Amines, Amides, Amino Acids & Proteins

Amines are organic derivatives of ammonia ($NH_3$) where one or more hydrogen atoms are replaced by alkyl or aryl groups, retaining a lone pair of electrons on the nitrogen atom.

Classification of amines is determined by the number of carbon groups attached directly to the nitrogen: primary ($RNH_2$), secondary ($R_2NH$), and tertiary ($R_3N$).

Amides contain the $-CONR_2$ functional group, characterized by a carbonyl group ($C=O$) directly bonded to a nitrogen atom, which significantly alters the chemical properties compared to amines.

Amino Acids are bifunctional molecules containing both a basic amino group ($-NH_2$) and an acidic carboxylic acid group ($-COOH$), typically bonded to the same central alpha-carbon.

Preparation of Primary Amines: These can be synthesized via the nucleophilic substitution of halogenoalkanes with excess ethanolic ammonia or by the reduction of nitriles using $LiAlH_4$ in dry ether.

Aromatic Amine Formation: Nitrobenzene is reduced to phenylamine in a two-stage process: first heating with Tin ($Sn$) and concentrated $HCl$ under reflux, followed by the addition of excess $NaOH$ to liberate the free amine.

Amide Synthesis: Amides are formed through a condensation reaction between an acyl chloride and ammonia (for primary amides) or an amine (for substituted amides), eliminating $HCl$ in the process.

Condensation Polymerization: Polyamides like Nylon 6,6 are produced by reacting dicarboxylic acids with diamines, where each monomer has two functional groups, allowing for the formation of long repeating chains.

Aliphatic vs. Aromatic Amines: Aliphatic amines are more basic than ammonia due to inductive effects, whereas aromatic amines are less basic due to resonance stabilization of the lone pair.

Addition-Elimination vs. Substitution: The reaction of amines with acyl chlorides is an addition-elimination mechanism, whereas their reaction with halogenoalkanes is nucleophilic substitution.

Identify Monomers: When given a polymer structure, look for the amide link ($-CONH-$). Break the bond between the $C=O$ and the $N$ to identify the original dicarboxylic acid and diamine components.

Zwitterion Drawing: Always check the pH specified in the question. At low pH, ensure the amino group is protonated ($-NH_3^+$); at high pH, ensure the carboxyl group is deprotonated ($-COO^-$).

Basicity Explanations: When comparing basicity, always mention the 'availability of the lone pair' and explain it using either the 'positive inductive effect' or 'delocalization into the ring'.

Naming Nuances: For secondary and tertiary amides, remember to use the '$N$-' prefix (e.g., $N$-methylethanamide) to indicate substituents attached directly to the nitrogen atom.