Reaction Mechanisms · Molecular Animation

3D animations of 19 reaction mechanisms, step by step: curved arrows show electron flow, dashed bonds show transition states and ¹⁸O traces esterification. Covers high-school organic chemistry, ionic reactions, redox and university mechanisms.

Subject: Chemistry · Level: High school, University · Topics: Esterification, Isotope tracing, Electron transfer, Mechanisms

Chapters

Esterification

CH₃COOH + CH₃CH₂¹⁸OH ⇌ CH₃CO¹⁸OCH₂CH₃ + H₂O

A fragrant oily liquid (ethyl acetate) appears on the saturated sodium carbonate solution. Concentrated sulfuric acid acts as catalyst and dehydrating agent.

Base hydrolysis of an ester

CH₃COOCH₂CH₃ + OH⁻ → CH₃COO⁻ + CH₃CH₂OH

The oily layer gradually disappears. Under basic conditions hydrolysis goes to completion; for fats this is called saponification and is used to make soap.

Bromine addition to ethylene

CH₂=CH₂ + Br–Br → CH₂Br–CH₂Br

The red-brown bromine colour fades quickly. This distinguishes ethylene from methane.

Addition polymerisation of ethylene

n CH₂=CH₂ → –[CH₂–CH₂]ₙ–

The product is polyethylene, a common plastic used for cling film and food bags.

Chlorination of methane

CH₄ + Cl₂ → CH₃Cl + HCl

The yellow-green colour fades, oily drops appear on the tube wall and the liquid level rises. CH₂Cl₂, CHCl₃ and CCl₄ also form.

Catalytic oxidation of ethanol

2CH₃CH₂OH + O₂ →(Cu) 2CH₃CHO + 2H₂O

The copper wire turns black in the flame (forming CuO), then red again when dipped into ethanol, with a pungent smell (acetaldehyde). Copper is the catalyst.

Dehydration of ethanol

CH₃CH₂OH →(conc. H₂SO₄, 170 ℃) CH₂=CH₂↑ + H₂O

The gas decolourises bromine water and acidified potassium permanganate. The temperature must rise quickly to 170 ℃; at 140 ℃ the main product is diethyl ether.

Bromination of benzene

C₆H₆ + Br₂ →(FeBr₃) C₆H₅Br + HBr

Colourless oily bromobenzene forms (brown from dissolved bromine), and white fumes appear at the tube outlet (HBr meeting water vapour). Benzene does not decolourise bromine water.

Neutralisation

H₃O⁺ + OH⁻ → 2H₂O （H⁺ + OH⁻ = H₂O）

Add hydrochloric acid drop by drop to NaOH solution containing phenolphthalein; when the pink just disappears, the acid and base exactly neutralise. Na⁺ and Cl⁻ take no part.

Silver chloride precipitate

Ag⁺ + Cl⁻ → AgCl↓

A white precipitate forms at once and does not dissolve in dilute nitric acid. This is a common test for Cl⁻. Na⁺ and NO₃⁻ are spectator ions.

Zinc displaces copper

Zn + Cu²⁺ → Zn²⁺ + Cu

Red copper deposits on the zinc and the blue solution fades. At heart, electrons move from Zn to Cu²⁺.

Sodium and water

2Na + 2H₂O → 2Na⁺ + 2OH⁻ + H₂↑

Sodium floats, melts into a ball, darts around and hisses; the solution with phenolphthalein turns pink.

Combustion of methane

CH₄ + 2O₂ → CO₂ + 2H₂O ΔH = −890 kJ/mol

A pale blue flame releases a lot of heat; droplets form inside a dry, cold beaker held over the flame, and limewater poured in turns cloudy.

Hydrogen burning in chlorine

H₂ + Cl₂ → 2HCl ΔH = −183 kJ/mol

It burns quietly with a pale flame, and white mist appears at the mouth of the bottle (HCl forming droplets of hydrochloric acid with water vapour).

Thermite reaction

2Al + Fe₂O₃ →(high temp.) Al₂O₃ + 2Fe

A violent reaction throws sparks and releases great heat; the iron produced falls molten into the sand. It is used to weld rails.

SN2 reaction

HO⁻ + CH₃Br → CH₃OH + Br⁻

Rate = k[CH₃Br][OH⁻], second order. A chiral carbon inverts its configuration (Walden inversion), like an umbrella flipped inside out by the wind.

SN1 reaction

(CH₃)₃CBr + H₂O → (CH₃)₃COH + HBr

Rate = k[(CH₃)₃CBr], first order, depending only on the substrate. The carbocation is planar, so the nucleophile can attack from either face and a chiral substrate racemises.

E2 elimination

HO⁻ + CH₃CH₂Br → CH₂=CH₂ + H₂O + Br⁻

One concerted step. The β-H being removed and the leaving Br must be anti-periplanar (dihedral angle 180°). The product is an alkene.

Full esterification mechanism

CH₃COOH + CH₃CH₂¹⁸OH ⇌(H⁺) CH₃CO¹⁸OEt + H₂O

Fischer esterification: an addition–elimination mechanism through a tetrahedral intermediate. H⁺ is used in the first step and regenerated in the last, so it is a catalyst.

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