Textbook Question
Which of the following alkenes are E and which are Z?
(c)
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4. Alkanes and Cycloalkanes
Cis vs Trans
3:36 minutesProblem 12a
Textbook Question
Which of the following alkenes are E and which are Z?
(a) 
Verified step by step guidance1
Step 1: Recall the Cahn-Ingold-Prelog priority rules. These rules are used to assign priorities to the groups attached to the double-bonded carbons in the alkene. The group with the higher atomic number gets the higher priority. If there is a tie, move outward to the next set of atoms until a difference is found.
Step 2: Identify the two groups attached to each carbon of the double bond in the given alkene. Assign priorities to these groups based on the Cahn-Ingold-Prelog rules.
Step 3: Determine the relative positions of the higher-priority groups on each carbon. If the higher-priority groups are on the same side of the double bond, the alkene is classified as Z (from the German word 'zusammen,' meaning together). If the higher-priority groups are on opposite sides, the alkene is classified as E (from the German word 'entgegen,' meaning opposite).
Step 4: Repeat the process for each alkene in the problem. Carefully analyze the structure of each alkene to ensure correct assignment of E or Z configuration.
Step 5: Summarize the results by labeling each alkene as either E or Z based on your analysis. Ensure that your assignments are consistent with the priority rules and the spatial arrangement of the groups.
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Video duration:
3mKey Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Alkene Geometry
Alkenes are hydrocarbons that contain at least one carbon-carbon double bond (C=C). The geometry around the double bond is planar, leading to two possible configurations: E (entgegen) and Z (zusammen). These configurations depend on the relative positions of the substituents attached to the double-bonded carbons.
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Cahn-Ingold-Prelog Priority Rules
To determine whether an alkene is E or Z, the Cahn-Ingold-Prelog priority rules are applied. These rules assign priority to substituents based on atomic number; the higher the atomic number, the higher the priority. The configuration is Z if the highest priority substituents are on the same side of the double bond and E if they are on opposite sides.
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Stereoisomerism
Stereoisomerism refers to the phenomenon where compounds have the same molecular formula and connectivity but differ in the spatial arrangement of atoms. In alkenes, stereoisomers can exist as E/Z isomers due to the restricted rotation around the double bond, leading to distinct physical and chemical properties.
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