For every transformation you must know the reagent AND the conditions. Examiners award marks for correct conditions (concentrated vs dilute, aqueous vs ethanolic, heat/reflux).
Key reactions by functional group
Starting group
Reagent & conditions
Product
Reaction type
Alkene
H₂ / Ni catalyst
Alkane
Addition (hydrogenation)
Alkene
HBr (or HCl)
Haloalkane
Electrophilic addition
Alkene
Br₂ (decolourises)
Dibromoalkane
Electrophilic addition (test for C=C)
Alkene
H₂O, H⁺ catalyst (dilute H₂SO₄)
Alcohol
Hydration
Haloalkane
NaOH(aq), warm
Alcohol
Nucleophilic substitution
Haloalkane
KCN in ethanol
Nitrile
Nucleophilic substitution
Haloalkane
excess NH₃
Amine
Nucleophilic substitution
Haloalkane
KOH in ethanol, heat
Alkene
Elimination
1° Alcohol
K₂Cr₂O₇ / H⁺, distil
Aldehyde
Partial oxidation
Aldehyde
K₂Cr₂O₇ / H⁺, reflux
Carboxylic acid
Oxidation
2° Alcohol
K₂Cr₂O₇ / H⁺, reflux
Ketone
Oxidation
3° Alcohol
K₂Cr₂O₇ / H⁺
No reaction
–
Alcohol
conc H₂SO₄, heat (or Al₂O₃)
Alkene
Dehydration (elimination)
Carboxylic acid + alcohol
conc H₂SO₄ catalyst, heat
Ester + water
Esterification (condensation)
Ester
dilute acid, reflux
Acid + alcohol
Hydrolysis
Ester
NaOH(aq), reflux
Carboxylate salt + alcohol
Base hydrolysis (saponification)
Nitrile
H₂ / Ni (or LiAlH₄)
Amine
Reduction
Nitrile
dilute acid, reflux
Carboxylic acid
Hydrolysis
Aldehyde / ketone
NaBH₄ (or H₂/Ni)
Alcohol
Reduction
Carboxylic acid
SOCl₂ (thionyl chloride)
Acyl chloride + steamy fumes of HCl
Substitution
Acyl chloride
H₂O (vigorous, cold)
Carboxylic acid + steamy HCl
Hydrolysis
Acyl chloride
an alcohol
Ester
Substitution
Acyl chloride
an amine (or NH₃)
Amide
Substitution
1° Alcohol / aldehyde
KMnO₄ / H⁺, reflux (purple → colourless)
Carboxylic acid
Oxidation
Amide
dilute acid or NaOH(aq), reflux
Carboxylic acid (or salt) + amine
Hydrolysis
Distinguishing tests — in every paper 2021–2025
Test
Positive result
Identifies
Bromine water
Orange → colourless
C=C double bond (alkene)
Tollens’ reagent
Silver mirror
Aldehyde (not ketone)
Fehling’s / Benedict’s
Blue solution → orange-red precipitate (Cu₂O)
Aldehyde (not ketone)
Acidified K₂Cr₂O₇
Orange → green
1°/2° alcohol, or aldehyde
Acidified KMnO₄
Purple → colourless
1°/2° alcohol, aldehyde, or C=C
SOCl₂ (thionyl chloride)
Steamy fumes (HCl gas)
Carboxylic acid or alcohol (O–H)
NaHCO₃
Fizzes (CO₂)
Carboxylic acid
NaBH₄
Reduced to an alcohol
Aldehyde or ketone (not a carboxylic acid)
✕
The trap: the ORDER you add reagents in
Asked to identify several compounds with a sequence of tests, you are marked on the order, not just the reagents. The 2025 paper is the model case: with ethanoyl chloride, ethanal and ethanol in front of you, water must go first — the acyl chloride reacts vigorously with water, and if you add dichromate or Fehling’s first it reacts with the acyl chloride too and tells you nothing. Then Fehling’s (only the aldehyde responds), then dichromate last (a stronger oxidant, so it finally picks up the alcohol). Weakest, most selective reagent first; strongest last. ℹ
Below here: worth understanding, but not examined recently
Markovnikov’s rule does not appear in any paper from 2021 to 2025, and neither do carbocations. It still explains why addition gives the product it does, so read it once — but do not revise it ahead of structural formulae, optical isomers, chemical tests or polymers. ⚠
Markovnikov’s rule: “the rich get richer”
Mnemonic: the rich get richer. The carbon that’s already rich in hydrogens gets the new H; the halogen goes to the poorer (more substituted) carbon.
When HX adds to an unsymmetrical alkene, H adds to the carbon with more H’s already; X goes to the more substituted carbon. Why? That route goes via the more stable carbocation (tertiary > secondary > primary, because alkyl groups push electron density onto the positive carbon). e.g. propene + HBr → mainly 2-bromopropane. ✓
Anti-Markovnikov: “the poor get poorer”
Mnemonic: the poor get poorer. With peroxides present (radical mechanism), it flips. The hydrogen-poor carbon gets the halogen’s partner instead, so you get the “wrong” product (1-bromopropane from propene). Peroxide → radical → reversal.