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Exam 28: Pericyclic Reactions

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Question 1

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Predict the major organic product and show stereochemistry where relevant.

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11edaded_7d20_5af1_a31a_371359ca4399_TBMC1048_00 The reaction is a ring-opening electrocyclic reaction. There are six electrons involved in the reaction and it is heated, so the reaction will be disrotatory. The two ethyl substituents can be either cis/cis or trans/trans. The cis/cis would be highly hindered, so the trans/trans isomer predominates.

Question 2

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Classify the sigmatropic reaction with bracketed numbers.

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This is a [2,3] sigmatropic re...

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Question 3

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Sketch the molecular orbitals for 1,3-pentadiene. Fill in the number of electrons in each molecular orbital, then identify the HOMO and LUMO. How many nodes are in each molecular orbital?

Draw curved-arrow mechanism showing how this transformation occurs.

This transformation can occur through two pericyclic reactions. Outline a synthesis for the transformation.

Given the starting material and conditions, identify the type of pericyclic reaction, the number of electrons involved in the reaction, and draw the major organic product. Clearly show stereochemistry, if applicable.

Deduce the starting materials needed to synthesize this compound.

Classify the sigmatropic reaction with bracketed numbers.

Given the starting material and conditions, identify the type of pericyclic reaction, the number of electrons involved in the reaction, and draw the major organic product. Clearly show stereochemistry, if applicable.

Which conditions should you use to perform the reaction and why?

Outline a synthetic sequence to give this transformation. Hint: A sigmatropic rearrangement is a key step.

Give the product for a [1,5] deuterium shift for this structure:

Classify the reaction:

Draw a curved-arrow mechanism showing how the alcohol is transformed to the ketone.

Consider the carbocation: a. How many pi molecular orbitals are there? b. Classify each MO as symmetric or antisymmetric. c. Which MOs are bonding and antibonding? d. Which MOs are the HOMO and LUMO?

Given the starting material and conditions, identify the type of pericyclic reaction, the number of electrons involved in the reaction, and draw the major organic product. Clearly show stereochemistry, if applicable.

Classify the reaction:

Outline a synthesis for this transformation. A key step should be a [2,2] or [4,2] cycloaddition.

Predict the major organic products in the boxes and show stereochemistry where relevant.

Two ethylene molecules can undergo a [2+2] cycloaddition, but only under photochemical conditions. Explain this difference in reactivity.