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What is homologous series explain with an example?

A homologous series is a group of organic compounds that have the same general formula and similar chemical properties because they have the same functional group and differ by a constant unit. They also show a gradual increase or decrease in their physical properties such as boiling point, melting point, density, and solubility as the number of carbon atoms increases or decreases.

For example, the homologous series of alkanes has the general formula CnH2n+2, where “n” represents the number of carbon atoms. The first member of this series is methane (CH4), which has only one carbon atom, followed by ethane (C2H6), propane (C3H8), butane (C4H10), pentane (C5H12), and so on. As the number of carbon atoms increases, the physical properties such as boiling point, melting point, and density increase gradually.

Similarly, the homologous series of alcohols has the general formula CnH2n+1OH, where “n” represents the number of carbon atoms. The first member of this series is methanol (CH3OH), followed by ethanol (C2H5OH), propanol (C3H7OH), butanol (C4H9OH), pentanol (C5H11OH), and so on. As the number of carbon atoms increases, the physical properties such as boiling point, melting point, and density also increase gradually.

Homologous series are essential in organic chemistry as they help in predicting the properties of new compounds and in understanding the relationship between structure and function of organic molecules.