Strongly exothermic – the basis of fuels. CO₂ is a greenhouse gas. Fuels are separated by fractional distillation (boiling point rises with chain length because of stronger London forces).

CO is toxic (binds irreversibly to haemoglobin); soot is particulate carbon.

Thermal (high T ≈ 700–1200 K, high pressure): free-radical, mainly alkenes. Catalytic (zeolite, ≈ 720 K, slight pressure): branched alkanes, cycloalkanes and arenes for motor fuels. e.g. C₁₀H₂₂ → C₈H₁₈ + C₂H₄. Alkenes are the feedstock for polymers.

Br₂ behaves similarly. Further substitution gives CH₂Cl₂, CHCl₃, CCl₄; use excess alkane to favour the mono-substituted product. Mechanism on the Mechanisms sheet.

Sulfur impurities burn to SO₂ (acid rain). Unburnt hydrocarbons, CO and NO_x are removed by the converter.

Also used to harden unsaturated vegetable oils (margarine).

Orange / brown bromine water → colourless. In bromine water some 2-bromoethanol (Br–CH₂–CH₂–OH) also forms because water competes as the nucleophile.

The major product goes via the more stable secondary carbocation (two electron-releasing alkyl groups). HCl and HI react similarly. Rule of thumb: H adds to the C that already has more H.

Exothermic and reversible; fewer gas moles on the right. High pressure favours yield but is costly and promotes polymerisation, and high T raises the rate but lowers the yield, so 300 °C is a compromise. Unreacted ethene is recycled.

Primary: SN2. Tertiary: SN1. Water alone also works but slowly (R–X + H₂O → R–OH + HX). Rate: C–I > C–Br > C–Cl – set by bond enthalpy (the weakest C–X bond breaks fastest), not by polarity.

Warm (≈ 50 °C) the halogenoalkane with ethanol and AgNO₃(aq). Water is the nucleophile, and the halide ion released precipitates: Ag⁺(aq) + X^–(aq) → AgX(s). Precipitate forms fastest with iodo- (yellow), then bromo- (cream), then chloro- (white). The ethanol makes the halogenoalkane and water miscible. Control the volume, concentration and temperature, and time the appearance of the precipitate.

Solvent must be ethanol – aqueous KCN would also give some alcohol. The nitrile can then be hydrolysed to an acid or reduced to an amine.

The amine product is still nucleophilic: with less NH₃ it reacts further to give secondary and tertiary amines and finally a quaternary ammonium salt, so use a large excess of NH₃.

OH^– acts as a base. Ethanolic, hot and concentrated conditions favour elimination; aqueous conditions favour substitution.

Orange (Cr₂O₇^2–) → green (Cr³⁺). The aldehyde has a lower boiling point (no hydrogen bonding), so it distils out before further oxidation. Cr₂O₇^2– + 14H⁺ + 6e^– → 2Cr³⁺ + 7H₂O.

Reflux returns the aldehyde to the hot oxidant until it is fully oxidised.

Tertiary alcohols do not oxidise (no H on the C–OH carbon): the solution stays orange.

Reversible – use excess of one reagent or remove water to raise the yield. Esters have a sweet, fruity smell.

PCl₅ test: steamy white HCl fumes (dry sample only). Very concentrated H₂SO₄ oxidises HBr to Br₂, so use ≈ 50% acid.

Purification: separating funnel → wash with NaHCO₃(aq) (vent the CO₂) → wash with water → dry (anhydrous Na₂SO₄ or CaCl₂) → decant → distil and collect at ≈ 51 °C.

Purified by fractional distillation. Compared with hydration it is slow and batch-based, and gives dilute impure ethanol, but it uses renewable resources and low energy.

Aldehyde → 1° alcohol; ketone → 2° alcohol. NaBH₄ reduces only C=O (aldehydes and ketones). LiAlH₄ is stronger (also acids, esters, amides and nitriles) and reacts violently with water, so it must be used in dry ether.

Adds one carbon. HCN is very toxic, so it is generated in situ from KCN and acid. The product is a racemic mixture, because the planar C=O is attacked equally from both faces.

Yellow / orange / red precipitate with any aldehyde or ketone (not acids or esters). Recrystallise it and measure the melting point; compare with data tables to identify the carbonyl compound.

Silver mirror on warming in a water bath (≈ 50–60 °C); ketones: no change. Reagent: AgNO₃ + NaOH → Ag₂O, then add just enough dilute NH₃ to dissolve it. The Ag⁺ is reduced (Ag⁺ + e^– → Ag), so the aldehyde is oxidised.

Blue solution → brick-red precipitate on warming (aliphatic aldehydes); ketones: no change.

Pale yellow precipitate of CHI₃, antiseptic smell (I₂ + NaOH(aq), warm). Positive for methyl ketones, ethanal, ethanol and CH₃CH(OH)–R (oxidised in situ).

Effervescence with carbonates / hydrogencarbonates (CO₂ turns limewater milky) – the standard test for –COOH. Carboxylic acids are weak acids (partial dissociation).

NaBH₄ is not strong enough to reduce carboxylic acids.

Steamy fumes of HCl. Esterification of acids with alcohols: see Alcohols.

Very reactive: the C is strongly δ+ (bonded to both O and Cl) and Cl^– is a good leaving group. Mechanism on the Mechanisms sheet. Amine + acyl chloride gives an N-substituted amide.

Slower, cheaper, safer and less corrosive than acyl chlorides, and no HCl is produced, so it is preferred industrially. The by-product is ethanoic acid.

Purify: add cold water to crystallise → vacuum filter → recrystallise from the minimum hot solvent (ethanol / water) → dry. Purity: sharp melting point at ≈ 135 °C; or a FeCl₃ test (purple if phenolic salicylic acid remains).

Acid hydrolysis is reversible (excess water). Alkaline hydrolysis is irreversible and goes to completion giving the carboxylate salt; acidify to obtain the free acid. Uses of esters: flavourings, perfumes, solvents.

Acid hydrolysis (H₂O / H⁺) gives glycerol + three fatty acids. Saturated chains pack closely (higher m.p.); C=C chains are kinked (lower m.p.) and can be hydrogenated (Ni) to harden the fat.

Biodiesel is a mixture of methyl esters of fatty acids from plant oils (a renewable fuel); the glycerol is a by-product.

Alkaline hydrolysis gives the carboxylate (acidify to obtain the acid) and NH₃ gas.

The acid gives the phenylammonium ion (C₆H₅NH₃⁺); NaOH then liberates the free amine. Other routes to amines: halogenoalkane + excess NH₃, and nitrile reduction (above).

The N lone pair accepts H⁺. Alkylamines are stronger bases than NH₃ (alkyl groups push electron density onto N). Phenylamine is a weaker base because the lone pair is partly delocalised into the ring.

Repeated substitution gives 3° amines, then quaternary ammonium salts. Those with a long alkyl chain, e.g. CH₃(CH₂)₁₅N⁺(CH₃)₃Br^–, are cationic surfactants (fabric softeners, hair conditioners). Amines + acyl chlorides / anhydrides: see the Acyl chlorides sheet.

NH₃ released on alkaline hydrolysis turns damp red litmus blue.

Amino acids are crystalline, soluble in water and have high melting points (ionic character). All except glycine are chiral (the two enantiomers of alanine are mirror images):

Hydrolysis: 6 mol dm^–3 HCl, reflux ≈ 24 h → amino acids (as ammonium salts). They are separated and identified by TLC / paper chromatography, sprayed with ninhydrin (purple / violet spots) and compared by R_f.

HNO₂ is made in situ from NaNO₂ + HCl. Keep below 10 °C or the diazonium ion decomposes.

Orange / yellow-orange precipitate (with naphthalen-2-ol: red-orange). The azo group (–N=N–) joins the two rings in an extended delocalised system (chromophore) that absorbs visible light, so the compound is coloured.

Electrophile: HNO₃ + 2H₂SO₄ → NO₂⁺ + H₃O⁺ + 2HSO₄⁻ · Catalyst regenerated: H⁺ + HSO₄⁻ → H₂SO₄

Above ~55 °C, further nitration gives dinitrobenzene. Nitrobenzene is a pale yellow oil that is reduced to phenylamine (Nitrogen sheet).

Electrophile: Br₂ + FeBr₃ → Br⁺ + FeBr₄⁻ · Catalyst regenerated: H⁺ + FeBr₄⁻ → FeBr₃ + HBr

Chlorination uses Cl₂ with AlCl₃ or FeCl₃. Benzene does not react with bromine water (no catalyst; the electron density in the ring is too low to polarise Br₂).

Electrophile: CH₃COCl + AlCl₃ → CH₃CO⁺ + AlCl₄⁻ · Catalyst regenerated: H⁺ + AlCl₄⁻ → AlCl₃ + HCl

Forms a C–C bond to give an aromatic ketone. The AlCl₃ needs anhydrous conditions.

Electrophile: R⁺ from RCl + AlCl₃. Polysubstitution can occur, since the alkylbenzene is more reactive than benzene.

Nitrobenzene → phenylamine (Sn / conc. HCl, reflux; then NaOH) · Phenylamine → diazonium (NaNO₂ / HCl, 0–10 °C) · Diazonium + phenol → azo dye (alkaline, < 10 °C) – all on the Nitrogen sheet.

White precipitate with bromine water. Phenol is a weak acid: it reacts with NaOH but not with NaHCO₃. The O lone pair delocalises into the ring, making phenol more reactive than benzene (no catalyst needed, and substitution at the 2, 4 and 6 positions).

Phenol is too unreactive to form esters directly with carboxylic acids, so an acyl chloride (or an acid anhydride, as in the aspirin preparation) is used.

To draw the repeat unit: open the C=C, make it a single bond, and extend a bond from each end through the brackets. Properties: unreactive, non-polar and non-biodegradable because the C–C and C–H bonds are strong and non-polar.

Ester links; the by-product is water. A dicarbonyl dichloride can be used in place of the diacid (HCl is produced instead).

A biodegradable polyester from renewable resources (hydrolysable ester links).

With hexanedioic acid instead of the diacyl dichloride, 2n H₂O is eliminated (needs heat). The amide links hydrogen-bond between chains, giving strong fibres.

Very strong: rigid aromatic rings and extensive hydrogen bonding between the amide groups hold the chains together, giving high tensile strength and heat resistance (body armour, tyre cord).

Initiation – UV light causes homolytic fission of Cl–Cl. Two fishhook arrows leave the bond, one to each Cl.

Propagation – a radical reacts with a molecule and a new radical is formed, so the chain continues. Cl• takes H (one arrow from the radical, one from the C–H bond).

Termination – two radicals combine (each contributes one electron to the new bond) and no radical is left.

Step 1 – the π bond (electron pair) attacks the δ+ H of H–Br. The H–Br bond breaks heterolytically and both electrons go to Br, giving a carbocation and Br^–.

Step 2 – a lone pair on Br^– attacks C⁺.

Propene (Markovnikov). The secondary carbocation is stabilised by two electron-releasing alkyl groups, so it is more stable and forms in greater amount; it gives the major product.

Minor route. The same arrows, but H adds to the other carbon, giving the less stable primary carbocation.

The π electrons of the alkene induce a dipole in Br–Br. The π bond attacks Br^δ+, the Br–Br bond breaks heterolytically (electrons go to Br^δ–) and a carbocation forms.

Br^– then attacks C⁺ using a lone pair.

One step, second order (rate = k[RX][OH^–]). The lone pair on OH^– attacks the δ+ carbon from the side opposite the Br (back-side attack), so the nucleophile is drawn opposite the C–Br bond. As the new C–O bond forms, the C–Br bond breaks and both electrons go to Br. The transition state has five groups round C with partial bonds (dotted). A chiral centre is inverted.

Step 1 (slow, rate-determining) – the C–Br bond breaks heterolytically and both electrons go to Br, giving a planar carbocation. Rate = k[RX].

Step 2 (fast) – a lone pair on OH^– (or H₂O) attacks C⁺ from either face, so a chiral centre gives a racemic mixture.

OH^– acts as a base. Its lone pair takes an H from the carbon next to C–Br, the C–H electrons form the C=C, and the C–Br electrons leave with Br^–. All three arrows belong to one step.

HCN. A lone pair on CN^– (on carbon) attacks the δ+ carbon. The C=O π electrons move onto O, giving an alkoxide intermediate. The planar C=O is attacked from both faces, so the product is racemic.

O^– then takes H⁺ from HCN (or H₂O) to form the hydroxynitrile and regenerate CN^–.

NaBH₄ reduction. The hydride ion H^– (from BH₄^–) acts as the nucleophile.

The alkoxide is then protonated by water.

Addition – the lone pair on N attacks the δ+ carbon and the C=O π electrons move onto O, giving a tetrahedral intermediate.

Elimination – a lone pair on O^– re-forms C=O and the C–Cl electrons leave with Cl^–.

A second NH₃ removes H⁺ from N (the N–H electrons stay on N). Water, alcohols and amines react in the same way.

Electrophile: HNO₃ + 2H₂SO₄ → NO₂⁺ + H₃O⁺ + 2HSO₄⁻

Step 1 – a pair of π electrons from the ring (arrow starts inside the circle) attacks the N of NO₂⁺. Aromaticity is lost and the positive charge is delocalised over the other five carbons (the partial circle with +).

Step 2 – HSO₄^– removes H⁺ using a lone pair; the C–H bond electrons return to the ring to restore the delocalised π system. This regenerates the H₂SO₄ catalyst.

Electrophile: CH₃COCl + AlCl₃ → CH₃CO⁺ + AlCl₄⁻

Bromination uses Br₂ + FeBr₃ → Br⁺ + FeBr₄^–. Alkylation uses RCl + AlCl₃ → R⁺ + AlCl₄^–. Both follow the same two steps and the same arrows.