Question

Write down structural formulae of the first four members of the various homologous series formed by making use of the functional groups.

Accepted Answer

The alcohol series is a homologous series with the general formula $C_{n} H_{2 n + 1} OH$ , and each member will differ by a $- {CH}_{2} -$ group. The first four members of the alcohol series along with their structures are listed below:

Methanol is the first member of the alcohol series with the formula ${CH}_{3} OH$ , ethanol is the second member of alcohol series with the formula ${CH}_{3} {CH}_{2} OH$ , and propanol is the third member of the alcohol series with the formula ${CH}_{3} {CH}_{2} {CH}_{2} OH$ . And butanol is ${CH}_{3} {CH}_{2} {CH}_{2} {CH}_{2} OH$ . The structural formula of these four compounds are given below:

The aldehyde series is a homologous series with the functional group $- CHO$ . It is a terminal functional group. The first four members of aldehyde series are methanal with the formula $HCHO$ , ethanal with the formula ${CH}_{3} CHO$ , and propanal with the formula ${CH}_{3} {CH}_{2} CHO$ , and butanal with the formula ${CH}_{3} {CH}_{2} {CH}_{2} CHO$ . The structural formula of these four compounds are given below:

The ketone series is a homologous series with the functional group $- CO -$ . It is a non-terminal functional group. The first four members of ketone series are propanone with the formula ${CH}_{3} {COCH}_{3}$ , 2-butanone with the formula ${CH}_{3} {COCH}_{2} {CH}_{3}$ , 2-pentanone with the formula ${CH}_{3} {COCH}_{2} {CH}_{2} {CH}_{3}$ , and 2-hexanone with the formula ${CH}_{3} {COCH}_{2} {CH}_{2} {CH}_{2} {CH}_{3}$ . The structural formula of these four compounds are given below:

The carboxylic acid series is a homologous series with the general formula $C_{n} H_{2 n + 1} COOH$ , and each member will differ by a $- {CH}_{2} -$ group. The first four members of the series along with their structures are listed below:

Methanoic acid is the first member of the series with the formula $HCOOH$ , ethanoic acid is the second member of the series with the formula ${CH}_{3} COOH$ , propanoic acid is the third member with the formula ${CH}_{3} {CH}_{2} COOH$ , and butanoic acid is the fourth memeber with the formula ${CH}_{3} {CH}_{2} {CH}_{2} COOH$ . The structural formula of these four compounds are given below:

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