Hydrocarbons

Chapter Overview

Hydrocarbons opens the organic chemistry portion of the Punjab Board intermediate curriculum, systematically organizing carbon-hydrogen compounds into aliphatic (acyclic and alicyclic) and aromatic families. The chapter begins with IUPAC nomenclature rules for alkanes and cycloalkanes, explaining the tetrahedral sp3 hybridization geometry, conformational aspects, and why non-polar sigma bonds render alkanes inert toward polar acids and bases under normal laboratory conditions.

The mechanistic foundation of organic reactions is developed through homolytic and heterolytic bond fission modes. Students explore free-radical substitution mechanisms in alkanes (chlorination and bromination), breaking down initiation, propagation, and termination steps. Transitioning to unsaturated alkenes, the presence of the exposed, electron-rich pi bond makes alkenes susceptible to electrophilic addition reactions. Students examine additions of halogens, hydrogen halides, sulfuric acid, and water, applying Markovnikov's rule supported by carbocation intermediate stabilities and alkyl group inductive effects.

The concluding modules investigate advanced organic concepts including conjugated dienes (1,2- and 1,4-additions), polymerizations, and analytical ozonolysis used to pinpoint double-bond positions in unknown olefins. In addition, the chapter categorizes structural isomerism (chain, position, functional group, metamerism, and tautomerism) and stereoisomerism (geometric cis-trans isomerism arising from restricted rotation about carbon-carbon double bonds), alongside modern organic oxidation and reduction classifications.