Amides (OCR A Level Chemistry)

• Amides are formed from the condensation reaction of carboxylic acids or acyl chlorides with ammonia or amines
• Amides are common in nature such as in proteins where the amine and carboxylic acid groups of amino acids bond together
• Amides have a general structure of RCONR₂

The general structure of an amide

• Amides can be classified as primary, secondary or tertiary amides
• Like amines, this is done as a comparison to ammonia, depending on the number of substitutions on the amide nitrogen 
  • Primary amide - one carbon bonded to the amide nitrogen 
    • R' and R'' are both hydrogen atoms so one "ammonia" hydrogen has been substituted with the carbonyl group from the RCO portion of the molecule
  • Secondary amide - two carbons bonded to the amide nitrogen (one MUST be the carbonyl carbon)
  • Tertiary amide - three carbons bonded to the amide nitrogen (one MUST be the carbonyl carbon)

Naming primary amides

• For primary amides, we simply add -amide to the stem name
  • e.g. CH₃CONH₂
    • Contains two carbons with a C-C (ethan-) and an amide group (-amide)
    • This gives us ethanamide

Naming secondary amides

• For secondary amides, the alkyl chain attached to the nitrogen is added at the start of the chemical name
• This alkyl chain is prefixed with N-
• The chain containing the carbonyl group is named the same as a primary amide
  • e.g. CH₃CONH(C₃H₇)
    • Contains a propyl group on the nitrogen (N-propyl) 
    • Contains two carbons with a C-C (ethan-) and an amide group (-amide)
    • This gives us N-propylethanamide

Naming tertiary amides

• For tertiary amides, there are two alkyl chains attached to the nitrogen
• The naming of these chains is the same as secondary amides
• As with standard nomenclature, these chains are listed in alphabetical order and the prefix 'di-' is used if necessary
  • e.g. CH₃CONCH₃(C₃H₇)
    • Contains a methyl group on the nitrogen (N-methyl)
    • Contains a propyl group on the nitrogen (N-propyl) 
    • Contains two carbons with a C-C (ethan-) and an amide group (-amide)
    • This gives us N-methyl-N-propylethanamide