₂CH₂CH₂CH₃ (straight chain)
- 2-Methylpentane — CH₃CH(CH₃)CH₂CH₂CH₃
- 3-Methylpentane — CH₃CH₂CH(CH₃)CH₂CH₃
- 2,2-Dimethylbutane — CH₃C(CH₃)₂CH₂CH₃
- 2,3-Dimethylbutane — CH₃CH(CH₃)CH(CH₃)CH₃
Q2 — Cycloalkanes
(a) First three members:
- Cyclopropane (C₃H₆)
- Cyclobutane (C₄H₈)
- Cyclopentane (C₅H₁₀)
(b) Two general types of reactions of cycloalkanes:
- Substitution reactions (e.g., halogenation in UV light — like alkanes; for larger rings C₅ and above)
- Addition reactions (e.g., ring-opening addition — especially for smaller, strained rings like cyclopropane and cyclobutane)
Q3 — Classification of haloalkanes
A haloalkane is:
- Primary (1°): halogen on a carbon bonded to only one other carbon
- Secondary (2°): halogen on a carbon bonded to two other carbons
- Tertiary (3°): halogen on a carbon bonded to three other carbons
(a) 2-Iodopropane — CH₃CHI CH₃: I on C-2 which is bonded to 2 carbons → Secondary (2°)
(b) 2-Chloro-2-methylpropane — (CH₃)₃CCl: Cl on C bonded to 3 carbons → Tertiary (3°)
© 1-Chloro-2-methylpropane — ClCH₂CH(CH₃)₂: Cl on C-1 bonded to only 1 carbon → Primary (1°)
(d) 3-Bromopentane — CH₃CH₂CHBrCH₂CH₃: Br on C-3 bonded to 2 carbons → Secondary (2°)
(e) 1-Bromobutane — CH₃CH₂CH₂CH₂Br: Br on C-1 bonded to 1 carbon → Primary (1°)
Q4 — Classification of alkanols
- Primary (1°): –OH on a carbon bonded to one other carbon
- Secondary (2°): –OH on a carbon bonded to two other carbons
- Tertiary (3°): –OH on a carbon bonded to three other carbons
(a) 2-Butanol — CH₃CH(OH)CH₂CH₃: OH on C-2 bonded to 2 carbons → Secondary (2°)
(b) 2-Methyl-2-propanol — (CH₃)₃COH: OH on C bonded to 3 carbons → Tertiary (3°)
© 2-Methyl-1-propanol — (CH₃)₂CHCH₂OH: OH on C-1 bonded to 1 carbon → Primary (1°)
(d) 3-Pentanol — CH₃CH₂CH(OH)CH₂CH₃: OH on C-3 bonded to 2 carbons → Secondary (2°)
(e) 3-Methyl-1-butanol — (CH₃)₂CHCH₂CH₂OH: OH on terminal C-1 bonded to 1 carbon → Primary (1°)
Q5 — Isomerism of C₃H₆O
(a) Type of isomerism: C₃H₆O has degree of unsaturation = (2×3 + 2 − 6)/2 = 1, so it has one double bond or one ring. The isomers can be functional group isomers (aldehyde, ketone, cyclic ether, enol, epoxide) — specifically functional group isomerism and chain isomerism.
(b) Isomers of C₃H₆O:
-
Propanal (propionaldehyde)
CH₃CH₂CHO — an aldehyde -
Propanone (acetone)
CH₃COCH₃ — a ketone -
Methoxyethene (methyl vinyl ether)
CH₂=CH–O–CH₃ — a vinyl ether -
Oxetane (trimethylene oxide)
A 4-membered cyclic ether (ring) -
Allyl alcohol (prop-2-en-1-ol)
CH₂=CHCH₂OH — an alkenol
(The most commonly expected answers in IJMB context are propanal and propanone as the primary pair)
Q6 — Functional derivatives of alkanoic acids
Functional derivatives are compounds derived from carboxylic acids (RCOOH) by replacing the –OH group:
Name
Formula
Acid chloride (acyl chloride)
RCOCl
Acid anhydride
RCO–O–OCR
Ester
RCOOR’
Amide
RCONH₂
Nitrile (not direct derivative but related)
RCN
The four main functional derivatives:
- Acyl (acid) chloride — RCOCl e.g., CH₃COCl
- Acid anhydride — (RCO)₂O e.g., (CH₃CO)₂O
- Ester — RCOOR’ e.g., CH₃COOC₂H₅
- Amide — RCONH₂ e.g., CH₃CONH₂
Q7 — Production of alkanoates
(a) Classes of organic homologues required to produce an alkanoate (ester):
An alkanoate is formed from:
- An alkanol (alcohol) — provides the R’OH part
- An alkanoic acid (carboxylic acid) — provides the RCOOH part
(Reaction: RCOOH + R’OH ⇌ RCOOR’ + H₂O — esterification)
(b) Reagents:
(i) CH₃CH₂COOCH₂CH₃ (ethyl propanoate):
- Alkanoic acid: propanoic acid (CH₃CH₂COOH)
- Alkanol: ethanol (C₂H₅OH)
(ii) CH₃COOCH₂CH₃ (ethyl ethanoate):
- Alkanoic acid: ethanoic acid (CH₃COOH)
- Alkanol: ethanol (C₂H₅OH)
Q8 — Classification of alkananamines
- Primary (1°): N bonded to one carbon group
- Secondary (2°): N bonded to two carbon groups
- Tertiary (3°): N bonded to three carbon groups
(a) Trimethylamine — N(CH₃)₃: N bonded to three CH₃ groups → Tertiary (3°)
(b) 2-Aminopropane — CH₃CH(NH₂)CH₃: N bonded to one carbon group → Primary (1°)
© Dimethylamine — (CH₃)₂NH: N bonded to two CH₃ groups → Secondary (2°)
(d) Dimethyl Phenylamine — (CH₃)₂N–C₆H₅: N bonded to three carbon groups (2 methyl + 1 phenyl) → Tertiary (3°)
(e) 3-Aminopentane — CH₃CH₂CH(NH₂)CH₂CH₃: N bonded to one carbon group → Primary (1°)
Q9 — Polysaccharides
(a) Molecular polysaccharides:
Polysaccharides are complex carbohydrates formed by condensation polymerisation of many monosaccharide units (mainly glucose) joined by glycosidic bonds. Their general molecular formula is (C₆H₁₀O₅)ₙ.
(b) Two naturally occurring disaccharides and two polysaccharides:
Disaccharides:
- Sucrose (glucose + fructose) — table sugar
- Maltose (glucose + glucose) — malt sugar
(Also: lactose — glucose + galactose)
Polysaccharides:
- Starch — (C₆H₁₀O₅)ₙ, storage carbohydrate in plants
- Cellulose — (C₆H₁₀O₅)ₙ, structural carbohydrate in plant cell walls
Q10 — Vulcanization and rubber
(a) Vulcanization: Vulcanization is the process of treating natural rubber with sulphur (and heat) to introduce cross-links (sulphur bridges) between the polymer chains, making the rubber harder, more elastic, more durable, and resistant to temperature changes and solvents.
(b) Monomer of natural rubber and synthetic rubber monomers:
Monomer of natural rubber: Isoprene (2-methylbuta-1,3-diene) — CH₂=C(CH₃)–CH=CH₂
Two monomers used in synthetic rubber:
- Buta-1,3-diene (butadiene) — used to make polybutadiene rubber (Buna rubber)
- Chloroprene (2-chlorobuta-1,3-diene) — used to make neoprene rubber
(Also acceptable: styrene for SBR rubber)
SECTION B SOLUTIONS
Q11(a) — Illustrated definitions
(i) Saponification — alkaline hydrolysis of an ester to give an alcohol and a salt of a carboxylic acid:
CH₃COOC₂H₅ + NaOH → CH₃COONa + C₂H₅OH
(Ethyl ethanoate + sodium hydroxide → sodium ethanoate + ethanol)
(ii) Esterification — reaction between a carboxylic acid and an alcohol to form an ester and water:
CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O
(Ethanoic acid + ethanol ⇌ ethyl ethanoate + water)
(iii) Ethanoylation (acetylation) — introduction of an ethanoyl (CH₃CO–) group into a compound, typically using ethanoyl chloride or ethanoic anhydride:
C₂H₅OH + CH₃COCl → CH₃COOC₂H₅ + HCl
Or with amine: C₂H₅NH₂ + CH₃COCl → CH₃CONHC₂H₅ + HCl
(iv) Decarboxylation — loss of CO₂ from a carboxylic acid or its salt:
CH₃COONa + NaOH →(CaO, heat)→ CH₄ + Na₂CO₃
Or: RCOOH → R–H + CO₂
(v) Dehydration — removal of water from a molecule, typically from an alcohol to form an alkene:
C₂H₅OH →(conc. H₂SO₄, 170°C)→ CH₂=CH₂ + H₂O
Q11(b) — Organic products of transformations
(i) Dehydration of 2-butanol:
CH₃CH(OH)CH₂CH₃ →(conc. H₂SO₄, heat)→ CH₃CH=CHCH₃ + H₂O
Major product: but-2-ene (and minor but-1-ene)
By Zaitsev’s rule, but-2-ene is the major product.
(ii) Hydration of ethyne:
HC≡CH + H₂O →(H₂SO₄/HgSO₄ catalyst)→ CH₃CHO
Product: ethanal (acetaldehyde) — via Markovnikov addition, forms vinyl alcohol (enol) which tautomerises to ethanal.
(iii) Hydrochlorination of propene:
CH₃CH=CH₂ + HCl → CH₃CHClCH₃
By Markovnikov’s rule: H adds to CH₂ (less substituted C), Cl adds to CH (more substituted C).
Major product: 2-chloropropane
(iv) Hydroxylation of ethene:
CH₂=CH₂ + [O] + H₂O →(KMnO₄, cold dilute)→ CH₂(OH)–CH₂(OH)
Product: ethane-1,2-diol (ethylene glycol)
(v) Reduction of 2-chloropropane:
CH₃CHClCH₃ + 2[H] →(Zn/HCl or LiAlH₄)→ CH₃CH₂CH₃ + HCl
Product: propane
Q11© — Displayed structural formulae
(i) Butanoyl chloride:
O
‖
CH₃–CH₂–CH₂–C–Cl
(ii) Ethanoic butanoic anhydride (mixed anhydride):
O O
‖ ‖
CH₃–C–O–C–CH₂CH₂CH₃
(iii) Ethyl 2-hydroxypropanoate (ethyl lactate):
OH O
| ‖
CH₃–CH–C–O–CH₂CH₃
(iv) N-methyl, N-ethyl, 2-aminobutane:
CH₃
|
CH₃–CH₂–N
|
CH₂CH₃
|
(attached to C-2 of butane)
Full structure:
CH₃–CH(N(CH₃)(C₂H₅))–CH₂–CH₃
N is bonded to: methyl, ethyl, and the C-2 of butane chain.
(v) Sodium 2-hydroxyethanoate (sodium glycolate):
OH O
| ‖
HO–CH₂–C–O⁻Na⁺
i.e., HOCH₂COONa
Q12(a) — Oxidation products
(i) 1-Propanol (primary alcohol):
With mild oxidation (e.g., K₂Cr₂O₇/H₂SO₄):
CH₃CH₂CH₂OH → propanal (CH₃CH₂CHO) → with excess oxidant → propanoic acid (CH₃CH₂COOH)
Primary alcohol → aldehyde (mild) → carboxylic acid (excess)
(ii) 2-Propanol (secondary alcohol):
CH₃CH(OH)CH₃ → propanone (CH₃COCH₃)
Secondary alcohol → ketone only (cannot be further oxidised easily)
(iii) 2-Butanol (secondary alcohol):
CH₃CH(OH)CH₂CH₃ → butanone (CH₃COCH₂CH₃)
Secondary alcohol → ketone
Q12(b) — Clemmensen reduction
Clemmensen reduction (Zn amalgam/conc. HCl) reduces carbonyl compounds (aldehydes and ketones) to alkanes:
(i) Propanal:
CH₃CH₂CHO →(Zn(Hg)/HCl)→ CH₃CH₂CH₃ (propane)
(ii) Propanone:
CH₃COCH₃ →(Zn(Hg)/HCl)→ CH₃CH₂CH₃ (propane)
Q12© — Molecular formula from % composition
Given: C = 59.95%, H = 13.42%, O = 26.63%, vapour density = 30
Moles ratio:
- C: 59.95/12 = 4.996 ≈ 5
- H: 13.42/1 = 13.42 ≈ 13.4
- O: 26.63/16 = 1.664 ≈ 1.66
Divide by smallest (1.664):
- C: 4.996/1.664 = 3.00
- H: 13.42/1.664 = 8.07 ≈ 8
- O: 1.664/1.664 = 1.00
Empirical formula = C₃H₈O
Empirical formula mass = 3(12) + 8(1) + 16 = 36 + 8 + 16 = 60
Molecular mass = 2 × vapour density = 2 × 30 = 60
Since molecular mass = empirical formula mass:
Molecular formula = C₃H₈O
(This is propanol or methoxyethane)
Q12(d) — Five primary uses of fats and oils
- Food and energy source — dietary fats provide 9 kcal/g, essential for energy storage
- Manufacture of soap — saponification of fats and oils with NaOH/KOH produces soaps
- Production of glycerol — byproduct of soap manufacture, used in cosmetics and pharmaceuticals
- Manufacture of margarine — hydrogenation of vegetable oils produces solid fat (margarine)
- Lubricants — certain oils are used as industrial lubricants and in cosmetic products (skin moisturisers)
Q12(e) — Polymer from butanedioic acid + hexane-1,6-diamine
Butanedioic acid: HOOC–CH₂CH₂–COOH
Hexane-1,6-diamine: H₂N–(CH₂)₆–NH₂
Condensation reaction: –COOH + H₂N– → –CO–NH– + H₂O
Repeating unit:
–[–CO–CH₂CH₂–CO–NH–(CH₂)₆–NH–]ₙ–
Or written as:
–OC–CH₂CH₂–CO–NH–(CH₂)₆–NH–
Type of polymerisation: Condensation polymerisation (step-growth polymerisation)
Name of linkage: Peptide (amide) linkage — –CO–NH– bond (amide bond)
(This polymer is similar to Nylon-6,6 but made from butanedioic acid instead of hexanedioic acid — it is Nylon-4,6)
Q13(a) — Reagents to convert ethanoyl chloride (CH₃COCl) to:
(i) CH₃COOH (ethanoic acid):
Reagent: Water (H₂O)
CH₃COCl + H₂O → CH₃COOH + HCl
(ii) CH₃COOC₂H₅ (ethyl ethanoate):
Reagent: Ethanol (C₂H₅OH)
CH₃COCl + C₂H₅OH → CH₃COOC₂H₅ + HCl
(iii) CH₃CONH₂ (ethanamide):
Reagent: Ammonia (NH₃)
CH₃COCl + 2NH₃ → CH₃CONH₂ + NH₄Cl
(iv) CH₃COC₆H₅ (phenyl methyl ketone / acetophenone):
Reagent: Benzene in the presence of anhydrous AlCl₃ (Friedel-Crafts acylation)
CH₃COCl + C₆H₆ →(AlCl₃)→ CH₃COC₆H₅ + HCl
(v) CH₃CO–O–OC–CH₃ (ethanoic anhydride):
Reagent: Sodium ethanoate (CH₃COONa)
CH₃COCl + CH₃COONa → (CH₃CO)₂O + NaCl
Q13(b) — Structures of X and Y
Reaction: Propanoic acid + Cl₂/P (sunlight) → X; X + excess NH₃ → Y
Step 1: Propanoic acid undergoes alpha-halogenation (Hell-Volhard-Zelinsky reaction with P/Cl₂):
CH₃CH₂COOH + Cl₂/P → X = 2-chloropropanoic acid (CH₃CHClCOOH)
Step 2: X + excess NH₃ → nucleophilic substitution (Cl replaced by NH₂):
CH₃CHClCOOH + 2NH₃ → Y = 2-aminopropanoic acid (alanine, CH₃CH(NH₂)COOH) + NH₄Cl
X: CH₃–CHCl–COOH Y: CH₃–CH(NH₂)–COOH
2-chloropropanoic acid 2-aminopropanoic acid (alanine)
Q13© — Grignard reaction products X, Y, Z
Grignard reagent (RMgBr) adds to carbonyl compounds; after H⁺ hydrolysis, gives alcohols.
(i) CH₃CHO + CH₃MgBr → H⁺ → X:
Ethanal + methylmagnesium bromide → secondary alcohol
CH₃CHO + CH₃MgBr → CH₃CH(OMgBr)CH₃ → H⁺ → X = CH₃CH(OH)CH₃ (propan-2-ol)
(ii) CH₃COCH₃ + CH₃MgBr → H⁺ → Y:
Propanone + methylmagnesium bromide → tertiary alcohol
(CH₃)₂CO + CH₃MgBr → (CH₃)₃COMgBr → H⁺ → Y = (CH₃)₃COH (2-methylpropan-2-ol)
(iii) CH₃C≡N + CH₃MgBr → H⁺ → Z:
Nitrile + Grignard → imine intermediate → H⁺ hydrolysis → ketone
CH₃CN + CH₃MgBr → [CH₃C(=NMgBr)CH₃] → H₃O⁺ → Z = CH₃COCH₃ (propanone)
Q13(d) — Amino acid R: CH₃CH₂–C(NH₂)(H)–COOH (2-aminobutanoic acid)
(i) Zwitterion of R:
CH₃CH₂–CH(NH₃⁺)–COO⁻
The –NH₂ group gains a proton to become –NH₃⁺, and the –COOH loses a proton to become –COO⁻.
(ii) Major organic product when excess R reacts with bromomethane (CH₃Br):
N-alkylation: The amino group acts as a nucleophile and attacks CH₃Br. With excess CH₃Br, all three N–H bonds can be substituted, and then quaternary ammonium salt forms.
With excess bromomethane:
CH₃CH₂CH(NH₂)COOH + excess CH₃Br →
CH₃CH₂CH(N(CH₃)₃⁺Br⁻)COOH
i.e., the trimethylammonium derivative (quaternary ammonium salt with carboxylic acid group):
Major product: CH₃CH₂CH(N⁺(CH₃)₃)COO⁻ (internal salt/zwitterion with quaternary N)
(iii) Mechanism: Nucleophilic substitution — SN2 mechanism
The lone pair on nitrogen of the –NH₂ group attacks the electrophilic carbon of CH₃Br (bearing the partial positive charge due to C–Br bond polarity), displacing Br⁻ in a single-step backside attack (bimolecular).
Q14(a) — C₆H₁₂ isomers
(i) Reaction of 2-methylpent-2-ene with HBr:
2-Methylpent-2-ene: (CH₃)₂C=CHCH₂CH₃
By Markovnikov’s rule, H⁺ adds to the less substituted carbon (C-3, the =CH– end), and Br⁻ adds to the more substituted carbon (C-2):
Major product: (CH₃)₂CBr–CH₂CH₂CH₃ → 2-bromo-2-methylpentane
Mechanism (electrophilic addition):
Step 1: H⁺ (from HBr) attacks the double bond. H adds to C-3 (less substituted), forming the more s