5.5.1 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

Amine Classification, downloadable AS & A Level Chemistry revision notes

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

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 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

general-amide-structure

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

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

The R group varies in different amino acids and can be:
- Acidic
- Basic
- Neutral

Nitrogen Compounds - Different Types of Amino Acids, downloadable AS & A Level Chemistry revision notes

The R group varies in different amino acids

Edexcel International A Level Chemistry

5.5.1 Amines, Amides & Amino Acids - Introduction