(a)
Interpretation: The stereochemistry of given reaction is to be predicted.
Concept introduction: Cycloaddition reactions are pericyclic reactions that take place in two compounds containing pi bonds to form a cyclic compound. These reactions are concerted and stereospecific in nature. According to Woodward-Hoffmann rules, the polyene containing even number of bonds in thermal conditions undergoes reaction in antrafacial fashion and polyene containing odd number of bonds undergo reaction in suprafacial fashion. The total number of bonds present in the
(b)
Interpretation: The stereochemistry of given reaction is to be predicted.
Concept introduction: Electrocyclic reactions involve ring opening or ring closure in a conjugated polyene. According to Woodward-Hoffmann rules, the polyene containing even number of bonds in photochemical conditions undergoes reaction in disrotatory fashion and polyene containing odd number of bonds undergo reaction in conrotatory fashion.
(c)
Interpretation: The stereochemistry of given reaction is to be predicted.
Concept introduction: Cycloaddition reactions are pericyclic reactions that take place in two compounds containing pi bonds to form a cyclic compound. These reactions are concerted and stereospecific in nature. According to Woodward-Hoffmann rules, the polyene containing even number of bonds in photochemical conditions undergoes reaction in suprafacial fashion and polyene containing odd number of bonds undergo reaction in antrafacial fashion. The total number of bonds present in the alkenes is considered.
(d)
Interpretation: The stereochemistry of given reaction is to be predicted.
Concept introduction: Sigmatropic rearrangements are pericyclic reactions which takes place by concerted mechanism. In these rearrangements migration of sigma bond takes place. According to Woodward-Hoffmann rules, the total number of electron pairs in sigma bond that is broken and the pi bonds that rearrange. The polyene containing even number of electron pairs and bonds in thermal conditions undergoes reaction in antrafacial fashion and polyene containing odd number of electron pairs and bonds undergo reaction in suprafacial fashion.
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Chapter 25 Solutions
ORGANIC CHEMISTRY
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