(a)
Interpretation:
For each of the given thermal electrocyclic reactions, the major product formed should be determined.
Concept introduction:
- Electrocyclic reaction is a concerted cyclization reaction of conjugated polyenes (π-system), in which one π-bond is converted into an σ-bond and remaining π-bonds shift their positions. Thereby the newly formed σ-bond connects the two ends of π-system to form a ring.
- The mechanism of the ring formation in the Electrocyclic reaction is drawn by using arrows representing the forming σ-bond and the shifting of π-bonds in the π-system of a polyene.
- The reaction conditions (thermal or photochemical) controls the product in such a way that the rotation for end lobes (ring closure) of the HOMO of conjugated (π-system) polyene.
- According to Woodward-Hoffmann rule for thermal and photochemical Electrocyclic reactions,
π-systems | Thermal | Photochemical |
4- π-electrons | Conrotatory | Disrotatory |
6- π-electrons | Disrotatory | Conrotatory |
- The mechanism for reverse of Electrocyclic reaction is drawn by using arrows representing the conversion of σ-bond to π-bond and the shifting of π-bonds in the π-system of a cyclic
alkene .
To determine: the major product formed for each of the given thermal electrocyclic reactions.
(b)
Interpretation:
For each of the given thermal electrocyclic reactions, the major product formed should be determined.
Concept introduction:
- Electrocyclic reaction is a concerted cyclization reaction of conjugated polyenes (π-system), in which one π-bond is converted into an σ-bond and remaining π-bonds shift their positions. Thereby the newly formed σ-bond connects the two ends of π-system to form a ring.
- The mechanism of the ring formation in the Electrocyclic reaction is drawn by using arrows representing the forming σ-bond and the shifting of π-bonds in the π-system of a polyene.
- The reaction conditions (thermal or photochemical) controls the product in such a way that the rotation for end lobes (ring closure) of the HOMO of conjugated (π-system) polyene.
- According to Woodward-Hoffmann rule for thermal and photochemical Electrocyclic reactions,
π-systems | Thermal | Photochemical |
4- π-electrons | Conrotatory | Disrotatory |
6- π-electrons | Disrotatory | Conrotatory |
- The mechanism for reverse of Electrocyclic reaction is drawn by using arrows representing the conversion of σ-bond to π-bond and the shifting of π-bonds in the π-system of a cyclic alkene.
To determine: the major product formed for each of the given thermal electrocyclic reactions.
(c)
Interpretation:
For each of the given thermal electrocyclic reactions, the major product formed should be determined.
Concept introduction:
- Electrocyclic reaction is a concerted cyclization reaction of conjugated polyenes (π-system), in which one π-bond is converted into an σ-bond and remaining π-bonds shift their positions. Thereby the newly formed σ-bond connects the two ends of π-system to form a ring.
- The mechanism of the ring formation in the Electrocyclic reaction is drawn by using arrows representing the forming σ-bond and the shifting of π-bonds in the π-system of a polyene.
- The reaction conditions (thermal or photochemical) controls the product in such a way that the rotation for end lobes (ring closure) of the HOMO of conjugated (π-system) polyene.
- According to Woodward-Hoffmann rule for thermal and photochemical Electrocyclic reactions,
π-systems | Thermal | Photochemical |
4- π-electrons | Conrotatory | Disrotatory |
6- π-electrons | Disrotatory | Conrotatory |
- The mechanism for reverse of Electrocyclic reaction is drawn by using arrows representing the conversion of σ-bond to π-bond and the shifting of π-bonds in the π-system of a cyclic alkene.
To determine: the major product formed for each of the given thermal electrocyclic reactions.
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