Nitrogen Containing Organic Compounds: Concepts to Remember

1. Amines:

• Nomenclature: RNH2 (primary), R2NH (secondary), R3N (tertiary).
• Classification: Primary, secondary, tertiary.
• Preparation:
• From alkyl halides: R-X + NH3 → R-NH2 + HX
• From ammonia: R-X + 2 NH3 → R-NH2 + NH4X
• From nitro compounds: R-NO2 + 6 [H] → R-NH2 + 2 H2O
• From amides: R-CONH2 + H2O → R-NH2 + CO2
• Physical and chemical properties:
• Basic nature: Due to the presence of a lone pair of electrons on nitrogen.
• Boiling point: Increases with molecular weight.
• Solubility: Soluble in water (primary and secondary amines) due to hydrogen bonding.
• Basicity: Factors affecting basicity:
  • Inductive effect: Alkyl groups increase basicity by electron donation, while electronegative groups decrease basicity.
  • Steric hindrance: Bulky alkyl groups hinder the protonation of nitrogen, decreasing basicity.
• Reactions:
  • Nucleophilic substitution: R-NH2 + R’-X → R-NHR’ + X-
  • Acylation: R-NH2 + R’-C=O → R-NH-C=O-R'
  • Nitrosation: R-NH2 + NaNO2 + HCl → R-N=O + NaCl + 2 H2O
  • Diazotization: R-NH2 + NaNO2 + HCl → R-N2+Cl- + NaCl + 2 H2O

2. Amides:

• Nomenclature: RCONH2 (primary), RCONHR (secondary), RCONR2 (tertiary).
• Classification: Primary, secondary, tertiary.
• Preparation:
  • From carboxylic acids: RCOOH + NH3 → RCONH2 + H2O
  • From ammonia: RCOOH + 2 NH3 → RCONH2 + NH4+OH-
  • From acid chlorides: R-C=O-Cl + NH3 → R-C=O-NH2 + HCl
• Physical and chemical properties:
• Amide linkage: C=O and N-H bonds are arranged in a planar configuration due to resonance.
• Resonance: Delocalization of electrons between the C=O and N-H bonds.
• Hydrogen bonding: Amides can form hydrogen bonds with water molecules.
• Boiling point: Higher than amines and carboxylic acids due to stronger hydrogen bonding.
• Basicity: Factors affecting basicity:
• Inductive effect: Alkyl groups increase basicity by electron donation, while electronegative groups decrease basicity.
• Steric hindrance: Bulky alkyl groups hinder the protonation of nitrogen, decreasing basicity.
• Reactions:
• Nucleophilic substitution: RCONH2 + R’-X → RCONHR’ + X-
• Hydrolysis: RCONH2 + H2O → RCOOH + NH3
• Reduction: RCONH2 + 4 [H] → RCH2NH2 + H2O

3. Cyanides:

• Nomenclature: R-CN (alkyl cyanides), Ar-CN (aryl cyanides).
• Classification: Alkyl cyanides, aryl cyanides.
• Preparation:
  • From alkyl halides: R-X + KCN → R-CN + KX
  • From potassium cyanide: R-Br + KCN → R-CN + KBr
  • From cyanohydrins: R-C(OH)(CN)2 → R-CN + H2O
• Physical and chemical properties:
  • Nitrile group: The C≡N bond is polar, with a partial positive charge on the carbon and a partial negative charge on the nitrogen.
  • Boiling point: Lower than corresponding carboxylic acids due to weaker hydrogen bonding.
• Reactions:
  • Nucleophilic substitution: R-CN + H2O → R-CONH2
  • Hydrolysis: R-CN + 2 H2O → R-COOH + NH3
  • Reduction: R-CN + 4 [H] → R-CH2NH2
  • Addition of Grignard reagents: R-CN + RMgX → R-C(R’)=NMgX

4. Nitro Compounds:

• Nomenclature: R-NO2 (aliphatic nitro compounds), Ar-NO2 (aromatic nitro compounds).
• Classification: Aliphatic nitro compounds, aromatic nitro compounds.
• Preparation:
  • From alkyl halides: R-X + AgNO2 → R-NO2 + AgX
  • From silver nitrite: R-X + AgNO2 → R-NO2 + AgX
  • From nitric acid: R-H + HNO3 → R-NO2 + H2O
• Physical and chemical properties:
  • Nitro group: The N-O bonds are polar, with a partial positive charge on nitrogen and partial negative charges on oxygen atoms.
  • Resonance: Delocalization of electrons between the N-O bonds.
  • Boiling point: Higher than corresponding hydrocarbons due to stronger dipole-dipole interactions.
• Reactions:
  • Nucleophilic substitution: R-NO2 + H2O → R-OH + HNO2
  • Reduction: R-NO2 + 6 [H] → R-NH2 + 2 H2O
  • Oxidation: R-NO2 + [O] → R-NO3

5. Nitriles:

• Nomenclature: R-C≡N (alkyl nitriles), Ar-C≡N (aryl nitriles).
• Classification: Alkyl nitriles, aryl nitriles.
• Preparation:
  • From alkyl halides: R-X + KCN → R-CN + KX
  • From potassium cyanide: R-Br + KCN → R-CN + KBr
• From dehydration of amides: RCONH2 → RCN + H2O
• Physical and chemical properties:
  • Cyano group: The C≡N bond is polar, with a partial positive charge on the carbon and a partial negative charge on the nitrogen.
  • Boiling point: Lower than corresponding carboxylic acids due to weaker hydrogen bonding.
• Reactions:
  • Nucleophilic substitution: R-CN + H2O → R-CONH2
  • Hydrolysis: R-CN + 2 H2O → R-COOH + NH3
  • Reduction: R-CN + 4 [H] → R-CH2NH2
  • Addition of Grignard reagents: R-CN + RMgX → R-C(R’)=NMgX