Chapter 5, Problem 22P

Write structural formulas for all the constitutionally isomeric alcohols of molecular

formula $C_5{H}_{12}O$. Assign a substitutive and a functional class name to each one, and specify whether it is a primary, secondary, or tertiary alcohol.

Interpretation Introduction

Interpretation:

The structural formulas for the constitutionally isomeric alcohols of molecular formula ${\text{C}}_{\text{5}}{\text{H}}_{\text{12}}\text{O}$ are to be written. A substitutive and a functional class name is to be assigned and the type of alcohol is to be specified for each alcohol.

Concept Introduction:

Isomers that have the same molecular formula but differ in the way in which different atoms are connected are known as constitutional isomers.

The number of atoms of each element present in the compound, is known as the molecular formula.

When the functional group $\text{-OH}$ is attached to a primary carbon atom, the alcohol is classified as primary alcohol. Similarly, when the functional group $-\text{OH}$ is attached to a secondary or tertiary carbon atom, the alcohol is classified as secondary or tertiary alcohol respectively.

Answer to Problem 22P

Solution:

There are 8 constitutionally isomeric alcohols of molecular formula ${\text{C}}_{\text{5}}{\text{H}}_{\text{12}}\text{O}$, which can be given as follows.

Substitutive name: $\text{1- pentanol}$ or $\text{pentan-1-ol}$

Functional class name: pentyl alcohol

It is a primary alcohol.

Substitutive name: $\text{2- pentanol}$ or $\text{pentan-2-ol}$

Functional class name: $1-methylbutylalcohol$

It is a secondary alcohol.

Substitutive name: $3-\text{pentanol}$ or $\text{pentan-3-ol}$

Functional class name: $\text{1-ethylpropyl alcohol}$

It is a secondary alcohol.

Substitutive name: $\text{2-methyl-1-butanol}$ or $\text{2-methylbutan-1-ol}$

Functional class name: $2-methylbutylalcohol$

It is a primary alcohol.

Substitutive name: $\text{3-methyl-1-butanol}$ or $\text{3-methylbutan-1-ol}$

Functional class name: $\text{3-methylbutyl alcohol}$

It is a primary alcohol.

Substitutive name: $\text{2-methyl-2-butanol}$ or $\text{2-methylbutan-2-ol}$

Functional class name: $\text{1,1-dimethylpropyl alcohol}$

It is a tertiary alcohol.

Substitutive name: $\text{3-methyl-2-butanol}$ or $\text{3-methylbutan-2-ol}$

Functional class name: $1,2-dimethylpropylalcohol$

It is a secondary alcohol.

Substitutive name: $\text{2,2-dimethyl-1-propanol}$ or $\text{2,2-dimethylpropan-1-ol}$

Functional class name: $2,2-dimethylpropylalcohol$

It is a primary alcohol.

Explanation of Solution

In all, there are $8$ constitutionally isomeric alcohols of molecular formula ${\text{C}}_{\text{5}}{\text{H}}_{\text{12}}\text{O}$.

They have the same molecular formula but different connectivity of atoms.

The structural formulas of these alcohols can be written as follows.

The substitutive name of this alcohol is $\text{1- pentanol or pentan-1-ol}$.

The functional class name of this alcohol is pentyl alcohol.

The hydroxyl group is attached to a primary carbon atom. Hence, it is a primary alcohol.

The substitutive name of this alcohol is $\text{2- pentanol or pentan-2-ol}$.

The functional class name of this alcohol is $1-methylbutylalcohol$.

The hydroxyl group is attached to a secondary carbon atom. Hence, it is a secondary alcohol.

The substitutive name of this alcohol is $\text{3-pentanol}\text{or}\text{pentan-3-ol}$.

The functional class name of this alcohol is $\text{1-ethylpropyl alcohol}$

The hydroxyl group is attached to a secondary carbon atom. Hence, it is a secondary alcohol.

The substitutive name of this alcohol is $\text{2-methyl-1-butanol}\text{or}\text{2-methylbutan-1-ol}$.

The functional class name of this alcohol is $2-methylbutylalcohol$.

The hydroxyl group is attached to a primary carbon atom. Hence, it is a primary alcohol.

The substitutive name of this alcohol is $\text{3-methyl-1-butanol}\text{or}\text{3-methylbutan-1-ol}$.

The functional class name of this alcohol is $\text{3-methylbutyl}\text{alcohol}$

The hydroxyl group is attached to a primary carbon atom. Hence, it is a primary alcohol.

The substitutive name of this alcohol is 2-methyl-2-butanol.

The functional class name of this alcohol is 1,1-dimethylpropanol.

The hydroxyl group is attached to a tertiary carbon atom. Hence, it is a tertiary alcohol.

The substitutive name of this alcohol is $\text{3-methyl-2-butanol}\text{or}\text{3-methylbutan-2-ol}$

The functional class name of this alcohol is $1,2-dimethylpropylalcohol$

The hydroxyl group is attached to a secondary carbon atom. Hence, it is a secondary alcohol.

The substitutive name of this alcohol is $\text{2,2-dimethyl-1-propanol or 2,2-dimethylpropan-1-ol}$.

The functional class name of this alcohol is $2,2-dimethylpropylalcohol$.

The hydroxyl group is attached to a primary carbon atom. Hence, it is a primary alcohol.

Conclusion

The structural formulas for the constitutionally isomeric alcohols of molecular formula ${\text{C}}_{\text{5}}{\text{H}}_{\text{12}}\text{O}$ are written by varying the positions of different groups in the compound.