Chapter 5, Problem 20P

Interpretation Introduction

Interpretation:

The IUPAC names of the given compounds are to be determined.

Concept introduction:

The halogen is treated as substituent on an alkane chain, by the substitutive nomenclature of alkyl halides. The direction that gives the substituted carbon the lower number, is the direction in which the carbon chain is numbered.

The two substituents are considered of equal rank, when both halogen and an alkyl substituent are on the same carbon chain. The substituent nearer the end of the chain is given the lower number.

Answer to Problem 20P

Solution:

$\text{1- Bromo - 4 - methylpentane}$

$\text{4 - Methyl -1- pentanol}$

$\text{2 - Bromo -1,1,1- trichloroethane}$

$\text{1 - Bromo -1,2,2- trichloroethane}$

$\text{2,2,2-Trifluoro-1-ethanol}$

$\text{Cis-3-tert-Butylcyclohexan-1-ol}$

$\text{2-Cyclopentylpropan-2-ol}$

$\text{5-Bromo-2,3-dimethylhexane}$

$\text{4,5-Dimethylhexan-2-ol}$

Explanation of Solution

(a) ${({\text{CH}}_3)}_2{\text{CHCH}}_2{\text{CH}}_2{\text{CH}}_2\text{Br}$

${({\text{CH}}_3)}_2{\text{CHCH}}_2{\text{CH}}_2{\text{CH}}_2\text{Br}$ is converted to the structural formula as shown below:

In this structure, the longest carbon chain is “pentane,” which contains $5$ carbon atoms. There are two substituents attached. The chain is numbered such that these substituents get the lowest numbers. The bromine atom and the methyl group are considered of equal rank. The bromine atom is nearer to the end of the chain. Hence the pentane chain is numbered such that the carbon attached to bromine gets the number $1$. The methyl group is attached to the $\text{C4}$ carbon atom.

Therefore, the IUPAC name of the given structure is $\text{1- Bromo - 4 - methylpentane}$.

(b) ${({\text{CH}}_3)}_2{\text{CHCH}}_2{\text{CH}}_2{\text{CH}}_2\text{OH}$

${({\text{CH}}_3)}_2{\text{CHCH}}_2{\text{CH}}_2{\text{CH}}_2\text{OH}$ is converted to the structural formula as shown below:

In this structure, the longest carbon chain is “pentane,” which contains $5$ carbon atoms. The chain is numbered such that the hydroxyl group get the lowest number. Hence the pentane chain is numbered such that the carbon attached to the hydroxyl group gets the number $1$. The methyl group is attached to the $\text{C4}$ carbon atom.

Therefore, the IUPAC name of given structure is $\text{4 - Methyl -1- pentanol}$.

(c) ${\text{Cl}}_{\text{3}}{\text{CCH}}_{\text{2}}\text{Br}$

${\text{Cl}}_{\text{3}}{\text{CCH}}_{\text{2}}\text{Br}$ is converted to the structural formula as shown below:

In this structure, the longest carbon chain is “ethane,” which contains $2$ carbon atoms. Three chlorine atoms are attached to one carbon atom while one bromine atom is attached to the other carbon atom. The chain is numbered such that the carbon atom attached to the three chlorine atoms gets the lowest number. Hence the ethane chain is numbered such that the carbon attached to the chlorine atoms gets the number $1$.

Therefore, the IUPAC name of given structure is $\text{2 - Bromo -1,1,1- trichloroethane}$.

(d)

The given compound is converted to the structural formula as shown below:

In the given structure, the longest possible parent chain is “ethane,” which contains $2$ carbon atoms. Two chlorine atoms are attached to one carbon atom while one bromine atom and one chlorine atom are attached to the other carbon atom. Both the carbon atoms are each attached to two halogen atoms. Hence the chain is numbered such that the carbon atom attached to the bromine atom get the lowest number since bromine comes before chlorine alphabetically.

Therefore, the IUPAC name of given structure is $\text{1 - Bromo -1,2,2- trichloroethane}$.

(e) ${\text{CF}}_{\text{3}}{\text{CH}}_{\text{2}}\text{OH}$

${\text{CF}}_{\text{3}}{\text{CH}}_{\text{2}}\text{OH}$ is converted to the structural formula as shown below:

In the given structure, the longest possible parent chain is “ethane,” which contains $2$ carbon atoms. One carbon atom is attached to a hydroxyl group while the other carbon atom is attached to three fluorine atoms. Hydroxyl groups take precedence over halogens in determining the direction in which a carbon chain is numbered. Hence, the carbon atom attached to the hydroxyl group is numbered $1$. Therefore, the IUPAC name of the compound is $\text{2,2,2-Trifluoro-1-ethanol}$.

(f)

In the given structure, the parent chain is cyclic and has six carbon atoms. Hence the parent alkane is cyclohexane. One carbon atom is attached to a hydroxyl group. Hydroxyl groups take precedence over alkyl groups in determining the direction in which a carbon chain is numbered. Hence, the carbon atom attached to the hydroxyl group is numbered $1$. The carbon atom attached to the tertiary butyl group gets the number $3$. Both the groups are on the same side of the cyclohexane ring. Hence they are cis to each other as shown:

Thus, the IUPAC name of the compound is $\text{Cis-3-tert-Butylcyclohexan-1-ol}$.

(g)

In the given structure, a five member cyclopentane ring is present. There is a three carbon atom chain bearing the hydroxyl group. The propane chain becomes the parent since the hydroxyl group is attached to it. The cyclopentane ring is considered as substituent and attached to the second carbon of the propane chain as shown:

Thus, the IUPAC name of the given structure is $\text{2-Cyclopentylpropan-2-ol}$.

(h)

In the given structure, the longest possible parent chain is “Hexane,” which contains $6$ carbon atoms. There are three substituents attached. The chain is numbered such that these substituents get the lowest numbers. The bromine atom and the methyl group are considered of equal rank. Hence the pentane chain is numbered such that the methyl groups are attached to carbon atoms two and three while the bromine atom is attached to carbon number $5$.

The prefix di is used to indicate the presence of two methyl groups.

Thus, the IUPAC name of the given structure is $\text{5-Bromo-2,3-dimethylhexane}$.

(i)

In the given structure, the longest possible parent chain is “Hexane,” which contains $6$ carbon atoms. One carbon atom is attached to a hydroxyl group. Hydroxyl groups take precedence over alkyl groups in determining the direction in which a carbon chain is numbered. Hence, the hexane chain is numbered such that the carbon atom attached to the hydroxyl group gets the lowest number. The carbon atoms attached to the methyl groups get the numbers $\text{4 and 5}$ as shown:

Thus, the IUPAC name of the compound is $\text{4,5-Dimethylhexan-2-ol}$.