Textbook Question
1. Determine which of the following compounds show cis-trans isomerism.
2. Draw and name the cis and trans (or Z and E) isomers of those that do.
a. hex-3-ene
b.buta-1,3-diene
4. Alkanes and Cycloalkanes
Cis vs Trans
6:45 minutesProblem 8e,f
Textbook Question
Some of the following examples can show geometric isomerism, and some cannot. For the ones that can, draw all the geometric isomers, and assign complete names using the E-Z system.
e. 3-ethyl-5-methyloct-3-ene
f. 3,7-dichloroocta-2,5-diene
Verified step by step guidance1
Step 1: Understand geometric isomerism. Geometric isomerism occurs due to restricted rotation around a double bond, leading to different spatial arrangements of substituents. The E-Z system is used to describe these arrangements based on the priority of groups attached to the double bond.
Step 2: Analyze the structure of 3-ethyl-5-methyloct-3-ene. Identify the double bond at the 3rd position and check the substituents on each carbon involved in the double bond. Determine if the substituents allow for geometric isomerism.
Step 3: For 3-ethyl-5-methyloct-3-ene, if geometric isomerism is possible, draw the possible isomers. Assign priorities to the substituents using the Cahn-Ingold-Prelog priority rules, and label the isomers as E or Z based on the arrangement of the highest priority groups.
Step 4: Analyze the structure of 3,7-dichloroocta-2,5-diene. Identify the double bonds at the 2nd and 5th positions and check the substituents on each carbon involved in these double bonds. Determine if geometric isomerism is possible for each double bond.
Step 5: For 3,7-dichloroocta-2,5-diene, if geometric isomerism is possible, draw the possible isomers for each double bond. Assign priorities to the substituents using the Cahn-Ingold-Prelog priority rules, and label the isomers as E or Z based on the arrangement of the highest priority groups for each double bond.
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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, also known as cis-trans isomerism, occurs due to restricted rotation around a double bond, leading to different spatial arrangements of substituents. In alkenes, this isomerism is possible when each carbon of the double bond has two different groups attached, allowing for distinct configurations.
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E-Z Nomenclature System
The E-Z system is a method for naming geometric isomers based on the priority of substituents attached to the double-bonded carbons. 'E' (entgegen) indicates opposite sides, while 'Z' (zusammen) indicates the same side. Priorities are determined using the Cahn-Ingold-Prelog rules, which consider atomic number and connectivity.
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Substituent Positioning in Alkenes
Understanding the positioning of substituents in alkenes is crucial for identifying potential geometric isomers. The position is indicated by numbers in the compound's name, which correspond to the carbon atoms in the longest chain. Correct identification of these positions helps determine if geometric isomerism is possible.
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