Hydrocarbons are classified as alkanes (Cₙ$H_{2}$ₙ₊{2}, saturated, $sp^{3}$), alkenes (Cₙ$H_{2}$ₙ, one C=C, $sp^{2}$), and alkynes (Cₙ$H_{2}$ₙ₋{2}, one C≡C, sp), each with distinct hybridization and reactivity.

In alkane conformational analysis using Newman projections, the anti conformation of butane (180° dihedral) is most stable, and the fully eclipsed conformation (0° dihedral) is least stable because both methyl groups eclipse each other.

Stability order for butane is anti > gauche > eclipsed > fully eclipsed, encoded by the mnemonic "A Gentle Evening Falls."

Free radical halogenation of alkanes proceeds in three steps — initiation ($X_{2}$ → 2X• by UV/heat), propagation (chain), and termination (radical combination) — with H-abstraction selectivity following 3° > 2° > 1°.

$Br_{2}$ is the most selective halogen in free radical halogenation because Br• has higher activation energy for H abstraction, making it highly discriminating between C–H bond types.

Markovnikov's rule governs ionic electrophilic addition of HX to alkenes: H adds to the carbon with more H atoms, forming the more stable carbocation intermediate.

Anti-Markovnikov addition (Kharasch effect) occurs ONLY with HBr + organic peroxide — not with HCl (endothermic radical step) or HI (premature termination) — giving the regioisomeric product.

Reductive ozonolysis ($O_{3}$/Zn/$H_{2}$O) cleaves the C=C bond, converting each doubly-bonded carbon to a carbonyl group (aldehyde if the carbon has H; ketone if it has no H).

Terminal alkynes are more acidic than alkenes and alkanes because the sp-hybridized C–H bond has 50% s-character, and the resulting acetylide anion is stabilized by this high electronegativity of the sp carbon.

Internal alkynes are selectively reduced to cis-alkenes by Lindlar's catalyst (syn-addition) or to trans-alkenes by Na/liquid $NH_{3}$ (anti-addition via radical anion mechanism), with complete reduction to alkane requiring undeactivated $H_{2}$/Pd–C.