Amino Acids

Quick Notes

• α-Amino Acids have the general structure:

• RCH(NH₂)COOH
• The COOH group gives acidic properties and the NH₂ group gives basic properties.
• Common Reactions:
  • Can react with alkalis to form a carboxylate salt.
  • Can react with acids to form an ammonium salt.
  • Can react with alcohols to form esters (acid catalyst needed).

Full Notes

Structure of α-amino acids

α-Amino acids have the general formula:

H₂N–CHR–COOH (where R is a side chain).

The amine (–NH₂) group acts as a base and the carboxylic acid (–COOH) group acts as an acid.

Reactions of α-amino acids

You need to know the following reactions of amino acids.

With alkalis (bases)

The carboxylic acid group reacts with a base and loses a H⁺ ion, forming a carboxylate salt.

Example Reaction with NaOH

H₂NCH(R)COOH + NaOH → H₂NCH(R)COO⁻Na⁺ + H₂O

With acids

The amine group acts as a base and accepts a H⁺ ion from the acid, forming an ammonium salt:

Example Reaction with HCl

H₂NCH(R)COOH + HCl → H₃N⁺CH(R)COOH Cl⁻

Esterification (with alcohols and acid catalyst)

The COOH group can form esters:

Example Reaction with an alcohol

H₂NCH(R)COOH + ROH ⇌ H₂NCH(R)COOR + H₂O

Requires an acid catalyst (e.g. H₂SO₄).

Summary

• α-Amino acids have the general formula H₂N–CHR–COOH with both acidic and basic functional groups.
• The COOH group reacts with alkalis to form carboxylate salts.
• The NH₂ group reacts with acids to form ammonium salts.
• The COOH group reacts with alcohols in the presence of acid catalysts to form esters.