Ethane CH CH Propane CH CH CH Butane CH (CH ) CH Pentane CH (CH ) CH If you observe the above series. you can notice that each successive member has one methylene group more than the precedent member of the series and hence they are called homologs. . .
Characteristics of homologous series Each member of the series differs from the preceding or succeeding member by one methylene group (–CH ) and hence by a molecular mass of amu. All members of a homologous series contain the same elements and functional group. They are represented by a general molecular formula. e.g.
Alkanes, C n H 2n + . The members in each homologous series show a regular gradation in their physical properties with respect to their increase in molecular mass. Chemical properties of the members of a homologous series are similar. All the members can be prepared by a common method.
Table . Classes of organic compounds based on functional group Class of the compound Functional group Common Formula Examples Alcohol –OH R -OH Ethanol, CH CH OH Aldehyde O || −C−H R -CHO Acetaldehyde, CH CHO Ketone O || −C− R –CO- R Acetone, CH CO CH Carboxylic acid O || −C−OH R -COOH Acetic acid, CH COOH Ester O || −C−OR R -COOR Methyl acetate, CH COOCH Ether –O–R R -O-R Dimethyl ether, CH OCH . NOMENCLATURE OF ORGANIC COMPOUNDS . .
Why do we need nomenclature? In ancient days, the names of organic compounds were related to the natural things from which they were obtained. For example, the formic acid was initially obtained by distillation of ‘red ants’. Latin name of the red ant is ‘Formica’.
So, the name of the formic acid was derived from the Latin name of its source Later, the organic compounds were synthesized from sources other than the natural sources. So scientists framed a systematic method for naming the organic compounds