Chemistry · Ch 12 — Organic Chemistry – Some Basic Principles and Techniques

Summary

Hybridisation of carbon: $sp^3$ (tetrahedral, $109.5^\circ$ ), $sp^2$ (trigonal planar, $120^\circ$ ), $sp$ (linear, $180^\circ$ ). Bond length order: $sp < sp^2 < sp^3$ .
IUPAC nomenclature: Select the longest continuous carbon chain as the parent. Number from the end nearest the first substituent. Use prefixes (fluoro-, chloro-, bromo-, iodo-), suffixes (-ane, -ene, -yne), and locants. For functional groups, the principal group gets the lowest number and is cited as a suffix (e.g., -ol, -al, -one, -oic acid).
Isomerism: Structural (chain, position, functional, metamerism) and stereoisomerism (geometrical — cis/trans in alkenes; optical — chiral carbon with four different groups, enantiomers rotate plane-polarised light equally but oppositely).
Electron displacement effects: Inductive effect ( $-I$ groups withdraw, $+I$ groups donate; permanent, through sigma bonds), resonance (delocalisation of $\pi$ electrons; stabilises the molecule), and hyperconjugation (delocalisation of $\sigma$ C–H electrons into an adjacent empty or $\pi$ orbital; increases stability).
Reaction intermediates: Carbocations ( $sp^2$ , planar, electron-deficient; stability: $3^\circ > 2^\circ > 1^\circ > \text{CH}_3^+$ ), carbanions ( $sp^3$ , pyramidal, electron-rich; stability: $1^\circ > 2^\circ > 3^\circ$ ), free radicals ( $sp^2$ , planar, unpaired electron; stability: $3^\circ > 2^\circ > 1^\circ > \text{CH}_3\bullet$ ).
Purification techniques: Sublimation (for solids that vaporise without melting), crystallisation (based on solubility differences), distillation (for liquids with different boiling points; fractional distillation for close-boiling mixtures), steam distillation (for steam-volatile, water-immiscible compounds), differential extraction (using a solvent immiscible with water), and chromatography (adsorption or partition; $R_f = \frac{\text{distance moved by solute}}{\text{distance moved by solvent front}}$ ). …

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