Haloalkanes and Haloarenes - Physical and chemical properties

Physical Properties: Boiling points of alkyl halides follow the order $R-I > R-Br > R-Cl > R-F$ due to the increase in $van\ der\ Waals$ forces with molecular mass. Among isomers, branching decreases the surface area, thus decreasing the boiling point.

Solubility: Haloalkanes are polar but are only sparingly soluble in water because they cannot form hydrogen bonds with water molecules. They are soluble in organic solvents.

$S_N1$ Mechanism: A two-step nucleophilic substitution where the rate-determining step is the formation of a carbocation intermediate ($Rate = k[RX]$). Reactivity order: $3^\circ > 2^\circ > 1^\circ$. It is favored by polar protic solvents.

$S_N2$ Mechanism: A single-step process involving the simultaneous attack of the nucleophile and departure of the leaving group through a transition state ($Rate = k[RX][Nu^-]$). Reactivity order: $CH_3X > 1^\circ > 2^\circ > 3^\circ$ due to steric hindrance.

Saytzeff's Rule: In dehydrohalogenation reactions, the major product is the alkene which has a greater number of alkyl groups attached to the doubly bonded carbon atoms (more substituted alkene).

Chemical Properties of Haloarenes: Haloarenes are less reactive towards nucleophilic substitution compared to haloalkanes due to resonance (partial double bond character of $C-X$ bond), $sp^2$ hybridization of carbon, and instability of phenyl cation.

Electrophilic Substitution in Haloarenes: Halogens are deactivating but ortho- and para-directing due to $+M$ effect (resonance) despite their $-I$ effect.

Wurtz-Fittig and Fittig Reactions: Reaction of aryl halides with alkyl halides and sodium gives alkyl-substituted arenes (Wurtz-Fittig), while aryl halides reacting together give diphenyl (Fittig).