ORGANIC COMPOUNDS WHICH ARE DERIVED BY REPLACING ONE OR MORE HYDROGRN ATOMFROM THE ALPHATIC HYDROCARBON BY THE SAM NUMBER OF HYDROXYL GROUPS ARE ALIPHATIC ALCOHOLS.
Depending on the types of hydrocarbons, they are of two types: aliphatic and aromatic alcohols.
a. Alcohols have been classified as following on the basis of number of OH group:
i)Monohydric alcohols: It contains only one –OH group.
ii)Dihydric alcohols: It contains two –OH groups.
iii)Trihydric alcohols: It contains three –OH groups.
iv)Polyhydric Alcohols: It contains more than three –OH groups.
b. Alcohols have been classified into three types depending on the no. of C-atoms directly attached to the carbon containing –OH group;
i)Primary alcohols: In this alcohol, Carbon containing –OH group is directly attached to only one carbon or none.
ii)Secondary alcohols: Carbon containing –OH group is directly attached to two carbon atoms.
iii)Tertiary alcohols: Carbon containing –OH group is directly attached to three carbon atoms.
1.Common System
In this system, monohydric alcohols are named as alkyl alcohol. The –ane of alkane is replaced by –yl and word alcohol is added. Also, if three or more than 3 C-atoms are present, then prefix n-, iso-, sec-, tert- , and neo- are added.
2.IUPAC Nomenclature for Alcohols
•The following procedure should be followed in giving alcohol IUPAC substitutive names.
•Select the longest continuous chain to which the hydroxyl group is directly attached. Change the name of the alkane corresponding to the chain by replacing the final -e with the suffix -ol.
•Number the longest continuous carbon chain so as to give the carbon atom bearing the hydroxyl group the lower number.
•Indicate the position of another substituent as a prefix by using the numbers corresponding to their positions along the carbon chain as locants.
If more than one –OH group is present, then suffixes –diol,-triol etc. are used and “e” ending of parent alkane is retained.
Alcohols shows the following types of structural isomerism :
i)Chain Isomerism: Alcohols having same molecular formula, but different carbon skeleton give rise to chain isomerism. Eg: C4H9OH or C4H10O
i)Positional isomerism: Alcohols having same molecular formula but different in the position of –OH group in the identical carbon chain give rise to Positional isomerism. Eg: C3H7OH or C3H8O
iii) Functional isomerism: Alcohols having same molecular formula but different in functional group gives rise to functional isomerism. Eg: C2H5OH or C2H6O
Alcohols shows functional isomerism with ethers. Alcohols and ethers are functional isomers of each other as both of them have same general molecular formula as CnH2n+2O.
