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Organic Chemistry XII · 5 Chapters · 33 marks

Organic Chemistry Formula Reference

Haloalkanes to Biomolecules — key reactions, rate laws, tests and relationships.

⚡ Critical Reactions — Memorise These First

SN2 Raterate = k[RX][Nu⁻]
SN1 Raterate = k[RX]
Carbocation3° > 2° > 1° > CH₃⁺
Basicity (water)2°aliphatic > 1° > NH₃ > aniline
AcidityRCOOH > PhOH > H₂O > ROH
NA ReactivityHCHO > RCHO > RCOR'
DiazotisationArNH₂ + NaNO₂ + HCl (0–5°C)
Tollens'RCHO + 2[Ag(NH₃)₂]⁺ → Ag↓
06 Haloalkanes & Haloarenes 6 marks
Reactivity Order (Nucleophilic Substitution)
RI > RBr > RCl > RF
C–I bond weakest → easiest to break. RF strongest bond → least reactive.
SN2 Rate Law
rate = k [RX][Nu⁻]
Bimolecular, one step, backside attack → Walden inversion. Favoured: 1° RX, strong nucleophile, polar aprotic solvent.
SN1 Rate Law
rate = k [RX]
Unimolecular, 2-step via carbocation → racemisation. Favoured: 3° RX, weak nucleophile, polar protic solvent.
Carbocation Stability
3° > 2° > 1° > CH₃⁺
Determines SN1 reactivity. Stability due to hyperconjugation and inductive effect of alkyl groups.
Optical Rotation
[α] = α / (l × c)
[α] = specific rotation; α = observed rotation; l = path length (dm); c = concentration (g/mL).
07 Alcohols, Phenols & Ethers 6 marks
Acidity Order
RCOOH > PhOH > H₂O > ROH > RH
Phenol more acidic than alcohol: phenoxide ion stabilised by resonance with benzene ring.
Lucas Test
ZnCl₂ + conc. HCl (Lucas reagent) 3° → immediate turbidity 2° → turbidity in ~5 min 1° → no turbidity (at RT)
Tests 1°/2°/3° alcohols. Turbidity = formation of insoluble alkyl chloride.
Victor Meyer Test
1° → red (nitroso compound) 2° → blue 3° → colourless
Tests 1°/2°/3° alcohols. Converts to nitroalkane then reacts with HNO₂.
Esterification (Fischer)
RCOOH + R'OH ⇌ RCOOR' + H₂O
Catalyst: conc. H₂SO₄. Reversible — use excess reactant or remove water to shift forward.
08 Aldehydes, Ketones & Carboxylic Acids 8 marks
Nucleophilic Addition Reactivity
HCHO > RCHO > RCOR'
Decreasing due to +I effect of alkyl groups (reduces electrophilicity) and steric hindrance.
Tollens' Test (Silver Mirror)
RCHO + 2[Ag(NH₃)₂]⁺ + H₂O → RCOOH + 2Ag↓ + 4NH₃
Only aldehydes (not ketones). Formic acid (HCOOH) also gives silver mirror.
Fehling's Test
RCHO + 2Cu²⁺ + 4OH⁻ → RCOO⁻ + Cu₂O↓ + 2H₂O
Brick-red precipitate Cu₂O. Only aliphatic aldehydes (not aromatic, not ketones).
Aldol Condensation
2CH₃CHO → CH₃CH(OH)CH₂CHO → CH₃CH=CHCHO
Catalyst: dilute NaOH. Requires α-H. β-hydroxy aldehyde dehydrates to α,β-unsaturated carbonyl.
Cannizzaro Reaction
2HCHO + NaOH(conc.) → CH₃OH + HCOONa
Disproportionation. Only for aldehydes WITHOUT α-H (e.g., HCHO, PhCHO).
Carboxylic Acid Acidity
pKa: HCOOH (3.74) < CH₃COOH (4.74) EWG on α-C → lower pKa (stronger acid)
CCl₃COOH > CHCl₂COOH > CH₂ClCOOH > CH₃COOH. Carboxylic acids react with NaHCO₃; phenols do NOT.
09 Amines 6 marks
Basicity Order (in water)
2° aliphatic > 1° aliphatic > NH₃ > aniline (C₂H₅)₂NH > C₂H₅NH₂ > (C₂H₅)₃N > NH₃
In gas phase: 3° > 2° > 1°. In water: solvation makes 2° most basic. Aniline much weaker due to resonance.
pKb Values (approx.)
Aniline: pKb ≈ 9.4 Aliphatic amines: pKb ≈ 3–4
Lower pKb = stronger base. EWG on ring → weaker base (higher pKb); EDG → stronger base.
Hinsberg's Test
1°: soluble ppt in NaOH 2°: insoluble ppt 3°: no reaction
Reagent: C₆H₅SO₂Cl (benzenesulfonyl chloride). 1° gives sulfonamide with acidic N–H (soluble in NaOH).
Diazotisation
ArNH₂ + NaNO₂ + HCl (0–5°C) → ArN₂⁺Cl⁻
Temperature CRITICAL: 0–5°C prevents decomposition of diazonium salt. Only for primary aromatic amines.
Carbylamine Test
R-NH₂ + CHCl₃ + KOH → R-NC (isocyanide)
Isocyanide has offensive smell. Confirmatory test for PRIMARY amines only.
10 Biomolecules 7 marks
Glucose Formula & Structure
C₆H₁₂O₆ (open chain: aldohexose) Cyclic: α-D-glucose (OH at C1 axial) / β-D-glucose (equatorial)
Haworth projection: pyranose (6-membered ring). Mutarotation: interconversion of α and β forms.
Reducing vs Non-Reducing Sugars
Reducing: free −CHO or potential −CHO Non-reducing: sucrose (no free anomeric C)
Reducing sugars reduce Tollens/Fehling/Benedict. Maltose, lactose = reducing; sucrose = non-reducing.
Sucrose Linkage
α-D-glucose + β-D-fructose (1→2 glycosidic bond)
Both anomeric carbons involved → no free anomeric C → non-reducing. Hydrolysis → equimolar glucose + fructose.
DNA vs RNA
DNA: deoxyribose, ATGC, double helix, A–T (2H), G–C (3H) RNA: ribose, AUGC, single strand
DNA stores genetic info; RNA involved in protein synthesis. Antiparallel strands in DNA.
Peptide Bond
—CO—NH— (amide bond)
Formed by condensation between −COOH and −NH₂, releasing H₂O. Hydrolysis breaks peptide bond.
Protein Structure Levels
1° → 2° (α-helix/β-sheet) → 3° (folding) → 4° (subunits)
Denaturation: loss of 2°/3°/4° structure (not 1°). Enzymes lose activity on denaturation.