Textbook Question
Write structural formulas for the following compounds (includes both old- and new-style names).
g. 5,5-dibromo-4-phenylcyclooct-1-yne
h. (E)-6-ethyloct-2-en-4-yne
i.1,4-heptadiyne
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4. Alkanes and Cycloalkanes
Cis vs Trans
3:17 minutesProblem 2c
Textbook Question
Identify the following alkenes as E or Z, if appropriate.
(c) 
Verified step by step guidance1
Step 1: Identify the double bond in the structure. The double bond is located between the two carbon atoms in the upper part of the molecule.
Step 2: Assign priorities to the substituents on each carbon of the double bond using the Cahn-Ingold-Prelog priority rules. Higher atomic numbers take precedence, and if the atoms directly attached are the same, move outward to the next set of atoms.
Step 3: For the left carbon of the double bond, the substituents are the cyclopentyl group and a hydrogen atom. The cyclopentyl group has higher priority because it is a larger group compared to hydrogen.
Step 4: For the right carbon of the double bond, the substituents are the ethyl group and a hydrogen atom. The ethyl group has higher priority because it is larger than hydrogen.
Step 5: Determine the spatial arrangement of the higher-priority groups. If the higher-priority groups are on the same side of the double bond, the configuration is Z (zusammen). If they are on opposite sides, the configuration is E (entgegen).
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Video duration:
3mKey Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
E/Z Configuration
E/Z configuration is a method used to describe the stereochemistry of alkenes based on the priority of substituents attached to the double bond. The 'E' (entgegen) designation indicates that the highest priority groups are on opposite sides of the double bond, while 'Z' (zusammen) indicates they are on the same side. This system is crucial for understanding the geometric isomerism in alkenes.
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E/Z Diastereoisomerism
Cahn-Ingold-Prelog Priority Rules
The Cahn-Ingold-Prelog priority rules are used to assign priorities to the substituents attached to the double bond in alkenes. The priority is determined based on atomic number; the higher the atomic number of the atom directly attached to the double bond, the higher the priority. If the first atoms are the same, the comparison continues to the next atoms in the substituent chain until a difference is found.
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Stereoisomerism
Stereoisomerism refers to the phenomenon where compounds have the same molecular formula and connectivity of atoms but differ in the spatial arrangement of their atoms. In alkenes, this can lead to different physical and chemical properties, making it essential to identify whether a compound is E or Z. Understanding stereoisomerism is fundamental in organic chemistry, particularly in reactions involving alkenes.
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01:58Determining when molecules are stereoisomers.
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