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Q: Is there a complete H2 Chemistry organic reactions summary for A Levels? A: Yes. This page maps every functional group interconversion, reagent set, and distinguishing test required by the 9476 syllabus so you can revise organic chemistry as one connected system instead of twelve isolated topics.
Organic chemistry accounts for a significant share of marks across all three H2 Chemistry papers. The challenge is not that any single reaction is difficult - it is that the sheer number of reagent-condition pairs and interconversions can feel overwhelming when studied in isolation.
This summary treats organic chemistry as a reaction map. Each functional group is a node; each reaction is a directed edge labelled with reagents, conditions, and the mechanism type the examiner expects you to name. If you can trace routes across the map, you can handle synthesis questions, Paper 1 deductions, and Paper 3 planning problems with confidence.
Read with your Data Booklet open. The Data Booklet lists IR absorption ranges, 1H NMR chemical shifts, and qualitative analysis observations. This summary supplies the reaction logic; the Data Booklet supplies the reference data.
Trace pathways, not isolated reactions. When you see "alcohol", immediately ask: what can I make from it, and what can I make it from?
Drill reagents and conditions separately. The cheat sheet in Section 6 isolates the exact phrasing examiners expect.
For the equations and constants you must memorise (as opposed to look up), see the H2 Chemistry Formula Sheet.
Functional group reference table
The table below lists every functional group you need for the 9476 syllabus, with the general formula, a simple example, and the key reaction types associated with each group.
Weak acidity, electrophilic substitution, esterification with acyl chloride
Reaction map by functional group interconversion
This is the core of organic chemistry revision. Each subsection below covers one functional group as a starting material and lists the reactions that convert it into other functional groups.
4.1 Alkene reactions (electrophilic addition)
Alkenes are electron-rich at the C=C double bond and undergo electrophilic addition.
Reagent and conditions
Product
Mechanism
Notes
HBr (gas or concentrated solution)
Halogenoalkane
Electrophilic addition
Markovnikov's rule applies to unsymmetrical alkenes
H2O / concentrated H2SO4 (catalyst)
Alcohol
Electrophilic addition
Two-step: addition of H2SO4, then hydrolysis
Br2 (in organic solvent or aqueous)
1,2-dibromoalkane
Electrophilic addition
Decolourisation of bromine is the classic alkene test
H2 / Ni catalyst, heat
Alkane
Catalytic hydrogenation
Also Pt or Pd as catalyst
Cold, dilute KMnO4
Diol (1,2-diol)
Oxidation
Purple → decolourised (or brown MnO2); test for unsaturation
Hot, concentrated, acidified KMnO4
Cleavage products (ketones, carboxylic acids)
Oxidative cleavage
Product depends on substitution around the double bond
4.2 Halogenoalkane reactions
Halogenoalkanes are versatile intermediates because the C-X bond is polar and the carbon is electrophilic.
Nucleophilic substitution (\(\text{S}\text{N}1\) or \(\text{S}\text{N}2\))
Nucleophile and conditions
Product
Notes
NaOH(aq), heat under reflux
Alcohol
Hydroxide ion as nucleophile
KCN in ethanol-water, heat under reflux
Nitrile (one extra carbon)
Cyanide ion as nucleophile; extends the carbon chain
Excess concentrated NH3 in ethanol, sealed tube, heat
Amine
Ammonia as nucleophile; excess limits further substitution
Elimination
Reagent and conditions
Product
Notes
NaOH in ethanol, heat under reflux
Alkene
Ethanolic (not aqueous) NaOH favours elimination over substitution
The competition between substitution and elimination depends on the base/nucleophile, the solvent, and the degree of substitution of the halogenoalkane.
4.3 Alcohol reactions
Alcohols sit at the centre of the organic reaction map. They connect to alkenes, halogenoalkanes, carbonyl compounds, and esters.
Reaction
Reagent and conditions
Product
Notes
Oxidation (1\textdegree alcohol)
K2Cr2O7 / dilute H2SO4, distil
Aldehyde
Distil immediately to prevent further oxidation
Oxidation (1\textdegree alcohol)
K2Cr2O7 / dilute H2SO4
Oxidation (2\textdegree alcohol)
K2Cr2O7 / dilute H2SO4
Oxidation (3\textdegree alcohol)
-
No reaction
Resistant to oxidation by K2Cr2O7
Dehydration
Excess concentrated H2SO4, 170 \textdegree C
Alkene
Elimination of water
Esterification
Carboxylic acid + concentrated H2SO4 catalyst, heat under reflux
Ester
Reversible; equilibrium shifted by excess reagent or removal of product
Halogenation
PCl3, PCl5, or SOCl2
4.4 Aldehyde and ketone reactions
Both aldehydes and ketones contain the carbonyl group (C=O). The key difference is that aldehydes can be oxidised further, while ketones cannot.
Reaction
Reagent and conditions
Product
Notes
Reduction
NaBH4 in methanol (or aqueous)
Alcohol (1\textdegree from aldehyde, 2\textdegree from ketone)
Nucleophilic addition of hydride
Nucleophilic addition of HCN
HCN / trace NaCN (or KCN + dilute acid)
Hydroxynitrile (cyanohydrin)
CN− is the nucleophile; extends the carbon chain
Tollens' test
Ag(NH3)2+ (Tollens' reagent), warm
Silver mirror (from aldehyde only)
Ketones give no reaction
Fehling's test
Fehling's solution (Cu2+ complex), heat
Red-brown precipitate of Cu2O (from aldehyde only)
Ketones give no reaction
Iodoform test
I2 / NaOH(aq), warm
Yellow precipitate of CHI3
Positive for CH3CO-
4.5 Carboxylic acid reactions
Reaction
Reagent and conditions
Product
Notes
Esterification
Alcohol + concentrated H2SO4 catalyst, heat under reflux
Ester
Same reaction as in Section 4.3 but viewed from the acid side
Reduction
LiAlH4 in dry ether
Primary alcohol
NaBH4 is too mild to reduce carboxylic acids
Acyl chloride formation
SOCl2 (thionyl chloride)
Acyl chloride
Gaseous by-products (SO2, HCl) make purification easier
Acyl chlorides are more reactive than carboxylic acids and undergo rapid nucleophilic substitution with water, alcohols, amines, and ammonia.
4.6 Amine reactions
Reaction
Reagent and conditions
Product
Notes
Basicity
Acts as a Bronsted-Lowry base
Accepts a proton from acids
Aliphatic amines are stronger bases than ammonia; aromatic amines (e.g. phenylamine) are weaker
Acylation
Acyl chloride at room temperature
Substituted amide
Nucleophilic substitution; removes HCl
Reaction with HNO2 (aliphatic 1\textdegree)
NaNO2 + dilute HCl, low temperature
Alcohol + N2 gas
Not synthetically useful; effervescence observed
Reaction with HNO2 (aromatic 1\textdegree)
NaNO2 + dilute HCl, below 10 \textdegree C
Diazonium salt
Coupling with phenol gives azo dye
4.7 Arene reactions (electrophilic substitution)
The delocalised π system of benzene is electron-rich and attacks electrophiles, but addition would destroy aromaticity, so substitution is favoured.
Reaction
Reagent and conditions
Product
Electrophile
Nitration
Concentrated HNO3 + concentrated H2SO4, 50-55 \textdegree C
Nitrobenzene
NO2+ (nitronium ion)
Halogenation
Br2 (liquid) + anhydrous FeBr3 (or AlBr3
Friedel-Crafts alkylation
R-Cl + anhydrous AlCl3 catalyst
Alkylbenzene
R+ (carbocation)
Friedel-Crafts acylation
R-COCl + anhydrous AlCl3 catalyst
Acylbenzene (aryl ketone)
R-CO+ (acylium ion)
Phenol and phenylamine rings are activated (electron-donating substituents) and react more readily, often without a catalyst and preferentially at the 2- and 4-positions.
Distinguishing tests summary
A common Paper 2 or Paper 3 question asks you to identify an unknown compound or distinguish between two given compounds. The table below pairs each test reagent with what it distinguishes.
Reagent / Test
Positive result
Distinguishes between
Br2 (aq) decolourisation
Rapid decolourisation
Alkene vs alkane
KMnO4 (aq, cold, dilute) decolourisation
Purple → colourless/brown
Alkene vs alkane
Na2CO3 (aq) effervescence
CO2 gas evolved
Carboxylic acid vs alcohol/phenol
Tollens' reagent (warm)
Silver mirror
Aldehyde vs ketone
Fehling's solution (heat)
Red-brown precipitate
Aldehyde vs ketone
I2 / NaOH (warm)
Yellow precipitate of CHI3
Methyl carbonyl (CH3CO-
PCl5 (room temperature)
Steamy fumes of HCl
-OH group (alcohol, carboxylic acid) vs others
FeCl3 (aq)
Purple/violet coloration
Phenol vs aliphatic alcohol
2,4-DNPH
Orange/yellow precipitate
Carbonyl (aldehyde or ketone) vs alcohol
Litmus / pH indicator
Acidic response
Carboxylic acid vs ester
Reagents and conditions cheat sheet
Examiners award marks for precise reagent names and conditions. Vague answers such as "heat" or "acid" will not earn full credit. Memorise the exact phrasing below.
Shorthand you might write
What the examiner wants to see
"Heat"
Heat under reflux (for reactions in solution)
"NaOH"
State aqueous or ethanolic and specify heat under reflux
"Acid catalyst"
Concentrated H2SO4 as catalyst
"Oxidising agent"
K2Cr2O7 / dilute H2SO4 (state heat under reflux or distil)
"Reducing agent for C=O"
NaBH4 in methanol (or aqueous)
"Strong reducing agent for COOH"
LiAlH4 in dry ether
"Halogen carrier"
Anhydrous FeBr3 or AlCl3
"Nitrating mixture"
Concentrated HNO3 + concentrated H2SO4, 50-55 \textdegree C
"Form acyl chloride"
SOCl2 (thionyl chloride)
"Tollens' reagent"
Ag(NH3)2+(aq), warm in a water bath
"Fehling's solution"
Fehling's solution, heat
Always state the physical conditions (temperature, reflux vs distil, solvent) alongside the reagent.
Common synthesis pathways
Synthesis questions in Paper 3 (and occasionally Paper 2) ask you to convert one compound into another in multiple steps. Practise tracing these pathways across the reaction map above.
Expect 1-2 structured questions on organic chemistry, often worth 8-15 marks each.
Common question types: draw mechanisms (electrophilic addition, nucleophilic substitution, electrophilic substitution), state reagents and conditions, explain observations in distinguishing tests, and predict products of multi-step syntheses.
Synthesis planning questions (2-5 steps) are a hallmark of Paper 3.
You may be asked to design a route from a given starting material to a target product, justifying each step with reagents, conditions, and the type of reaction.
Spectroscopy interpretation (IR, mass spec, 1H NMR) may accompany organic identification questions. Use the Data Booklet reference ranges.
FAQ
How many organic reactions do I need to know for H2 Chemistry?
The 9476 syllabus covers roughly 40-50 distinct reagent-condition-product combinations across 12 functional groups. That sounds like a lot, but many reactions share the same mechanism type (e.g. multiple electrophilic additions to alkenes), so organising by mechanism reduces the memory load significantly.
What is the best way to memorise organic reactions?
Build the reaction map yourself on a blank sheet of paper: start with ethene or ethanol at the centre and draw every interconversion you can recall, labelling the arrows with reagents and conditions. Check your map against this summary and fill in gaps. Repeat until you can reconstruct the map from memory in under ten minutes.
Do I need to draw mechanisms for every reaction?
No. The 9476 syllabus requires mechanisms for specific reaction types: electrophilic addition (alkenes), nucleophilic substitution (\(\text{S}\text{N}1\) and \(\text{S}\text{N}2\) for halogenoalkanes), nucleophilic addition (HCN to carbonyl), and electrophilic substitution (arenes). For other reactions, you need reagents, conditions, and products but not the full curly-arrow mechanism.
How do I distinguish between an aldehyde and a ketone in an exam?
Use Tollens' reagent (silver mirror with aldehydes, no reaction with ketones) or Fehling's solution (red-brown precipitate with aldehydes, no reaction with ketones). State the observation clearly and name the reagent precisely.
What is the most common mistake in synthesis questions?
Forgetting to specify conditions. Writing "add NaOH" without stating aqueous or ethanolic, or without stating "heat under reflux", will lose you marks. Always include the solvent, temperature, and technique (reflux, distil, sealed tube).
