$\mathrm{HX}$ ($\mathrm{HCl, HBr, HI}$)

Adds across double/triple bonds (Markovnikov's rule).
- $\mathrm{R-CH=CH_2 \xrightarrow{HBr} R-CH(Br)-CH_3}$
Converts alcohols to alkyl halides.
- $\mathrm{R-OH \xrightarrow{HCl/ZnCl_2} R-Cl}$ (Lucas Test)

$\mathrm{PCl_3, PCl_5, SOCl_2}$ (Thionyl Chloride)

Converts alcohols to alkyl chlorides. $\mathrm{SOCl_2}$ is preferred due to gaseous byproducts.
- $\mathrm{R-OH \xrightarrow{SOCl_2} R-Cl + SO_2 + HCl}$

$\mathrm{NaI/Acetone}$ (Finkelstein Reaction)

Alkyl chlorides/bromides to alkyl iodides.
- $\mathrm{R-Cl \xrightarrow{NaI/Acetone} R-I}$ (S_N2 reaction, drives equilibrium by ppt of NaCl/NaBr)

$\mathrm{AgF, Hg_2F_2, CoF_2, SbF_3}$ (Swarts Reaction)

Alkyl chlorides/bromides to alkyl fluorides.
- $\mathrm{R-Cl \xrightarrow{AgF} R-F}$

4. Reagents for Formation of C-C Bonds / Carbonyl Chemistry

Grignard Reagent ($\mathrm{RMgX}$)
- Forms new C-C bonds.
  - $\mathrm{HCHO \xrightarrow{RMgX, then H_2O} R-CH_2OH}$ (Formaldehyde to primary alcohol)
  - $\mathrm{R'-CHO \xrightarrow{RMgX, then H_2O} R'-CH(OH)-R}$ (Aldehyde to secondary alcohol)
  - $\mathrm{R'_2C=O \xrightarrow{RMgX, then H_2O} R'_2C(OH)-R}$ (Ketone to tertiary alcohol)
  - $\mathrm{CO_2 \xrightarrow{RMgX, then H_2O} R-COOH}$ (Carbon dioxide to carboxylic acid)
$\mathrm{NaCN}$ or $\mathrm{KCN}$
- Introduces cyano group (precursor to carboxylic acids, amines).
  - $\mathrm{R-X \xrightarrow{NaCN} R-CN}$ (Alkyl halide to nitrile)
  - $\mathrm{R-CHO \xrightarrow{HCN} R-CH(OH)-CN}$ (Aldehyde to cyanohydrin)
$\mathrm{AlCl_3}$ (Anhydrous)
- Friedel-Crafts Alkylation: $\mathrm{C_6H_6 + R-X \xrightarrow{Anhy. AlCl_3} C_6H_5-R}$
- Friedel-Crafts Acylation: $\mathrm{C_6H_6 + R-COCl \xrightarrow{Anhy. AlCl_3} C_6H_5-COR}$
$\mathrm{NaOH/Dilute}$ (Aldol Condensation)
- Aldehydes/ketones with $\alpha$-hydrogens.
  - $\mathrm{2 R-CHO \xrightarrow{Dil. NaOH} R-CH(OH)-CH_2-CHO}$ ($\beta$-hydroxy aldehyde)
$\mathrm{NaOH/Conc.}$ (Cannizzaro Reaction)
- Aldehydes WITHOUT $\alpha$-hydrogens.
  - $\mathrm{2 HCHO \xrightarrow{Conc. NaOH} CH_3OH + HCOONa}$ (Disproportionation)
$\mathrm{CHCl_3/KOH}$ (Carbylamine Reaction)
- Test for primary amines.
  - $\mathrm{R-NH_2 \xrightarrow{CHCl_3/KOH} R-NC}$ (Offensive smell isocyanide)
$\mathrm{NaNO_2/HCl}$ (Nitrous Acid)
- $0-5^\circ C$: Diazotisation of primary aromatic amines.
  - $\mathrm{Ar-NH_2 \xrightarrow{NaNO_2/HCl, 0-5^\circ C} Ar-N_2^+Cl^-}$ (D