Organic Nitrogen Compounds - Formula Sheet

Amine Dissociation Equilibrium

The basic strength of an amine in water is determined by its base dissociation constant: Kb = [RNH3+][OH-] / [RNH2]
pKb = -log10 Kb

Definition of Symbols

• Kb: The base dissociation constant, measuring the ionization extent of the base.
• [RNH2]: The molar concentration of the un-ionized amine base.
• [RNH3+]: The molar concentration of the conjugate acid formed in solution.
• [OH-]: The molar concentration of hydroxide ions.
• pKb: The logarithmic basicity index; lower pKb values correspond to stronger bases.

Henderson-Hasselbalch Equation for Buffer Solutions

For an amine-based buffer (weak base and its salt): pOH = pKb + log10 ([Conjugate Acid] / [Base])
pH = pKa + log10 ([Base] / [Acid])

Definition of Symbols

• pH: Potential of hydrogen, indicating solution acidity.
• pOH: Potential of hydroxide, indicating solution basicity (pH + pOH = 14 at 298 K).
• pKa: The logarithmic acid dissociation constant of the weak conjugate acid.
• [Base]: The molar concentration of the weak amine base.
• [Conjugate Acid]: The molar concentration of the salt/cation component in the buffer.

Alkyl Halide Nucleophilic Reactivity

Reactivity toward amines: RI > RBr > RCl

Definition of Symbols

• RI: Alkyl iodide, the most reactive due to its low carbon-halogen bond dissociation energy and excellent leaving ability.
• RBr: Alkyl bromide.
• RCl: Alkyl chloride, the least reactive in the series due to its high bond strength.

Basicity Trend of Methyl-Substituted Amines in Aqueous Medium

Basicity Order: (CH3)2NH > CH3NH2 > (CH3)3N > NH3

Definition of Symbols

• (CH3)2NH: Dimethylamine (secondary amine), which has the highest aqueous basicity due to optimal steric hindrance, solvation stability, and positive inductive effect.
• CH3NH2: Methylamine (primary amine).
• (CH3)3N: Trimethylamine (tertiary amine), which has low basicity in water despite three +I groups because steric hindrance blocks hydration.
• NH3: Ammonia, which lacks any electron-donating alkyl substituents.