Diene and Allylic Systems Practice Problems (Answer Key)Carey, 8th Edition, Chapter 10

1. Give the appropriate starting compound(s) for each reaction.

2. Rank these molecules according to stability. Assign #1 to the most stable molecule and #6 to the least.

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Diene and Allylic Systems Practice Problems (Answer Key)Carey, 8th Edition, Chapter 10

3. Rank the compounds below based on stability of the thermodynamic product when each molecule is treated with lithium methanethiol in acetone. Give #1 to the molecule that yields the most stable product.

4. Draw the mechanism for each of these reactions. For the second reaction, specify which product is most likely the kinetic and which is likely the thermodynamic product.

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Diene and Allylic Systems Practice Problems (Answer Key)Carey, 8th Edition, Chapter 10

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Diene and Allylic Systems Practice Problems (Answer Key)Carey, 8th Edition, Chapter 10

5. Answer the following questions regarding the molecular orbitals of the molecule below.

We are only concerned with the π electrons in this conjugated system (Huckel approximation).

LUMO stands for: Lowest-energy Unoccupied Molecular Orbital

HOMO stands for: Highest-energy Occupied Molecular Orbital

A node is when there is a sign change (+ to -, or vice versa) between the atomic orbitals.

The more nodes that are present in a molecular orbital, the less stable it becomes.

In the molecule above…

…The most stable MO of this compound will have 0 nodes.

…The least stable MO of this compound will have 5 nodes.

In general, the maximum number of nodes for the MOs can be represented as τ−1, where τ is the number of atomic orbital that comprise the molecular orbital.

The number of possible molecular orbital (MO) combinations in this molecule is equal to 6, which is equal to the number of atomic orbitals of the conjugated chain.

Complete the following diagram below, which represents the possible MO combinations of atomic orbitals; do so in the order of increasing energy. Let shaded regions be of negative

charge. The first MO has been done.

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Diene and Allylic Systems Practice Problems (Answer Key)Carey, 8th Edition, Chapter 10

Based on the Aufbau Principle, electrons are placed into orbitals of increasing energy (i.e., start at lower energy levels and build upwards).

There is a total of 6 π electrons in the molecule of interest.

Place the π electrons into the appropriate molecular orbitals in the diagram above. Do this by placing arrows (↑ or ↑↓) on the bars to the right of the diagram. Label the LUMO and HOMO.

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Diene and Allylic Systems Practice Problems (Answer Key)Carey, 8th Edition, Chapter 10

6. Now for a variant of the MO question regarding a conjugated system. Answer the questions below regarding this compound:

There are 5 atomic orbitals in this conjugated system; hence, there will be 5 possible molecular orbitals.

There is a maximum of 4 nodes in this molecule.

Draw the MO-Overlap Diagram for this molecule, starting with the lowest-energy MO and increasing in energy to the least stable MO.

There are 4 π electrons in this conjugated system.

Distribute the π electrons into the appropriate MO’s in the diagram you drew above. Assign the HOMO and LUMO.

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Diene and Allylic Systems Practice Problems (Answer Key)Carey, 8th Edition, Chapter 10

7. Rank the following diene/dienophile pairs based on rate of reaction. Give #1 to the pair that would react the fastest.

8. Complete the following reactions.

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Diene and Allylic Systems Practice Problems (Answer Key)Carey, 8th Edition, Chapter 10

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