Alcohol
Alcohols can be define as a compounds in which a hydrogen of an alkane has been replaced by an -OH group. They have –OH group (a hydroxyl) bonded to a saturated alkane like carbon atom R- OH where R is any simple alkyl or substituted alkyl group.
For example:
CH3OH CH3CH2OH
methanol ethanol
CH3-CH-CH2OH
|
CH3
2-methyl propan-1-ol
Classification of Alcohols
Alcohols can have one or more hydroxyl group composition, these composition are further subjected to sub categorization. the categorization are assigned base on the number of -OH attached to the alkyl group. the categorization include:
- Monohydric – contain only one hydroxyl group. For example, ethanol.
CH3-CH2-CH2-OH
Ethanol
- Dihydric- contain two hydroxyl groups. For example ethane-1,2-diol.
CH2 – CH2
| |
OH OH
- Trihydric- contains three hydroxyl groups. For example, propane-1, 2, 3-triol.
Generally with more than one hydroxyl group, it is said to be polyhydric.
Monohydric alcohols have the general formula CnH2n + 1OH. They can be classified into three classes – primary (1o), secondary (2o) and tertiary alcohol (3o) according to the number of alkyl groups attached to the hydroxyl-bonded carbon atom.
(i) Primary alcohol (l°)
It has one alkyl group attached to the hydroxyl bonded carbon atom.
H
|
R — C—OH
|
H
For example, CH3OH CH3CH2OH Methanol Ethanol
CH3 H
| |
CH3—C— C—OH
| |
CH3 H
2,2-dimethylpropan-1-ol
Secondary alcohol (2o):
There are two alkyl groups attached to the hydroxyl-bonded carbon atom.
R’
|
R—C—OH
|
H
| For example:
|
CH2CH3 | CH3—C—OH | H Butan-2-ol |
|
|
CH3 | CH3—C—OH | H Propan-2-ol |
Tertiary (3o):
There are three alkyl groups, but no hydrogen atom directly attached to the hydroxyl-bonded carbon atom.
R’
|
R—C—OH
|
R”
For example:
CH3
|
CH3 —C—OH
|
CH3
2—methyl propan—2—ol
CH2CH3
|
CH3CH2—C—OH
|
CH3
3—methylpentan—3—ol
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