Curly-arrow mechanisms – nucleophilic addition and addition–elimination
ChemistryOrganic ChemistryAges 17–18
Use it with your class: students open it from a link or a QR code, with no account needed.
Next in Organic Chemistry
A 2D curly-arrow builder: drag arrows from lone pairs and bonds to atoms, and the tool works out the new bonds, electron counts and charges, then checks them against the next intermediate. Guided mechanisms cover HCN addition to aldehydes and ketones, addition–elimination of acyl chlorides and acid anhydrides (aspirin included), and the aldol, Cannizzaro and haloform reactions; free play accepts radical, nucleophilic and electrophilic steps.
Lesson: Reaction mechanisms with curly arrows: carbonyl compounds and acyl derivatives
What it shows
Curly arrows are the bookkeeping of organic chemistry: each one moves an electron pair from a lone pair or a bond to the atom that receives it, and a fish-hook moves a single electron. In nucleophilic addition, CN⁻ attacks the δ+ carbon of a flat C=O group from either face, so ethanal gives a racemic hydroxynitrile. Acyl chlorides and acid anhydrides react by addition–elimination, giving acids, esters and amides. The aldol, Cannizzaro and haloform reactions show carbanions and hydride ions at work.
How to use
In Guided mechanisms, choose a Mechanism (and the Carbonyl compound or Nucleophile). Drag from a lone pair or a bond to an atom to draw an arrow, then press Check step; red arrows do not fit. Hint shows dashed arrows. After the HCN mechanism, React 1000 molecules counts both faces. In Free play, choose the Starting species, pick Curly arrow or Fish-hook, and press Apply arrows.
Parameters you can change
- Screen Guided mechanisms, Free play
- Mechanism Nucleophilic addition of HCN, Addition–elimination: acyl chloride, Addition–elimination: acid anhydride, Aldol addition and condensation, Cannizzaro reaction, Haloform (iodoform) reaction
- Carbonyl compound Ethanal CH₃CHO, Propanone CH₃COCH₃
- Nucleophile Water H₂O, Ethanol C₂H₅OH, Ammonia NH₃, Methylamine CH₃NH₂, 2-Hydroxybenzoic acid (aspirin)
- Starting species Ethene + HBr, Methane + Cl₂ (UV), Bromoethane + OH⁻, Propanone + CN⁻ + HCN
- Show δ+ and δ−
Questions to explore
- Why does CN⁻ addition to ethanal give a racemic mixture, but addition to propanone gives no enantiomers?
- Which bond breaks in the elimination step for an acyl chloride, and which for an acid anhydride?
- In the Cannizzaro reaction, which methanal molecule is oxidised and which is reduced?
