Question

What is the formula of 4-methyl butanoic acid?

Answer 1

According to IUPAC nomenclature of the organic compound the function group butanoic acid represents that the given compound must contain a carboxyl group. The name of the acid represents the number of carbon atoms present in the carbon chain including the carbon atom of carboxylic acid. The name of the substituent is represented at the beginning of the IUPAC name of the compound.

Complete answer:
In the given compound, 4-methyl butanoic acid , according to IUPAC nomenclature, the suffix butanoic acid represents the presence of a carboxylic acid group in the structure of the compound. Also Butanoic acid represents the number of carbon atoms present in it including carbon atoms of the carboxylic acid group. Therefore we can say that the number of carbon atoms exempting the carboxylic acid is three. Therefore we can draw its structure as:
$C{H_3} - C{H_2} - C{H_2} - COOH$
Now the prefix represents that a methyl group is present at the fourth carbon atom in the above structure. Therefore we have to give number to carbon atoms according to IUPAC rule which can be shown as:
${}^4C{H_3} - {}^3C{H_2} - {}^2C{H_2} - {}^1COOH$
Therefore we will attach a methyl group at fourth carbon atom as:
$C{H_3} - {}^4C{H_3} - {}^3C{H_2} - {}^2C{H_2} - {}^1COOH$
Thus we observe that 4-methyl butanoic acid is none other but pentanoic acid. Therefore the correct IUPAC name of 4-methyl butanoic acid is pentanoic acid. Its molecular formula will be ${C_5}{H_{10}}{O_2}$.

Note:
We have written the structural formula and molecular formula of 4-methyl butanoic acid. Its bond line formula can also be written while representing all the bonds including carbon-hydrogen bonds. The numbering of carbon atoms must be according to IUPAC rule.