30. There is another approach to predicting the stereochemistry of electrocyclic ring closures. One simply looks at the ends of the HOMO to conclude the proper direction for rotation of the bond by creating in-phase interactions during closure. Show that this method also predicts conrotatory closure for butadiene and disrotatory closure for hexatriene. 31. Predict the thermally allowed products of the following two mraction

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30. There is another approach to predicting the stereochemistry of electrocyclic ring closures. One simply looks at the ends
of the HOMO to conclude the proper direction for rotation of the bond by creating in-phase interactions during closure.
Show that this method also predicts conrotatory closure for butadiene and disrotatory closure for hexatriene.
31. Predict the thermally allowed products of the following two reactions.
2 D
O
32. The following reaction is known as the Carroll rearrangement. Write a mechanism for this reaction. What pericyclic
reactions involved?
RR
H
Base
Heal
O
33. At first glance, the following reaction appears to be a [2 + 2] cycloaddition of a single double bond from cyclopentadiene
with the C=C double bond of diphenylketene. However, it has been experimentally shown that the product actually
results from two more conventional pericyclic reactions. Show by writing an alternative mechanism what these two
reactions must be.
I
Ph
Ph
Ph
Ph-
CO₂
O
34. The retroene reaction is, as the name implies, the reverse of an ene reaction. Show how the following reaction conforms to
this name. Explain the cis stereochemistry in the product.
A
35. A rare, but sometimes observed, class of pericyclic reactions is called atom transfer or group transfer reactions. A single
example is given below, where two hydrogens are transferred to an alkene in a concerted single-step reaction. Using ethyl-
ene and ethane as models for the alkene and alkane portion of this reaction, draw an orbital correlation diagram for this
reaction. Is it allowed or forbidden? Similarly, analyze the reaction using an FMO approach, and lastly examine aromatic
transition state theory and the generalized pericyclic selection rule.
Ring-opening
36. Figure 15.9 defined suprafacial and antarafacial interactions of a lone pair in ap orbital (called an o component).
Using these definitions, predict if the ring-opening of the cyclopropyl anion shown below will occur in a conrotatory
or disrotatory fashion. What will be the stereochemistry of the product?
arrow pushing shows a cvelic
Transcribed Image Text:30. There is another approach to predicting the stereochemistry of electrocyclic ring closures. One simply looks at the ends of the HOMO to conclude the proper direction for rotation of the bond by creating in-phase interactions during closure. Show that this method also predicts conrotatory closure for butadiene and disrotatory closure for hexatriene. 31. Predict the thermally allowed products of the following two reactions. 2 D O 32. The following reaction is known as the Carroll rearrangement. Write a mechanism for this reaction. What pericyclic reactions involved? RR H Base Heal O 33. At first glance, the following reaction appears to be a [2 + 2] cycloaddition of a single double bond from cyclopentadiene with the C=C double bond of diphenylketene. However, it has been experimentally shown that the product actually results from two more conventional pericyclic reactions. Show by writing an alternative mechanism what these two reactions must be. I Ph Ph Ph Ph- CO₂ O 34. The retroene reaction is, as the name implies, the reverse of an ene reaction. Show how the following reaction conforms to this name. Explain the cis stereochemistry in the product. A 35. A rare, but sometimes observed, class of pericyclic reactions is called atom transfer or group transfer reactions. A single example is given below, where two hydrogens are transferred to an alkene in a concerted single-step reaction. Using ethyl- ene and ethane as models for the alkene and alkane portion of this reaction, draw an orbital correlation diagram for this reaction. Is it allowed or forbidden? Similarly, analyze the reaction using an FMO approach, and lastly examine aromatic transition state theory and the generalized pericyclic selection rule. Ring-opening 36. Figure 15.9 defined suprafacial and antarafacial interactions of a lone pair in ap orbital (called an o component). Using these definitions, predict if the ring-opening of the cyclopropyl anion shown below will occur in a conrotatory or disrotatory fashion. What will be the stereochemistry of the product? arrow pushing shows a cvelic
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