Textbook Question
For the compound 1-ethyl-3-isopropylcyclopentane,
(a) draw two different cis and two different trans isomers.
4. Alkanes and Cycloalkanes
Cis vs Trans
3:57 minutesProblem 41
Textbook Question
Label each structure as Z, E, or neither.
(a) 
(b) 
(c) 
(d) 
Verified step by step guidance1
Identify the highest priority group on each carbon of the double bond using the Cahn-Ingold-Prelog priority rules. The priority is determined by the atomic number of the atoms directly attached to the double bond carbons.
For structure (a), compare the groups attached to each carbon of the double bond. On the left carbon, the groups are H and CH3, with CH3 having higher priority. On the right carbon, the groups are CH3 and Br, with Br having higher priority.
For structure (b), compare the groups attached to each carbon of the double bond. On the left carbon, the groups are HO and CH3, with HO having higher priority. On the right carbon, the groups are CH2CH3 and CH3, with CH2CH3 having higher priority.
For structure (c), compare the groups attached to each carbon of the double bond. On the left carbon, the groups are H and Ph, with Ph having higher priority. On the right carbon, the groups are Ph and CH3, with Ph having higher priority.
For structure (d), compare the groups attached to each carbon of the double bond. On the left carbon, the groups are H and CH3, with CH3 having higher priority. On the right carbon, the groups are CH2OH and COOH, with COOH having higher priority.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Geometric Isomerism
Geometric isomerism occurs in alkenes due to the restricted rotation around the carbon-carbon double bond. This leads to two distinct configurations: cis (Z) where substituents are on the same side, and trans (E) where they are on opposite sides. Understanding this concept is crucial for identifying and labeling the structures in the question.
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Cis-Trans Nomenclature
Cis-trans nomenclature is a system used to describe the spatial arrangement of groups attached to the double-bonded carbons in alkenes. The 'Z' (from the German 'zusammen') designation indicates that the highest priority substituents are on the same side, while 'E' (from 'entgegen') indicates they are on opposite sides. This nomenclature is essential for correctly labeling the structures presented.
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Priority Rules (Cahn-Ingold-Prelog)
The Cahn-Ingold-Prelog priority rules are used to determine the priority of substituents attached to the double-bonded carbons in alkenes. By comparing the atomic numbers of the atoms directly attached to the double-bonded carbons, one can assign priorities that help in identifying whether the isomer is Z or E. Mastery of these rules is necessary for accurate labeling of the structures.
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