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Chapter 27: Q 55. (page 1103)

Question: Show how the following starting material is converted to the given product by a series of two pericyclic reactions. Account for the observed stereochemistry.

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01

Electrocyclic reaction

The reactions that involve the conversion of a pi bond of a conjugated system to a sigma bond or vice-versa are named electrocyclic reactions.

Conjugated systems involving an even number of pi electrons undergo conrotation, while conjugated systems with an odd number of pi electrons undergo disrotation under thermal conditions.

02

Preparation of the given product

The conversion of the starting material to the given product involves two main steps:

  • 8 pi electrocyclic ring-opening (conrotatory) and
  • 6 pi electrocyclic ring-opening (conrotatory).

The reactions are shown below.

Reactions involved in the formation of the product

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Most popular questions from this chapter

Question: A solution of 5-methylcyclopenta-1,3-diene rearranges at room temperature to a mixture containing 1-methyl-, 2-methyl-, and 5-methylcyclopenta-1,3-diene. (a) Show how both isomeric products are formed from the starting material by a sigmatropic rearrangement involving a C–H bond. (b) Explain why 2-methylcyclopenta-1,3-diene is not formed directly from 5-methylcyclopenta-1,3-diene by a [1,3] rearrangement.

Question: What product is formed when each compound in Problem 27.6 undergoes photochemical electrocyclic ring-opening or ring closure? Label each process as conrotatory or disrotatory and clearly indicate the stereochemistry around tetrahedral stereogenic centers and double bonds.

Question: Draw the product formed when each triene undergoes electrocyclic reaction under [1] thermal conditions, [2] photochemical conditions

Question: Classify each pericyclic reaction as an electrocyclic reaction, cycloaddition, or sigmatropic rearrangement. Indicate whether the stereochemistry is conrotatory, disrotatory, suprafacial, or antarafacial.

Question: (a) How many π molecular orbitals are present in deca-1,3,5,7,9-pentaene (CH2=CH-CH=CH-CH=CH-CH=CH-CH=CH2)? (b) How many are bonding MOs and how many are antibonding MOs ? (c) How many nodes are present in ψ1*? (d) How many nodes are present in ψ10*?
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