Free Radical Halogenation (Alkanes): $CH_4 + Cl_2 \xrightarrow{UV \text{ light}} CH_3Cl + HCl$
- Mixture of products, difficult to control.
Electrophilic Addition (Alkenes):
- $CH_2=CH_2 + HBr \rightarrow CH_3CH_2Br$ (Markovnikov's Rule for unsymmetrical alkenes)
- $CH_3-CH=CH_2 + HBr \rightarrow CH_3-CH(Br)-CH_3$ (Major product)
- Peroxide effect (Anti-Markovnikov): $CH_3-CH=CH_2 + HBr \xrightarrow{\text{Peroxide}} CH_3-CH_2-CH_2-Br$ (Only with HBr)
- Addition of Halogens: $CH_2=CH_2 + Br_2 \xrightarrow{CCl_4} Br-CH_2-CH_2-Br$ (Vicinal dihalide, test for unsaturation)

Finkelstein Reaction: $R-X + NaI \xrightarrow{\text{Acetone}} R-I + NaX \downarrow$ ($X = Cl, Br$)
- Used for preparing iodoalkanes.
Swarts Reaction: $R-X + AgF \rightarrow R-F + AgX \downarrow$ ($X = Cl, Br$)
- Used for preparing fluoroalkanes. Other metallic fluorides like $Hg_2F_2, CoF_2, SbF_3$ can also be used.

Electrophilic Substitution:
- $C_6H_6 + Cl_2 \xrightarrow{FeCl_3 \text{ (Lewis acid)}} C_6H_5Cl + HCl$
- $C_6H_6 + Br_2 \xrightarrow{FeBr_3} C_6H_5Br + HBr$
- Fluorination and iodination are difficult to control.
Sandmeyer Reaction: (From Diazonium Salts)
- $Ar-N_2^+Cl^- \xrightarrow{Cu_2Cl_2/HCl} Ar-Cl + N_2$
- $Ar-N_2^+Cl^- \xrightarrow{Cu_2Br_2/HBr} Ar-Br + N_2$
- Gattermann Reaction: Using Cu powder/HX for less yield.
Balz-Schiemann Reaction: For Fluorobenzene
- $Ar-N_2^+Cl^- \xrightarrow{HBF_4} Ar-N_2^+BF_4^- \xrightarrow{\Delta} Ar-F + BF_3 + N_2$

Boiling Points:
- Haloalkanes: $RI > RBr > RCl > RF$ (due to increasing size/mass, stronger van der Waals forces).
- Branching decreases boiling point.
- Haloarenes have higher boiling points than haloalkanes with same number of carbons due to greater polarity and size.
Density: $RI > RBr > RCl$. Denser than water.
Solubility: Slightly soluble in water (cannot form H-bonds with water molecules as strongly as water-water H-bonds) but soluble in organic solvents.

Nucleophile: Electron-rich species, attacks electron-deficient carbon.
$S_N2$ (bimolecular nucleophilic substitution):
- One step, concerted mechanism.
- Rate depends on concentration of both alkyl halide and nucleophile: Rate $= k[R-X][Nu^-]$
- Inversion of configuration (Walden inversion).
- Favored by $1^\circ$ alkyl halides, strong nucleophiles, aprotic polar solvents.
- Steric hindrance hinders $S_N2$: $CH_3X > 1^\circ > 2^\circ > 3^\circ$
$S_N1$ (unimolecular nucleophilic substitution):
- Two steps: 1. Formation of carbocation (slow, rate-determining). 2. Nucleophilic attack.
- Rate depends only on concentration of alkyl halide: Rate $= k[R-X]$
- Racemisation occurs (attack from both sides of planar carbocation).
- Favor