Chapter 22.3, Problem 16SSC

Interpretation Introduction

Interpretation:

The general formula for an aldehyde, ketone and a carboxylic acid needs to be determined.

Concept introduction:

The functional group is the group present on the main carbon chain of an organic compound. It determines the chemical properties and the type of reactions an organic compound can show. The name of the group depends on the atoms present in the group for example an −OH group contains O and H atom thus, it is a hydroxyl group. The different functional groups are named according to IUPAC rule.

Name of some functional groups are: -OH: alcohol, -CHO: aldehyde, -COOH: carboxylic acid etc.

Answer to Problem 16SSC

General formula:

Aldehyde: ${\text{C}}_{\text{n}}{\text{H}}_{\text{2n+1}}\text{CHO}$

Ketone: ${\text{C}}_{\text{n}}{\text{H}}_{\text{2n}}\text{O}$

Carboxylic acid: ${\text{C}}_n{\text{H}}_{2n+1}\text{COOH}$

Explanation of Solution

The given organic compounds are aldehyde, ketone and carboxylic acid.

The functional group present in aldehyde, ketone and carboxylic acid is −CHO, -CO- and −COOH respectively.

The general formula of these compounds can be determined by taking the simplest molecules containing these functional groups.

For aldehyde, the simplest molecule is formaldehyde which is HCHO and ethanal which is CH₃CHO. From these molecules, it can be seen that -CHO group is common. Let the number iof carbon atoms excluding the C atom in CHO be n thus, the number of H atoms will be 2n+1.

This makes the general formula of aldehyde to be ${\text{C}}_{\text{n}}{\text{H}}_{\text{2n+1}}\text{CHO}$.

For ketone, the simplest molecule is propanone which is CH₃COCH₃. Let the number of carbon atoms be n thus, the number of H atoms will be 2n and there is only 1 O atom in all the ketone molecules.

Thus, the general formula of ketone will be ${\text{C}}_{\text{n}}{\text{H}}_{\text{2n}}\text{O}$.

For carboxylic acid, the simplest molecule is formic acid which is HCOOH and ethanoic acid which is CH₃COOH. From these molecules, it can be seen that -COOH group is common. Let the number of carbon atoms excluding the C atom in COOH to be n thus, the number of H atoms will be 2n+1.

This makes the general formula of carboxylic acid to be ${\text{C}}_{\text{n}}{\text{H}}_{\text{2n+1}}\text{COOH}$.

Conclusion

Thus,

General formula:

Aldehyde: ${\text{C}}_{\text{n}}{\text{H}}_{\text{2n+1}}\text{CHO}$

Ketone: ${\text{C}}_{\text{n}}{\text{H}}_{\text{2n}}\text{O}$

Carboxylic acid: ${\text{C}}_n{\text{H}}_{2n+1}\text{COOH}$