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Px Iya thereat A deat! UVon-ferminal alkyne), , 4.7. HOMOLOGOUS SERIES, , We have discussed above that the chemical properties of an organic compound depend upon the, functional group it contains. Thus, all the organic compounds having the same functional group have, similar properties. For example, the chemical properties of CH,OH (methanol), C,H,OH (ethanol), C,H,OH, (propanol), C,H ,OH (butanol) are similar because they have the same functional group (i.e., —OH group)., Therefore, to simply the study of organic chemistry, all the organic compounds having the same functional, group have been arranged in order of their increasing molecular masses and placed in the same family of, organic compounds called a homologous series. Thus,, , A homologous series may be defined as a family of organic compounds having the same, __ functional group, similar chemical properties and the successive (adjacent) members of which —, differ by a CH, unit or 14 mass units., , , , The individual members of a homologous series are called homologues and the phenomenon is called, homology., , 4.7.1. Characteristics of Homologous Series, , 1. All the members of a homologous series can be represented by a general formula. For example, the, , general formula of the homologous series of alkanes is C,H,,,, where ‘n’ is any integer. The molecular, formulae and structures of first six members of this homologous series are given in table 4.2. The molecular, , formula of these six alkanes can be derived as follows :, , (i) If we put n = 1, in the general formula, C,, H>,,, we get C)H>,.1,. = CH, which is the molecular, formula of the first member of the homologous series of alkanes and is called methane., , (ii) If we now put n = 2, in the general formula, C,, H,,,,. we get C>H,»,. = C,H¢ which is the, molecular formula of the second member of the homologous series of alkanes and is called ethane., , In this way, we can derive the molecular formulae of the third, fourth and higher members of this, , homologous series.