Grade 12 Organic Chemistry – Comprehensive Study Notes
BASIC UNDERSTANDING
Organic Chemistry – branch of chemistry that studies carbon‐containing compounds.
Organic molecules – any molecule that contains at least one C atom.
Elements commonly present in Grade 12 organic compounds:
Carbon (C), Hydrogen (H), Oxygen (O)
Halogens: Bromine (–Br), Chlorine (–Cl), Iodine (–I) → shown collectively as –X
CARBON CLASSIFICATION
Primary C (1°) – attached to ONE other carbon.
Secondary C (2°) – attached to TWO other carbons.
Tertiary C (3°) – attached to THREE other carbons.
Rule applies analogously to alcohols when –OH is bonded to these carbons (primary, secondary, tertiary alcohols).
BASIC TERMINOLOGIES
Hydrocarbons – compounds containing only C and H.
Saturated hydrocarbons – only single C–C bonds.
Unsaturated hydrocarbons – at least one C=C or C≡C bond.
Homologous series – family with same functional group & general formula; successive members differ by a \text{–CH}_2 unit.
Functional group – atom/group/bond that determines chemical & physical properties.
Molecular formula – actual number of each atom in a molecule.
Condensed structural formula – shows bonding sequence without all bond lines.
Structural formula – displays every atom and all bonds.
Isomers – same molecular formula, different structural formulae.
ORGANIC MOLECULAR STRUCTURES & HOMOLOGOUS SERIES
Table summary (≤ 8 carbons):
Alkanes \text{C}n\text{H}{2n+2} suffix –ane FG: None
Alkenes \text{C}n\text{H}{2n} suffix –ene FG: C=C
Alkynes \text{C}n\text{H}{2n-2} suffix –yne FG: C≡C
Haloalkanes \text{C}n\text{H}{2n+1}X prefix: halo- FG: C–X
Alcohols \text{C}n\text{H}{2n+1}OH suffix –ol FG: –OH
Aldehydes \text{C}n\text{H}{2n}O suffix –al FG: –CHO
Ketones \text{C}n\text{H}{2n}O suffix –one FG: –CO– (carbonyl in chain)
Carboxylic acids \text{C}n\text{H}{2n}O_2 suffix –oic acid FG: –COOH
Esters \text{C}n\text{H}{2n}O_2 suffix –oate FG: –COO–
IUPAC NAMING RULES (≤ 8 C, ≤ 1 FG type, ≤ 3 substituents)
Identify functional group → choose suffix.
Select longest chain containing FG (max 8 C).
Number chain:
Begin nearest FG (or nearest substituent for alkanes/haloalkanes).
For multiple bonds use smaller locator of bonded C’s.
Root names: \text{1 C meth–, 2 C eth–, 3 C prop–, 4 C but–, 5 C pent–, 6 C hex–, 7 C hept–, 8 C oct–, 9 C non–, 10 C dec–}
Indicate FG position (except carboxylic acid & aldehyde – C1 implicit).
Deal with substituents:
Prefix –yl for alkyl groups (methyl, ethyl).
Alphabetical order; use multiplicative prefixes di-, tri-, tetra-, etc.
Separate numbers with commas, numbers & letters with hyphens.
Examples:
2,4,4-trimethylhexane (alkane)
3,5,5-trimethyl-2-hexene (alkene)
3-methyl-1-butyne (alkyne)
3-ethyl-6-methylheptanoic acid (carboxylic acid)
Ethyl butanoate (ester)
3,5-dimethylheptan-2-one (ketone)
3-bromo-3-chloro-2-methylpentane (haloalkane)
2,3,6-trimethyloctan-4-ol (alcohol)
STRUCTURE & PHYSICAL PROPERTIES
Investigated properties: Boiling point, Melting point, Vapour pressure.
Definitions:
Boiling point (bp) – T at which P{\text{vapour}} = P{\text{atm}}.
Melting point (mp) – T where solid ⇌ liquid.
Volatility – ease of vaporisation (high volatility → high vapour pressure, low bp).
Intermolecular forces (IMF) in increasing strength:
London/dispersion (induced dipole)
Dipole–dipole
Hydrogen bonding (H with N, O, F)
General trend:
Stronger IMF → ↑ bp/mp, ↓ vapour pressure.
Relationships
Functional group (polarity & H-bonding ability):
Weak IMF (alkanes < alkenes < alkynes) < haloalkanes < esters < ketones ≈ aldehydes < alcohols < carboxylic acids (strongest; dimerise).Chain length: longer chain → larger surface area → stronger London forces → ↑ bp/mp, ↓ vapour pressure.
Branching: branched chains hinder close packing → weaker London forces → ↓ bp/mp, ↑ vapour pressure compared with straight isomer.
Example MCQ (ordered by increasing bp): pentane < pentan-1-ol < pentanoic acid.
TYPES OF REACTIONS
1 Oxidation / Combustion
Reaction with O2; products always CO2 + H_2O + energy.
Generic: \text{alkane} + O2 \rightarrow CO2 + H_2O
Balancing tips: (i) place 2 before hydrocarbon, (ii) balance C, (iii) balance H, (iv) balance O.
2 Substitution (Saturated: alkanes, haloalkanes)
Functional group or H replaced by another FG; need heat/UV.
Halogenation: \text{alkane} + X_2 \rightarrow \text{haloalkane} + HX
Hydrolysis: \text{haloalkane} + H_2O \rightarrow \text{alcohol} + HX (or NaOH).
3 Addition (Unsaturated: alkenes, alkynes)
Break π-bond, form saturated product.
Follows Markovnikov’s rule (H adds to C already bearing more H) → major product.
Types:
Hydrogenation: \text{alkene} + H_2 \xrightarrow{\text{Pt/Ni}} \text{alkane}
Halogenation: \text{alkene} + X_2 \rightarrow \text{haloalkane}
Hydrohalogenation: \text{alkene} + HX \rightarrow \text{haloalkane}
Hydration: \text{alkene} + H2O \xrightarrow{\text{conc. H2SO_4}} \text{alcohol}
4 Elimination (Saturated to unsaturated)
Remove atoms/groups from adjacent C’s; often reverse of addition.
Zaitsev’s rule – most substituted alkene favoured.
Dehydrohalogenation: \text{haloalkane} \xrightarrow{\text{base}} \text{alkene} + HX
Dehydration of alcohols: \text{alcohol} \xrightarrow{\text{conc. H2SO4}} \text{alkene} + H_2O
Dehydrogenation: \text{alkane} \xrightarrow{\text{Pt/Ni}} \text{alkene} + H_2
Cracking: large alkane → shorter alkane + alkene.
5 Esterification
Alcohol + carboxylic acid \xrightarrow{\text{conc. H2SO4, \Delta}} ester + H_2O.
Ester named alkyl alkanoate (alkyl from alcohol, alkanoate from acid).
Example: butanol + propanoic acid → butyl propanoate + H_2O.
PLASTICS & POLYMERS
Macromolecule – very large molecule (many atoms).
Monomer – small molecule that can link repetitively.
Polymer – large molecule of covalently bonded repeating monomer units.
Polymerisation – reaction forming a polymer.
Addition polymerisation
Monomers must contain C=C/C≡C (same monomer usually).
No side product; polymer name = poly(monomer). Example: n(CH2=CH2) \rightarrow (CH2–CH2)_n (polyethene).
Condensation polymerisation
Two different monomers with functional groups (–COOH, –OH, –NH_2 …).
Small molecule (often H_2O) eliminated each linkage.
Example: formation of polyesters via esterification between diacid & diol.
Distinguishing features
Addition: double bond → single product.
Condensation: FG’s react → polymer + small molecule.
Industrial uses of polyethene (polythene)
Sandwich & freezer bags
Cling wrap
Liners for ponds/tanks
Car covers & moisture barriers in construction
Squeeze bottles & water pipes
Wire/cable insulation, extrusion coating, etc.
EXAM-STYLE ACTIVITIES (selected answers)
\text{C}2H4O_2 isomers: ethanoic acid (strong H-bond, low vapour pressure, higher bp) vs methyl methanoate (ester).
Complete combustion of octane: C8H{18} + \tfrac{25}{2}O2 \rightarrow 8CO2 + 9H_2O (or doubled).
Reaction identification: hydration vs hydrogenation, substitution vs hydrolysis, etc.
ETHICAL & PRACTICAL NOTES
Combustion releases energy but also CO_2 → greenhouse implications.
Plastic pollution arises from persistence of addition polymers like polyethene; motivates bio-degradable condensation polymers.
Industrial cracking provides economically valuable smaller olefins for polymer production.
QUICK REFERENCE EQUATIONS (all balanced)
Combustion: CH4 + 2O2 \rightarrow CO2 + 2H2O
Halogenation: C2H6 + Br2 \xrightarrow{hv} C2H_5Br + HBr
Hydrolysis: C2H5Br + H2O \rightarrow C2H_5OH + HBr
Hydrogenation: CH2=CH2 + H2 \xrightarrow{Ni} CH3CH_3
Dehydration: C2H5OH \xrightarrow{H2SO4,\Delta} CH2=CH2 + H_2O
Esterification: C3H7OH + CH3COOH \xrightarrow{H2SO4,\Delta} C3H7OOCCH3 + H_2O
These bullet-point notes cover every term, rule, trend, reaction, polymer concept, example and numerical reference presented in the transcript, providing a full study replacement for the original slides.