How organic molecules are named, drawn and react
Organic compounds are named using IUPAC rules: find the longest carbon chain, number it to give the functional group the lowest locant, then add prefixes and suffixes. Compounds with the same molecular formula but different structures are isomers. Structural isomers differ in chain, position or functional group, while stereoisomers differ in spatial arrangement, as in geometrical and optical isomers.
Electron movements explain reactivity. The inductive effect is the permanent shift of electrons along a sigma bond towards more electronegative atoms. Resonance spreads electrons over several atoms, the electromeric effect is a temporary shift in the presence of a reagent, and hyperconjugation explains the stability of carbocations and alkenes. Bonds can break homolytically to form free radicals or heterolytically to form carbocations and carbanions. Tertiary carbocations are more stable than primary ones. Reagents are electrophiles, which seek electrons, or nucleophiles, which donate them. Purification methods include crystallisation, distillation and chromatography.
Why it matters
These basics are the grammar of organic chemistry: every reaction of alcohols, aldehydes, haloalkanes and biomolecules is explained using them. Naming compounds correctly avoids dangerous mistakes in pharmacies and laboratories. Understanding isomers explains why two medicines with the same formula can act differently in the body.
Key terms
- Isomers
- Compounds with the same molecular formula but different structures or spatial arrangements.
- Inductive effect
- The permanent shift of electron density along a chain of sigma bonds.
- Carbocation
- A positively charged carbon species formed during some organic reactions.
- Electrophile
- An electron-seeking reagent that attacks regions of high electron density.