Question

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

A

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

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B

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

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C

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

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D

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

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Solution

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

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