Organic Chemistry: Basic Principles and Techniques
Unit 12 tests IUPAC nomenclature, electronic effects, reactive intermediates, reaction classification and the purification and analysis of organic compounds.
Core rules
- IUPAC naming: identify the longest carbon chain containing the principal functional group, number to give that group the lowest locant, then name substituents alphabetically.
- Isomerism includes chain, position, functional, geometrical and optical isomerism.
- Bond cleavage is homolytic (radicals) or heterolytic (carbocations and carbanions).
- Electronic effects: inductive (σ-bond transmission), electromeric (π-electron shift), resonance and hyperconjugation. Carbocation stability follows tertiary > secondary > primary > methyl.
- Reaction types: substitution, addition, elimination and rearrangement; reagents are nucleophiles or electrophiles.
- Purification: distillation, fractional distillation, steam distillation, sublimation, crystallisation and chromatography.
- Detection of N, S and halogens uses sodium fusion (Lassaigne's test); Carius method estimates halogens and sulfur; Kjeldahl's method estimates nitrogen.
Worked example
Name CH₃–CH(CH₃)–CH₂–CHO. The principal group is –CHO, so the chain must include it and numbering starts at the aldehyde carbon: C-1 is CHO, C-2 is CH₂, C-3 carries the methyl branch, C-4 is CH₃. The parent chain has four carbons (butanal), with a methyl at C-3, giving 3-methylbutanal.
Traps
- Numbering must give the principal functional group the lowest number, not always the nearest branch.
- Electromeric effect operates only in the presence of an attacking reagent; inductive effect is permanent.
- A tertiary carbocation is stabilised by hyperconjugation and inductive donation, not by resonance unless adjacent to a π system.
- In Lassaigne's test, nitrogen is detected as Prussian blue and halogens as silver halides.
- Chromatography separates by differential adsorption or partition, not by boiling point.