Concise Notes on Nitrogen Compounds: Amines, Amides, Amino Acids, and Proteins

Amines

• Derivatives of ammonia ($NH_3$), classified as primary, secondary, or tertiary based on the number of alkyl or aryl groups attached to the nitrogen atom.
• Amines can also be classified into aliphatic and aromatic amines depending on the group attached to the Nitrogen atom.
• Named by specifying alkyl groups attached to the nitrogen atom, with the largest alkyl group as the parent name.
• Volatility decreases with increasing carbon number due to stronger London dispersion forces.
• Amines have higher boiling points than non-polar compounds due to hydrogen bonding (except tertiary amines).
• Amines have lower boiling points than alcohols because N-H bonds are less polar than O-H bonds.
• Aliphatic amines are water-soluble due to hydrogen bond formation; solubility decreases with carbon number.
• Amines are weak Lewis bases; basicity depends on the availability of the lone pair of electrons on the nitrogen atom.
• In the gaseous phase, basicity increases with the number of methyl groups attached to N.
• Ethylamine is more basic than ammonia; phenylamine is less basic due to delocalization of the lone pair into the benzene ring.
• Amines react with acids to form salts.
• Amines act as nucleophiles, reacting with acid chlorides to form amides and with halogenoalkanes in nucleophilic substitution.
• Aromatic amines undergo electrophilic substitution with aqueous bromine.
• Amines can be formed through Nucleophilic substitution of halogenoalkanes with $NH_3$ or amines, Reduction of nitriles, Reduction of amides, Reduction of nitrobenzene

Amides

• Amides are classified as primary, secondary, or tertiary based on alkyl/aryl groups bonded to the nitrogen atom.
• Amides have high melting points due to intermolecular hydrogen bonding.
• Solubility in water decreases with increasing molecular mass.
• Amides are neutral and do not function as bases or nucleophiles due to the delocalization of the lone pair of electrons on the nitrogen atom into the electron system of C=O.
• Amides are prepared by reacting an acyl chloride with ammonia or an amine.
• Amides undergo hydrolysis in acidic (forms carboxylic acid and ammonium salt) or alkaline conditions (forms salt of carboxylic acid and ammonia).
• Amides can be reduced to amines using $LiAlH_4$.
• Primary amides can be identified by heating with NaOH(aq), which releases $NH_3$ gas that turns moist red litmus paper blue.

Amino Acids

• Contain a basic amine group, an acidic carboxylic acid group, and an R group.
• Exist as zwitterions in solid phase or aqueous solutions.
• Have high melting points and are soluble in water due to their dipolar nature.
• Act as amphoteric compounds, reacting with both acids and bases.
• Can act as buffers by resisting pH changes.
• Amino acids polymerize through peptide (amide) bonds, forming dipeptides, tripeptides, polypeptides, and proteins.

Proteins

• Polymers of amino acids with various functions.
• Formed by condensation polymerization.
• Hydrolyzed into constituent amino acids by heating with NaOH or sulfuric acid, or using specific enzymes.
• Partial hydrolysis produces fragments that help determine the amino acid sequence.