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Mobile App Chapter 27: Q 33. (page 1100)
Question: Draw the product of each electrocyclic reaction.
a. the thermal electrocyclic ring closure of (2E,4Z,6Z)-nona-2,4,6-triene
b. the photochemical electrocyclic ring closure of (2E,4Z,6Z)-nona-2,4,6-triene
c. the thermal electrocyclic ring-opening of cis-5-ethyl-6-methylcyclohexa-1,3-diene
d. the photochemical electrocyclic ring-opening of trans-5-ethyl-6-methylcyclohexa-1,3- diene
Short Answer
Product of electrocyclic reaction:
Step by step solution
Selection rule for electrocyclic reactions
Thermal electrocyclic reactions having 4n electrons are allowed when they proceed by con-rotation.
Thermal electrocyclic reactions having 4n+2 electrons are allowed when they proceed by dis-rotation.
The rules for photochemical electrocyclic reactions are the opposite of thermal electrocyclic reactions
The product of the electrocyclic reaction
(a)
- Electrocyclic ring closure reaction occurs with three conjugated double bonds.
- Disrotatory under thermal conditions
- From Woodward-Hoffmann's rules, thermal electrocyclic reactions involving 4n+2 electrons are disrotatory.
Therefore, the product formation can be represented as:
Product of electrocyclic reaction
(b)
- Electrocyclic ring closure reaction occurs with three conjugated double bonds.
- Conrotatory under photochemical conditions
- From Woodward-Hoffmann's rules, photochemical electrocyclic reactions involving 4n+2 electrons are conrotatory.
Therefore, the product formation can be represented as:
Product of electrocyclic reaction
(c)
- Electrocyclic ring closure reaction occurs under thermal conditions.
Therefore, the product formation can be represented as:
Product of electrocyclic reaction
(d)
- Electrocyclic ring closure reaction occurs under photochemical conditions.
Therefore, the product formation can be represented as:
Product of electrocyclic reaction
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