Amines are functional groups and compounds having a basic nitrogen atom with a lone pair. In other terms they are the derivatives of ammonia(NH3). wherein for instance one or more hydrogen atoms will replace a substituent like the alkyl and aryl. These are respectively alkyl amines and aryl amines.
However, they occur when all the substituted forms like the aryl and alkyl are attached to one nitrogen is known as as alkyl aryl amines. Structurally, these compounds resemble ammonia therefore the nitrogen can be in bond upto 3 hydrogen atoms
In addition in Nitrogen the presence of 5 valence electrons results in a trivalent with a lone pair. As per VSEPR theory, nitrogen present in them is therefore sp3 hybrid.
however due to the presence of lone pair, nitrogen is pyramidal in shape instead of tetrahedral shape .
For instance ,the general structure for most sp3 hybridized molecules are however tetrahedral in shape .
Each of the three sp3 hybridized orbitals of nitrogen overlap with orbitals of hydrogen or carbon depending upon the configuration.The presence of the lone pair, makes the C-N-H angle in amines less than 109 degrees, however this is characteristic angle of tetrahedral geometry. The angle is near about 107 degrees.
Types of Amines
They can be classified into four types on the basis of how ammonia molecule replace the hydrogen atoms
- Primary Amines
If one of the hydrogen atoms in an ammonia molecule shows substitution by an alkyl or aryl group, it is a primary amine
- Secondary Amines
Two organic substituents are useful to remove the hydrogen atom in the ammonia molecule,that forms an amine
Examples: Diphenylamine, Dimethylamine
- Tertiary amines
Tertiary occurs when all the three hydrogen atoms are substituted with an organic substitution, therefore forming an aryl or aromatic group.
Example: EDTA( ethylenediaminetetraacetic acid), Trimethylamine
- Cyclic Amines
they are compounds where the nitrogen has been blend into a ring structure by forming either a secondary or tertiary amine effectively
For instance: A three membered ring azidirine, a six membered ring piperidine.
Similar to ammonia , the primary and secondary amines possess protic hydrogens and therefore show a degree of acidity .
However the tertiary amines do not have protein hydrogen and therefore do not have a degree of acidity.
The pKa value for both primary and secondary is around 38, therefore they form a very weak acid.