Textbook Question
Name the following halogenated compounds according to the IUPAC rules of nomenclature.
(c)
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4. Alkanes and Cycloalkanes
Cis vs Trans
2:47 minutesProblem 2a
Textbook Question
Identify the following alkenes as E or Z, if appropriate.
(a) 
Verified step by step guidance1
Step 1: Understand the E/Z nomenclature. The E/Z system is used to describe the stereochemistry of alkenes. It is based on the Cahn-Ingold-Prelog priority rules, which assign priorities to the groups attached to the double-bonded carbons.
Step 2: Identify the two groups attached to each carbon of the double bond. For each carbon, determine the priority of the groups based on atomic number. The group with the higher atomic number gets the higher priority.
Step 3: Compare the positions of the higher-priority groups on each side of the double bond. 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: Apply the priority rules to the specific alkene in question. Carefully analyze the substituents on each carbon of the double bond and assign priorities.
Step 5: Based on the relative positions of the higher-priority groups, determine whether the alkene is E or Z. Ensure that you clearly document your reasoning for the assignment.
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Video duration:
2mKey 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. If the highest priority groups on each carbon are on the same side, the configuration is Z; if they are on opposite sides, it is E.
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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, making it essential to analyze their configurations for proper identification.
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