AQA A-Level Chemistry: Organic Chemistry Advanced — Complete Revision Guide (7405)

Organic chemistry advanced is the A2 organic course on AQA 7405. It picks up where the AS foundations left off and adds the carbonyl group in all its forms (aldehydes, ketones, carboxylic acids, esters, acyl chlorides, amides, amino acids), aromatic chemistry (benzene and electrophilic substitution), amines, biological molecules (proteins, DNA), condensation polymers, and multi-step synthesis including asymmetric methods. Paper 2 examiners reward two skills above all: stereochemistry awareness — the routine identification of chiral centres and the consequences of racemic mixtures — and mechanism fluency, the ability to draw curly-arrow mechanisms quickly and correctly.

This topic is heavily synoptic. The mechanisms here build directly on the organic foundations curly-arrow vocabulary. Carbonyl and aromatic identification depends on the IR and NMR techniques covered in analytical chemistry. Benzene's delocalisation is the MO picture from bonding, and the acidity of carboxylic acids and amino acids uses the Ka framework from physical chemistry. Time spent here returns across the whole A2 paper.

This guide walks through the ten sub-topics in the AQA 7405 organic advanced syllabus, with the marks they typically carry, the common pitfalls, and a worked example per section. For each topic you will find a link to the matching LearningBro lesson in the Organic Chemistry Advanced course.

What the AQA 7405 Specification Covers

AQA A-Level Chemistry (7405) is examined through three papers: Paper 1 (Inorganic and Physical, 2h, 105 marks), Paper 2 (Organic and Physical, 2h, 105 marks) and Paper 3 (Practical and Synoptic, 2h, 90 marks). Organic advanced corresponds to specification sections §3.3.8 (optical isomerism), §3.3.9 (aldehydes and ketones), §3.3.10 (carboxylic acids and derivatives), §3.3.11 (aromatic chemistry), §3.3.12 (amines), §3.3.13 (polymers), and §3.3.14 (amino acids, proteins, DNA). It is examined principally on Paper 2 with a substantial Paper 3 footprint through identification and synthesis questions.

Sub-topic	Spec area	Typical paper weight
Aldehydes and ketones: tests and reactions	§3.3.9	4-6 marks
Carbonyls and carboxylic acids	§3.3.9-§3.3.10	3-5 marks
Carboxylic acid derivatives	§3.3.10	4-6 marks
Aromatic chemistry and electrophilic substitution	§3.3.11	5-8 marks
Friedel-Crafts and aromatic mechanisms	§3.3.11	4-6 marks
Amines: structure, basicity and synthesis	§3.3.12	4-6 marks
Amino acids, proteins and DNA	§3.3.14	4-6 marks
Condensation polymers	§3.3.13	3-5 marks
Organic synthesis pathways	§3.3.10-§3.3.14	6-10 marks
Multi-step and asymmetric synthesis	§3.3.8 + synoptic	4-8 marks

These weights are estimates, modelled on recent AQA 7405 papers. What is reliable is that an extended-response synthesis question — typically eight to ten marks — appears on essentially every Paper 2, and an aromatic-mechanism question is now almost a fixture.

Aldehydes and Ketones: Tests and Reactions

The carbonyl group C=O is polar. Aldehydes (RCHO) have the carbonyl at the end of a chain; ketones (RCOR') have it within. Both react by nucleophilic addition at the electrophilic carbon. Aldehydes are oxidised easily to carboxylic acids; ketones resist oxidation — the single difference underpinning every distinguishing test.

The three standard tests are Tollens, Fehling, and acidified potassium dichromate. Tollens is ammoniacal silver nitrate; aldehydes reduce Ag+ to a silver mirror, ketones give no change. Fehling is alkaline Cu2+ complexed with tartrate; aldehydes reduce Cu2+ to a brick-red Cu2O precipitate, ketones do not react. Acidified K2Cr2O7 turns orange to green with aldehydes but not ketones.

For nucleophilic addition itself, the examinable reactions are reduction by NaBH4 (giving a primary alcohol from an aldehyde, a secondary alcohol from a ketone) and addition of HCN/KCN to give a hydroxynitrile. The HCN addition introduces a new chiral centre and gives a racemic mixture because attack on the planar carbonyl is equally likely from either face.

A common pitfall is to write Tollens as simply AgNO3 — the ammonia is essential, since [Ag(NH3)2]+ is the active species. Another is to forget that HCN addition creates a chiral centre only when the two R groups on the carbonyl are different. See the aldehydes and ketones lesson.

Carbonyl Compounds and Carboxylic Acids

This section ties carbonyl chemistry into the wider oxidation-state sequence: primary alcohol → aldehyde → carboxylic acid; secondary alcohol → ketone (full stop). The interconversions are central to synthesis routes and to identification problems on Paper 3.

Carboxylic acids (RCOOH) are weak acids (typical pKa around 4-5), more acidic than alcohols because the conjugate base RCOO- is stabilised by delocalisation of the negative charge across both oxygens. They react with sodium carbonate to give CO2 effervescence — the standard distinguishing test against alcohols and phenols (phenols are too weak to evolve CO2 from NaHCO3 at room temperature). They react with bases to give salts, and with alcohols under acid catalysis to give esters via esterification, an equilibrium reaction with water as the by-product.

Worked example. Identify a compound with molecular formula C3H6O2 that fizzes with sodium carbonate and gives a 1H NMR peak around 11 ppm. The carbonate test indicates a carboxylic acid; C3H6O2 with -COOH is propanoic acid CH3CH2COOH. The 11 ppm signal is the carboxylic O-H.

A common pitfall is to confuse the acidity ordering: carboxylic acid (most acidic) > phenol > alcohol > water (in the alcohol-water comparison, water is actually slightly more acidic, but the examinable trend is carboxylic > phenol > water > alcohol). See the carbonyls and carboxylic acids lesson.

Carboxylic Acid Derivatives: Esters and Amides

The carboxylic acid derivatives are esters (RCOOR'), acyl chlorides (RCOCl), acid anhydrides ((RCO)2O) and amides (RCONH2). All come from formal substitution of -OH on the carboxylic acid by another leaving group. Reactivity towards nucleophiles runs acyl chloride > anhydride > ester > amide, reflecting leaving-group ability and resonance donation back into the carbonyl.

Esters are made by esterification (carboxylic acid + alcohol with H2SO4, reversible) or by acyl chloride or anhydride with an alcohol (irreversible, much faster). They are hydrolysed by acid (slow, reversible) or alkali (fast, irreversible — saponification when applied to fats). Esters are widely used as solvents, perfumes and plasticisers.

Amides are made by acyl chloride or anhydride with ammonia or an amine, and hydrolysed under harsh acid or base back to the carboxylic acid and amine. The amide C-N bond has partial double-bond character from resonance, making amides unusually unreactive and planar — the same effect constrains the peptide bond in proteins.

A common pitfall is to draw the ester reverse — RCO-OR' is correct. Another is to write ammonia displacing chloride from an acyl chloride without showing two equivalents of NH3 are needed (one to react, one to neutralise HCl). See the derivatives lesson.

Aromatic Chemistry: Benzene and Electrophilic Substitution

Benzene C6H6 has six equivalent C-C bonds of length 0.139 nm, intermediate between a single (0.154 nm) and double (0.134 nm) bond. The classical Kekulé structure with alternating single and double bonds fails to explain this equality, the lack of typical alkene reactivity, and the enthalpy of hydrogenation — around 150 kJ mol^-1 less exothermic than predicted for three localised double bonds. This delocalisation energy is the thermodynamic signature of aromaticity. The modern picture is a planar ring of six sp2 carbons with six p orbitals overlapping to give a delocalised π system that satisfies Hückel's 4n+2 rule with n = 1.

Because of this stability, benzene undergoes electrophilic substitution rather than addition: an electrophile attacks the ring to form a positively charged arenium intermediate, and a proton is lost to restore aromaticity. Three examinable substitutions are nitration (HNO3/H2SO4 generating NO2+), halogenation (Br2 with FeBr3 catalyst), and Friedel-Crafts acylation and alkylation.

A common pitfall is to write addition products with benzene under standard conditions — benzene preserves its aromaticity at all costs. Another is to draw the arenium intermediate as if the ring were still fully aromatic. See the aromatic chemistry lesson.

Friedel-Crafts and Aromatic Mechanisms

The Friedel-Crafts reactions, developed by Friedel and Crafts in 1877, attach alkyl or acyl groups to benzene via Lewis-acid-catalysed electrophilic substitution. In acylation, an acyl chloride RCOCl plus AlCl3 generates an acylium ion RCO+, which attacks the ring to give an aryl ketone. In alkylation, RCl plus AlCl3 generates a carbocation R+ — less useful synthetically because the alkyl product is more reactive than the starting material, giving polysubstitution and rearrangement.

Acylation is the workhorse: the carbonyl deactivates the ring against further substitution, so the reaction stops cleanly at the monosubstituted product. The aryl ketone can then be reduced to the alkylbenzene — a longer but cleaner route than direct alkylation.

Worked example. Show the mechanism for nitration of benzene. (1) HNO3 + H2SO4 → NO2+ + HSO4- + H2O. (2) NO2+ attacks the π system, forming the arenium intermediate. (3) HSO4- removes the H, restoring aromaticity and regenerating H2SO4. Three curly arrows in total; lose marks if any is missing or points the wrong way.

A common pitfall is to forget the Lewis-acid catalyst — without AlCl3 (or FeBr3 for halogenation, or H2SO4 for nitration), the electrophile is not generated. See the Friedel-Crafts lesson.

Amines: Structure, Basicity and Synthesis

Amines are derivatives of ammonia in which one, two or three hydrogens have been replaced by alkyl or aryl groups, giving primary (RNH2), secondary (R2NH) and tertiary (R3N) amines. The nitrogen lone pair accepts a proton, making amines bases. Aliphatic amines are stronger bases than ammonia because alkyl groups push electron density onto the nitrogen, stabilising the protonated form. Aromatic amines such as phenylamine are weaker bases than ammonia because the nitrogen lone pair is partially delocalised into the ring, reducing its availability for protonation.

Two synthesis routes feature heavily on Paper 2. Aliphatic amines are made by nucleophilic substitution of a halogenoalkane with ammonia (giving a mixture of primary, secondary, tertiary amines and quaternary ammonium salts because each new amine is itself a nucleophile) or, more cleanly, by reduction of a nitrile RCN with LiAlH4 or H2/Ni to RCH2NH2 (extending the carbon chain by one). Aromatic amines are made by reduction of a nitro-arene; the standard route is nitration of benzene to nitrobenzene, then reduction with tin and concentrated HCl, then neutralisation with NaOH to free the amine.

Amines also act as nucleophiles, attacking acyl chlorides and anhydrides to give amides — the key step in peptide-bond formation.

A common pitfall is to assume aromatic amines are stronger bases than aliphatic — the delocalisation argument reverses this. Another is to forget that the nitrile reduction extends the chain by one carbon, a synthetically powerful trick. See the amines lesson.

Amino Acids, Proteins and DNA

Amino acids have the general structure H2N-CHR-COOH. The amino group is basic; the carboxylic acid is acidic. At intermediate pH (around the isoelectric point, typically pH 5-6 for neutral side chains) the molecule exists as a zwitterion H3N+-CHR-COO-, with no net charge. Below the isoelectric point both groups protonate to give H3N+-CHR-COOH (cation); above it both deprotonate to give H2N-CHR-COO- (anion). The pH-dependent charge underpins electrophoresis as a separation technique.

The α-carbon of every amino acid except glycine is a chiral centre. Naturally occurring amino acids are almost exclusively the L (S) enantiomer — a fact that connects amino-acid chemistry to optical isomerism (see asymmetric synthesis below).

Proteins are condensation polymers of amino acids linked by peptide bonds -CO-NH-, formed by elimination of water between the carboxylic acid of one residue and the amine of the next. Hydrolysis with hot 6 M HCl breaks proteins back into their constituent amino acids, which can then be identified by paper or thin-layer chromatography and visualised with ninhydrin spray.

DNA is a condensation polymer of nucleotides, each comprising a deoxyribose sugar, a phosphate group and a nitrogenous base (adenine, thymine, guanine, cytosine). The 1953 double-helix model was published by Watson and Crick using X-ray diffraction data measured by Franklin. The double helix is held together by hydrogen bonds between complementary base pairs — adenine with thymine (two H-bonds) and guanine with cytosine (three H-bonds). Cisplatin is an anti-cancer drug that binds to DNA, kinking the helix and preventing replication; the AQA spec asks students to recognise its square-planar Pt(II) structure and its binding to N7 of guanine.

A common pitfall is to draw the zwitterion at the wrong pH, or to invert the protonation states above and below the isoelectric point. See the amino acids, proteins and DNA lesson.

Condensation Polymers: Polyesters and Polyamides

A condensation polymer forms by repeated condensation between two functional groups, eliminating a small molecule (usually water or HCl) at each step. Two examinable classes are polyesters and polyamides.

Polyesters form between a dicarboxylic acid and a diol. The archetype is poly(ethylene terephthalate) (PET, Terylene), made from terephthalic acid and ethane-1,2-diol. Each link is an ester group -COO-; for every link, one molecule of water leaves.

Polyamides form between a dicarboxylic acid and a diamine. The classics are nylon-6,6 (hexanedioic acid + hexane-1,6-diamine) and Kevlar (terephthalic acid + benzene-1,4-diamine, with a rigid aromatic backbone for exceptional tensile strength). Carothers, at DuPont in the 1930s, developed the first commercial nylons.

Polyesters and polyamides are both hydrolysable, unlike addition polymers (polythene, PVC) which have an inert C-C backbone. This makes condensation polymers biodegradable in principle.

A common pitfall is to draw the repeat unit with the wrong number of fragments — one of each monomer per repeat unit, with eliminated waters not shown. See the condensation polymers lesson.

Organic Synthesis: Reaction Pathways

By the end of the A-Level, students should be able to plan a synthesis from a given starting material in three to five steps. AQA examiners present these as a flow diagram with empty boxes (reagent, conditions and intermediate at each step), or as a free-form essay.

A working toolkit covers about thirty named transformations. From halogenoalkanes: nucleophilic substitution with OH-, CN-, NH3, alkoxide; elimination with hot ethanolic KOH. From alcohols: oxidation with K2Cr2O7/H+; dehydration with concentrated H2SO4. From aldehydes/ketones: reduction with NaBH4; addition with HCN. From carboxylic acids: esterification with alcohol/H2SO4; conversion to acyl chloride with PCl5 or SOCl2. From acyl chlorides: reaction with alcohol, amine or ammonia. From nitriles: hydrolysis to carboxylic acid; reduction to amine. From benzene: nitration, halogenation, Friedel-Crafts acylation; reduction of nitrobenzene to phenylamine.

A planning strategy that works for almost every question: compare carbon skeletons of starting material and target; compare functional groups; work backwards from the target, choosing the last step first (informal retrosynthesis); check each intermediate is stable.

A common pitfall is to nitrate aniline directly — the NH2 is too powerful an activator and gives over-nitration. Protect as the amide first, nitrate, then hydrolyse. See the synthesis pathways lesson.

Multi-Step and Asymmetric Synthesis

The final section pulls together stereochemistry and synthesis. Optical isomerism arises whenever a molecule has a chiral centre — a tetrahedral carbon with four different substituents. The two mirror-image forms are enantiomers; they rotate plane-polarised light by equal angles in opposite directions. A 50:50 mixture is a racemic mixture with zero net rotation. Pasteur first resolved a racemate by hand-picking tartrate crystals in 1848. The R/S nomenclature was developed by Cahn, Ingold and Prelog.

In drug chemistry, the two enantiomers can have radically different biological effects. Thalidomide, prescribed in the late 1950s, was sold as a racemate; one enantiomer was a sedative, the other teratogenic, and in vivo racemisation meant that even pure enantiomer would interconvert. Ibuprofen is also sold as a racemate, but the inactive enantiomer is metabolised to the active form, so the racemate is acceptable.

These examples motivate asymmetric synthesis — making one enantiomer preferentially using a chiral catalyst or auxiliary that biases the transition state. The 2001 Nobel Prize went to Knowles, Noyori and Sharpless for asymmetric hydrogenation and oxidation catalysts; AQA asks students to recognise that such catalysts exist as an active area of pharmaceutical chemistry, without memorising specifics.

A common pitfall is to mark a carbon as chiral when it has only three different substituents (one repeated) — check all four. Another is to claim that a racemic mixture is optically active. See the multi-step and asymmetric synthesis lesson.

Common Mark-Loss Patterns

• Drawing curly arrows that point the wrong way, or with the wrong number per step.
• Forgetting the Lewis-acid catalyst in aromatic substitution.
• Writing addition rather than substitution products with benzene.
• Claiming aromatic amines are stronger bases than aliphatic ones.
• Failing to identify HCN addition products as racemic.
• Mis-drawing the zwitterion or its protonation behaviour with pH.
• Confusing addition polymers with condensation polymers.
• Direct nitration of aniline without protecting the amine.
• Marking carbons as chiral when only three substituents differ.
• Writing one molecule of NH3 with an acyl chloride instead of two.

How to Revise This Topic

• Draw twenty curly-arrow mechanisms a week — nitration, bromination, Friedel-Crafts acylation, esterification, acyl-chloride hydrolysis, nucleophilic addition of HCN, NaBH4 reduction. Speed matters at A2.
• Build a synthesis-toolkit deck. One card per transformation: reagent, conditions, product type, mechanism class. Aim for thirty cards by mock season.
• Practise the four standard distinguishing tests for aldehyde, ketone, carboxylic acid, alcohol, alkene — every Paper 3 has at least one.
• Drill polymer repeat units. Twenty drawings until the convention is automatic.
• Memorise the acidity ordering carboxylic acid > phenol > water > alcohol and the basicity ordering aliphatic amine > ammonia > aromatic amine.
• Use the LearningBro practice quizzes under timed conditions and the AI tutor for mechanism feedback.

Linking to Other Topics

Organic advanced builds on the organic foundations curly-arrow vocabulary — nucleophilic substitution, electrophilic addition and free-radical mechanisms all reappear. Identification problems use IR (for C=O around 1700 cm^-1, broad O-H of carboxylic acid, sharp N-H of amine) and 1H and 13C NMR from analytical chemistry. The acidity of carboxylic acids and amino acids is exactly the Ka chemistry of acids and buffers. Benzene's stability comes from the delocalised π system you met in bonding. Almost every Paper 2 question rewards students who can move fluently between these viewpoints.

Final Word

Organic advanced looks intimidating because it adds aromatic chemistry, amines, biological molecules, polymers and asymmetric synthesis to an already substantial foundations toolkit. In practice the section reduces to about thirty reagent-product transformations, six curly-arrow mechanisms, four distinguishing tests, two polymer types, and a small but important stereochemistry vocabulary. Drill them until each is automatic, then practise multi-step synthesis questions until you can plan a five-step route in under five minutes. The full LearningBro Organic Chemistry Advanced course walks through every sub-topic with worked mechanisms, synthesis exercises and AI tutor feedback. Get this section fluent and Paper 2 becomes a straightforward exercise in matching mechanisms to questions.