Amines, Amides and Amino Acids

Methods for preparation of aliphatic amines

Substitution with haloalkanes or reduction of nitriles

Method for preparation of aromatic amines

Reduction of nitrobenzene

Base strength of amines

Dependent on ability of lone pair on N to be donated/accept H⁺ - therefore tertiary amine strongest base and aromatic amine weakest

Haloalkane substitution product (XS NH₃)

Primary amine

Haloalkane substitution product (XS haloalkane)

Quaternary ammonium salt

Quaternary ammonium salt surfactant structure

Hydrophilic ionic head and hydrophobic alkyl-chain tail

Micelle formation

Surfactant molecules surround dirt/grease → hydrophobic tail dissolves grease and hydrophilic head dissolves in water

Products of acylation of an amine

Amide + HCl (with acyl chloride) or carboxylic acid (with acid anhydride)

Product of amine reaction with acid

Ammonium salt

Amino acid functional groups

Amine group and carboxylic acid group

Natural form of amino acids

Zwitterions - each amine group is protonated by a carboxylic acid group on another molecule, creating both +ve and -ve charges on molecule

Amino acid standard state

Solid due to ionic interactions between zwitterions

Optical isomerism of amino acids

Except glycine, all amino acids have a chiral C - but only one enantiomer is present in nature

Primary structure of amino acids

Chain - the sequence of amino acid units

Secondary structure of amino acids

Usually a helix held together by H-bonds between C=O and H-N in adjacent spirals

Tertiary structure of amino acids

Overall shape - folding of helix into characteristic 3D shape forms structure held together by electrostatic interactions, H-bonds, and disulfide bridges

Reactions of amine group on amino acids

Protonation by acids, acylation, and nucleophilic substitution with haloalkanes

Reactions of acid group on amino acids

Deprotonation by bases, and esterification

Formation of proteins/peptides

Amino acids join in condensation reactions to form dipeptides or polypeptides - proteins are long-chain polypeptides

Hydrolysis of peptides using strong acid

Amino acid forms with protonated amine group

Hydrolysis of peptides using strong alkali

Amino acid forms with deprotonated carboxylic acid group

Reaction of amino acids with NaOH

Carboxylic acid group deprotonated

Reaction of amino acids with HCl

Amine group protonated

Reaction of amino acids with ethanol and conc. sulphuric acid

Carboxylic acid group forms ester

Acylation of amino acids

Amine group loses H and gains acyl group