Question

Which one of the following is $1-\mathrm{bromo}-3-\mathrm{methyl}\mathrm{butane}$?

• A. ${\left({\mathrm{CH}}_3\right)}_2{\mathrm{CHCH}}_2{\mathrm{CH}}_2\mathrm{Br}$
• B. ${\left({\mathrm{CH}}_3\right)}_2\mathrm{C}\left(\mathrm{Br}\right){\mathrm{CH}}_2{\mathrm{CH}}_3$
• C. ${\left({\mathrm{CH}}_3\right)}_2\mathrm{CHCH}\left(\mathrm{Br}\right){\mathrm{CH}}_3$
• D. ${{\mathrm{CH}}_3\left({\mathrm{CH}}_2\right)}_5\mathrm{Br}$

Answer 1

The correct option is A

${\left({\mathrm{CH}}_3\right)}_2{\mathrm{CHCH}}_2{\mathrm{CH}}_2\mathrm{Br}$

Explanation for the correct option

(A) ${\mathbf{\left(}{\mathbf{CH}}_{\mathbf{3}}\mathbf{\right)}}_{\mathbf{2}}{\mathbf{CHCH}}_{\mathbf{2}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{Br}$

IUPAC System of Nomenclature

• Find the carbon chain that is the longest.
• All of the substituents must be identified.
• From the end of the parent chain, count the carbons until the substituents have the lowest number.
• A prefix indicates how many times a substituent group appears (di, tri, tetra, etc.).
• A suffix or other element(s) indicates the presence of functional groups in the compound.
• If there are two or more substituents, they are listed alphabetically by base name.

$\mathbf{1}\mathbf{-}\mathbf{bromo}\mathbf{-}\mathbf{3}\mathbf{-}\mathbf{methyl}\mathbf{}\mathbf{butane}$

• Carbon has the longest continuous chain of carbon atoms in the molecule, with four.
• As a result, butane should be included in the name.
• One methyl group is connected to the compound's third position.
• So because carbon includes one bromine, the name should begin with $1-\mathrm{bromo}$.
• Hence, the IUPAC name of ${\left({\mathrm{CH}}_3\right)}_2{\mathrm{CHCH}}_2{\mathrm{CH}}_2\mathrm{Br}$ is $1-\mathrm{bromo}-3-\mathrm{methyl}\mathrm{butane}$.

Explanation for incorrect options

(B) ${\mathbf{\left(}{\mathbf{CH}}_{\mathbf{3}}\mathbf{\right)}}_{\mathbf{2}}\mathbf{C}\mathbf{\left(}\mathbf{Br}\mathbf{\right)}{\mathbf{CH}}_{\mathbf{2}}{\mathbf{CH}}_{\mathbf{3}}$

• The IUPAC name of ${\left({\mathrm{CH}}_3\right)}_2\mathrm{C}\left(\mathrm{Br}\right){\mathrm{CH}}_2{\mathrm{CH}}_3$ is $2-\mathrm{bromo}-2-\mathrm{methyl}\mathrm{butane}$.

(C) ${\mathbf{\left(}{\mathbf{CH}}_{\mathbf{3}}\mathbf{\right)}}_{\mathbf{2}}\mathbf{CHCH}\mathbf{\left(}\mathbf{Br}\mathbf{\right)}{\mathbf{CH}}_{\mathbf{3}}$

• The IUPAC name of ${\left({\mathrm{CH}}_3\right)}_2\mathrm{CHCH}\left(\mathrm{Br}\right){\mathrm{CH}}_3$ is $2-\mathrm{bromo}-3-\mathrm{methyl}\mathrm{butane}$.

(D) ${{\mathbf{CH}}_{\mathbf{3}}\mathbf{\left(}{\mathbf{CH}}_{\mathbf{2}}\mathbf{\right)}}_{\mathbf{5}}\mathbf{Br}$

• The IUPAC name of ${{\mathrm{CH}}_3\left({\mathrm{CH}}_2\right)}_5\mathrm{Br}$ is $1-\mathrm{bromohexane}$.

Therefore, the correct option is (A) ${\mathbf{\left(}{\mathbf{CH}}_{\mathbf{3}}\mathbf{\right)}}_{\mathbf{2}}{\mathbf{CHCH}}_{\mathbf{2}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{Br}$.