Download Aromatic amines The

Amines
A Nitrogen, containing a lone pair is the key atom
Resembles Ammonia where one or more H’s
Are replaced by alkyl groups
The lone pair participates in the reactivity
Of amines
Amines are a core part of ‘amino acids’
Amines (structure)
A fourth group is attached to the nitrogen atom
Using the lone pair. This is known as a
quaternary Ammonium ion
2-aminoethanol
2-aminopentane
TRIS buffer, used widely in
biochemistry
Other examples:
2-dimethylaminoethanol
2-methylaminoethanol
Amine Nomenclature (contd)
Aromatic amines
►The –NH2 functional group is an amino group, and when this group
is a substituent, amino- is used as a prefix
►The presence of the amine group increases the reactivity of the
aromatic ring
Properties of amines: Basicity
•Amines are electron pair donors
•Bronsted-Lowry bases or lewis bases
Difference of boiling pts., similar molecular weights, why ?
-H-bonding significantly affects b.p
-Amine b.p are generally lower than alcohols
-Soluble in water (upto 6 carbons)
-Gaseous amines smell like ammonia, liquid amines have a
A characteristic ‘fishy’ smell!!
Will 3o amines have higher b.p than 1o amines ?
Heterocyclic Nitrogen compounds
Heterocycles are common in many naturally derived products
Back to basicity of Amines
Basicity depends on:
- Availability of Lone pair of electrons
- Is the protonated form of the amine water-soluble?
- Substituent groups on the amine
Ions of compound
Kb
Ammonia NH3
1.8·10-5 M
Methylamine CH3NH2
4.4·10-4 M
propylamine CH3CH2CH2NH2
4.7·10-4 M
2-propylamine (CH3)2CHNH2
5.3·10-4 M
diethylamine (CH3)2NH
9.6·10-4 M
Quarternary ions
Note: heterocyclic ammonium ions are named by using –ium instead of -e