6.2.2 - amino acids, amides, chirality

• The two functional groups of amino acids are NH2 and COOH ( amine and carboxyl )
• A-amino acids are when the the amine and carboxyl group are bonded to the same carbon.
• a-amino acids are chiral because one carbon has 4 different substituents.
• the only a-amino acid that is not chiral is glycine where R = H
• A zwitterion are ions which have both a permanent positive and negative charge but are neutral overall
• zwitterions occur in amino acids when COOH is deprotonated —> COO- and when NH2 is protonated ——> NH3+
• in acidic conditions, amino acids gain a proton on the NH2 group
• In alkaline conditions, amino acids lose a proton from the COOH group
• The peptide linkage is -CONH-
• Primary amides have an Acyl group bonded to a nitrogen atom that is bonded to 2 Hydrogens
• secondary amides have an Acyl group bonded to a nitrogen atom that is bonded to 1 hydrogen atom
• To display optical isomerism, a carbon must have 4 different substituents attached to one carbon atom
• similarities and differences between two optical isomers include:

  Same atoms and bonds, but they are non-superimposable mirror images of one another.

  Differ in the way they rotate and how plane is polarised by light.
• Chiral molecules are ones with four different groups attached to them
• Optically active molecules are chiral
• two optical isomers of one another are known as enantiomers
• to draw two optical isomers draw the 3D displayed formula of the molecule and then draw the mirror image