Question

Which of the following is the correct structure of 4-bromo-3-methyl but-1-ene?

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

Answer 1

The correct option is C

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

Explanation for the correct options:

(C) ${\mathrm{CH}}_2=\mathrm{CH}-\mathrm{CH}\left({\mathrm{CH}}_3\right)-{\mathrm{CH}}_2\mathrm{Br}$

• $\mathrm{Br}-$is attached to the $\mathrm{C}4$ position of the chain.
• The methyl group is attached to the $\mathrm{C}3$ position of the carbon chain.
• The double bond is present between $\mathrm{C}1$and $\mathrm{C}2$ position.
• So this chain represents the structure of 4-bromo-3-methyl but-1-ene.

Explanation for the incorrect options:

(A) $\mathrm{Br}-\mathrm{CH}=\mathrm{C}{\left({\mathrm{CH}}_3\right)}_2$

• This chain represents the structure of propene.
• $\mathrm{Br}-\mathrm{CH}=\mathrm{C}{\left({\mathrm{CH}}_3\right)}_2$ does not represent the structure of 4-bromo-3-methyl but-1-ene.
• The IUPAC name of this chain is 1-bromo-2-methylprop-1-ene.

(B) ${\mathrm{CH}}_3-\mathrm{C}\left({\mathrm{CH}}_3\right)={\mathrm{CHCH}}_2-\mathrm{Br}$

• This is the structure of butene where double in present in $\mathrm{C}2$ position.
• So it does not represent the structure of 4-bromo-3-methyl but-1-ene.
• The IUPAC name of this chain is 1-bromo-3-methyl but-2-ene.

(D) ${\mathrm{CH}}_2=\mathrm{C}\left({\mathrm{CH}}_3\right){\mathrm{CH}}_2{\mathrm{CH}}_2\mathrm{Br}$

• This is the structure of butene where the methyl group is present in $\mathrm{C}2$ position.
• So it does not represent the structure of 4-bromo-3-methyl but-1-ene.
• The IUPAC name of this chain is 4-bromo-2-methyl butene.

Hence, option (C) is correct., ${\mathrm{CH}}_2=\mathrm{CH}-\mathrm{CH}\left({\mathrm{CH}}_3\right)-{\mathrm{CH}}_2\mathrm{Br}$ is the correct structure of 4-bromo-3-methyl but-1-ene.