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Chapter 5: Problem 23

Which alkenes exist as pairs of cis, trans isomers? For each that does, draw the trans isomer. (a) \(\mathrm{CH}_{2}=\mathrm{CHBr}\) (b) \(\mathrm{CH}_{3} \mathrm{CH}=\mathrm{CHBr}\) (c) \(\mathrm{BrCH}=\mathrm{CHBr}\) (d) \(\left(\mathrm{CH}_{\mathrm{s}}\right)_{2} \mathrm{C}=\mathrm{CHCH}_{3}\) (e) \(\left(\mathrm{CH}_{5}\right)_{2} \mathrm{CHCH}=\mathrm{CHCH}_{3}\)

Short Answer

Expert verified
#Answer# Among the given alkenes, only (b) \(\mathrm{CH}_{3} \mathrm{CH}=\mathrm{CHBr}\) and (c) \(\mathrm{BrCH}=\mathrm{CHBr}\) can exist as pairs of cis, trans isomers. Their trans isomers are: (b) \(\mathrm{CH}_{3} \mathrm{CHCH} \equiv \mathrm{CHBr}\) (c) \(\mathrm{BrCH} \equiv \mathrm{CHBr}\)

Step by step solution

01

(a) Analyzing \(\mathrm{CH}_{2}=\mathrm{CHBr}\)

This alkene does not have two different groups on either carbon atom of the double bond. In fact, it lacks any groups on the first carbon. Therefore, it cannot exhibit cis, trans isomerism.
02

(b) Analyzing \(\mathrm{CH}_{3} \mathrm{CH}=\mathrm{CHBr}\)

This alkene has two different groups on each carbon atom of the double bond: a hydrogen atom and either a methyl group or a bromine atom. Thus, it can exist as a pair of cis, trans isomers.
03

(b) Drawing the trans isomer of \(\mathrm{CH}_{3} \mathrm{CH}=\mathrm{CHBr}\)

To draw the trans isomer, we will have the two larger substituents (the methyl group and the bromine atom) on opposite sides of the double bond. The structure will be: \(\mathrm{CH}_{3} \mathrm{CHCH} \equiv \mathrm{CHBr}\)
04

(c) Analyzing \(\mathrm{BrCH}=\mathrm{CHBr}\)

This alkene has two different groups (hydrogen and bromine) on each carbon atom of the double bond. Thus, it can exist as a pair of cis, trans isomers.
05

(c) Drawing the trans isomer of \(\mathrm{BrCH}=\mathrm{CHBr}\)

To draw the trans isomer, we will have the two larger substituents (the bromine atoms) on opposite sides of the double bond. The structure will be: \(\mathrm{BrCH} \equiv \mathrm{CHBr}\)
06

(d) Analyzing \(\left(\mathrm{CH}_{\mathrm{s}}\right)_{2} \mathrm{C}=\mathrm{CHCH}_{3}\)

This alkene does not meet the requirement for cis, trans isomerism, as it has identical groups (two methyl groups) on one of the carbon atoms of the double bond. Hence, it cannot exhibit cis, trans isomerism.
07

(e) Analyzing \(\left(\mathrm{CH}_{5}\right)_{2} \mathrm{CHCH}=\mathrm{CHCH}_{3}\)

This structure is not a valid chemical structure, as there is no such thing as a \(\mathrm{CH}_{5}\) group. It is likely a typographical error.

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Most popular questions from this chapter

Bromine adds to cis and trans-2-butene to give different diastereomers of 2,3 -dibromobutane. What does this say about the mode of addition of bromine to this alkene?

Draw structural formulas for these alkenes. (a) trans-2-Methyl-3-hexene (b) 2-Methyl-2-hexene (c) 2-Methyl-1-butene (d) S-Ethyl-3-methyl-1-pentene (e) 2,3-Dimethyl-2-butene (f) cis-2-Pentene (g) (Z)-1-Chloropropene (h) S-Methylcyclohexene (i) 1-Isopropyl-4-methylcyclohexene (j) (E)-2,6-Dimethyl-2,6-octadiene (k) 3-Cyclopropyl-1-propene (1) Cyclopropylethene (m) 2-Chloropropene (n) Tetrachloroethylene (o) 1-Chlorocyclohexene

Name and draw structural formulas for all alkenes with the molecular formula \(\mathrm{C}_{5} \mathrm{H}_{10}\). As you draw these alkenes, remember that cis and trans isomers are different compounds and must be counted separately.

\(\beta\)-Ocimene, a triene found in the fragrance of cotton blossoms and several essential oils, has the IUPAC name (Z)-3,7-dimethyl- \(1,3,6\)-octatriene. Draw a structural formula for \(\beta\)-ocimene.

Which alkenes show cis, trans isomerism? For each alkene that does, draw the transisomer. (a) 2-Pentene (b) 2-Methyl-2-pentene (c) 3-Methyl-2-pentene
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