Question

The general formula for alcohol series is ${C_n}{H_{2n + 1}}OH$. Which formula for alcohol contains four carbons?
A. ${C_5}{H_{11}}OH$
B. ${C_4}{H_9}OH$
C. ${C_4}{H_8}OH$
D. ${C_3}{H_8}OH$

Answer 1

Hint: Alcohols are the compounds containing hydroxyl groups ($ - OH$) as a functional group in them. An alcohol is formed by replacing a hydrogen atom in an alkane with a hydroxyl group. The general formula of an alcohol is given as ${C_n}{H_{2n + 1}}OH$. So when the no. of carbons is 1 in an alcohol, then the no. of hydrogens will be $2\left( 1 \right) + 1 = 3$. In this way we are finding the no. of hydrogens present in an alcohol with four carbon atoms excluding the hydrogen in hydroxyl group.

Complete step by step solution:
We are given the general formula for alcohol series is ${C_n}{H_{2n + 1}}OH$.
We have to find the formula for alcohol with four carbons.
As we can see in the first option ${C_5}{H_{11}}OH$, the alcohol contains five carbon atoms. So it is not our required answer.
And the fourth option is ${C_3}{H_8}OH$, it contains three carbon atoms. Therefore it is not our answer.
Third option ${C_4}{H_8}OH$ has four carbon atoms, but the no. of hydrogen atoms is 8. When an alcohol has 4 carbon atoms, then it should have $2\left( 4 \right) + 1 = 9$ hydrogen atoms excluding the hydrogen of hydroxyl group. Here it is 8 not 9, so this alcohol is not our required answer.
Second option is ${C_4}{H_9}OH$, here the no. of carbon atoms is 4 and the no. of hydrogen atoms is 9. It satisfy the general form of an alcohol as ${C_n}{H_{2n + 1}}OH = {C_4}{H_{2\left( 4 \right) + 1}}OH = {C_4}{H_9}OH$
${C_4}{H_9}OH$ is called 1-butanol or butyl alcohol.

Therefore, the correct option is Option B.

Note:
In chemistry, organic compounds which have a general formula are Alkanes, alkenes, alkynes, alcohols, ethers, aldehydes, ketones, acids and esters. The general formula of alcohol and ether are the same. If these both compounds contain the same number of carbon atoms, then the corresponding no. of hydrogen atoms and oxygen atoms are also the same. So be careful with alcohol and ether.