Amines, Amides & Amino Acids - Introduction (Edexcel International A Level Chemistry): Revision Note

Amines, Amides & Amino Acids - Introduction

• Amines can be thought of as derivates of ammonia, in which one or more of the hydrogens is replaced by an alkyl or aryl group

• The number of substituted hydrogens is the basis of classifying amines

Classification of amines

• Notice the classification is not the same as in alcohols and haloalkanes, where the designation primary, secondary and tertiary is based on the substituents on the carbon atom rather than the nitrogen atom

• If the R group is an alkyl group (methyl, ethyl, etc) then then it is an aliphatic amine; if it is an aryl group (benzene ring or phenyl) then it is an aromatic amine

• Aliphatic and aromatic amines share similar chemical reactions and the aryl group can strongly influence the chemistry and reactivity of the amine group

Naming Amines

• Amines can be named using common names or IUPAC systematic names

• The common way to name amines is to use the alkyl (or aryl) prefix followed by -amine

• The IUPAC systematic name uses the numbered prefix amino- followed by the alkane (or aromatic) stem

Nomenclature of Aliphatic and Aromatic Amines Table

Amides

• 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

Amino acids

• Amino acids are organic compounds that contain two functional groups:

  • A basic amino (-NH₂) group

  • An acidic carboxylic acid (-COOH) group

• Due to the presence of both a basic and acidic group in amino acids, they are said to be amphoteric

  • They can act as both acids and bases

Naturally occurring amino acids

• 2-aminocarboxylic acids are a type of amino acids in which the amine (-NH₂) group is bonded to the carbon atom next to the -COOH group

• These type of amino acids form the ‘building blocks’ that make up proteins

• There are 20 naturally occurring amino acids with the general structural formula of RCH(NH2)COOH

General structural formula of amino acids

General structural formula of amino acids

• The R group varies in different amino acids and can be:

  • Acidic

  • Basic

  • Neutral

The R group varies in different amino acids