Alcohol and alcohol classification

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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Alcohols can be define as a compounds in which a hydrogen of an alkane has been replaced by an -OH group.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:

  1. Monohydric          – contain only one hydroxyl group. For example, ethanol.

 

CH3-CH2-CH2-OH

Ethanol

 

  1. Dihydric- contain two hydroxyl groups. For example ethane-1,2-diol.

 

CH2  – CH2

|          |

READ ALSO  Spectral line of Atom

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

|

CH—C—OH

|

CH3

2—methyl propan—2—ol

CH2CH3

|

CH3CH2—C—OH

|

CH3

3—methylpentan—3—ol

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