Chapter 12, Problem 12.26P

Interpretation Introduction

(a)

Interpretation:

The mechanism for the reaction that will take place when the given compound is treated with ${\text{CH}}_{\text{2}}{\text{N}}_{\text{2}}$ and irradiated with ultraviolet light is to be drawn.

Concept introduction:

Diazomethane, ${\text{CH}}_{\text{2}}{\text{N}}_{\text{2}}$, dissociates heterolytically into a carbene and a nitrogen molecule when irradiated with ultraviolet light. The carbene adds to the double bond, simultaneously forming bonds to both carbons of the double bond. This results in the formation of a cyclopropane ring.

The stereochemistry of the double bond is preserved in the addition. If the double bond has a cis relationship, then the two substituents end up on the same side of the cyclopropane ring. If the two substituents on the double bond are trans to each other, they end up on the opposite sides of the cyclopropane ring. This also determines the product distribution if the cyclic product is chiral. If the starting alkene is achiral and the product chiral, the product is a racemic mixture of enantiomers. If the starting alkene is also chiral, then an unequal mixture of enantiomers is produced.

Answer to Problem 12.26P

The mechanism for the reaction when $\text{(R)-1}\text{.6-dimethylcyclohexane}$ is treated with ${\text{CH}}_{\text{2}}{\text{N}}_{\text{2}}$ and irradiated with ultraviolet light is

Explanation of Solution

Diazomethane dissociates heterolytically when irradiated with ultraviolet light to produce a carbene and a nitrogen molecule.

The carbene then simultaneously adds to the initially double-bonded carbons. The lone pair on the carbene forms a bond with one carbon while the $\text{π}$ bond pair from the double bond forms a bond with the carbon from the carbene. This produces a cyclopropane ring.

Since the starting alkene is chiral, the product will be a mixture of two enantiomers. The pair of enantiomers is produced because the carbene can add either above or below the plane of the ring in the reactant.

Thus the complete mechanism for this reaction can be drawn as

Conclusion

A carbene adds to an alkene or alkyne to produce a cyclopropane ring.

Interpretation Introduction

(b)

Interpretation:

The mechanism for the reaction that will take place when the given compound is treated with ${\text{CH}}_{\text{2}}{\text{N}}_{\text{2}}$ and irradiated with ultraviolet light is to be drawn.

Concept introduction:

Diazomethane, ${\text{CH}}_{\text{2}}{\text{N}}_{\text{2}}$, dissociates heterolytically into a carbene and a nitrogen molecule when irradiated with ultraviolet light. The carbene adds to the double bond, simultaneously forming bonds to both carbons of the double bond. This results in the formation of a cyclopropane ring.

The stereochemistry of the double bond is preserved in the addition. If the double bond has a cis relationship, then the two substituents end up on the same side of the cyclopropane ring. If the two substituents on the double bond are trans to each other, they end up on the opposite sides of the cyclopropane ring. This also determines the product distribution if the cyclic product is chiral. If the starting alkene is achiral and the product chiral, the product is a racemic mixture of enantiomers. If the starting alkene is also chiral, then an unequal mixture of enantiomers is produced.

Answer to Problem 12.26P

The mechanism for the given reaction is

Explanation of Solution

Diazomethane dissociates heterolytically when irradiated with ultraviolet light to produce a carbene and a nitrogen molecule.

The carbene then simultaneously adds to the initially double-bonded carbons. The lone pair on the carbene forms a bond with one carbon while the $\text{π}$ bond pair from the double bond forms a bond with the carbon from the carbene. This produces a cyclopropane ring.

The carbene then simultaneously adds to the initially double-bonded carbons. The lone pair on the carbene forms a bond with one carbon while the $\text{π}$ bond pair from the double bond forms a bond with the carbon from the carbene. This produces a cyclopropane ring.

Since the starting alkene is chiral, the product will be a mixture of two enantiomers. The pair of enantiomers is produced because the carbene can add either above or below the plane of the ring in the reactant.

Thus the complete mechanism for this reaction can be drawn as:

Conclusion

A carbene adds to an alkene or alkyne to produce a cyclopropane ring.

Interpretation Introduction

(c)

Interpretation:

The mechanism for the reaction that will take place when the given compound is treated with ${\text{CH}}_{\text{2}}{\text{N}}_{\text{2}}$ and irradiated with ultraviolet light is to be drawn.

Concept introduction:

Diazomethane, ${\text{CH}}_{\text{2}}{\text{N}}_{\text{2}}$, dissociates heterolytically into a carbene and a nitrogen molecule when irradiated with ultraviolet light. The carbene adds to the double bond, simultaneously forming bonds to both carbons of the double bond. This results in the formation of a cyclopropane ring.

The stereochemistry of the double bond is preserved in the addition. If the double bond has a cis relationship, then the two substituents end up on the same side of the cyclopropane ring. If the two substituents on the double bond are trans to each other, they end up on the opposite sides of the cyclopropane ring. This also determines the product distribution if the cyclic product is chiral. If the starting alkene is achiral and the product chiral, the product is a racemic mixture of enantiomers. If the starting alkene is also chiral, then an unequal mixture of enantiomers is produced.

Answer to Problem 12.26P

The mechanism for the given reaction is

Explanation of Solution

Diazomethane dissociates heterolytically when irradiated with ultraviolet light to produce a carbene and a nitrogen molecule.

The carbene then simultaneously adds to the initially double-bonded carbons. The lone pair on the carbene forms a bond with one carbon while the $\text{π}$ bond pair from the double bond forms a bond with the carbon from the carbene. This produces a cyclopropane ring.

Only one product is formed in this case because of the symmetry of the reactant alkene about the axis of the double bond.

Thus, the complete mechanism for the given reaction can be drawn as

Conclusion

A carbene adds to an alkene or alkyne to produce a cyclopropane ring.

Interpretation Introduction

(d)

Interpretation:

The mechanism for the reaction that will take place when the given compound is treated with ${\text{CH}}_{\text{2}}{\text{N}}_{\text{2}}$ and irradiated with ultraviolet light is to be drawn.

Concept introduction:

Diazomethane, ${\text{CH}}_{\text{2}}{\text{N}}_{\text{2}}$, dissociates heterolytically into a carbene and a nitrogen molecule when irradiated with ultraviolet light. The carbene adds to the double bond, simultaneously forming bonds to both carbons of the double bond. This results in the formation of a cyclopropane ring.

The stereochemistry of the double bond is preserved in the addition. If the double bond has a cis relationship, then the two substituents end up on the same side of the cyclopropane ring. If the two substituents on the double bond are trans to each other, they end up on the opposite sides of the cyclopropane ring. This also determines the product distribution if the cyclic product is chiral. If the starting alkene is achiral and the product chiral, the product is a racemic mixture of enantiomers. If the starting alkene is also chiral, then an unequal mixture of enantiomers is produced.

Answer to Problem 12.26P

The mechanism for the given reaction is

Explanation of Solution

Diazomethane dissociates heterolytically when irradiated with ultraviolet light to produce a carbene and a nitrogen molecule.

The carbene then simultaneously adds to the initially double-bonded carbons. The lone pair on the carbene forms a bond with one carbon while the $\text{π}$ bond pair from the double bond forms a bond with the carbon from the carbene. This produces a cyclopropane ring.

The starting alkene has a trans geometry, therefore, the two substituents on the cyclopropane ring in the product are on opposite sides of the ring.

This means the product is chiral, and a racemic mixture of two enantiomers will be produced.

Thus, the complete mechanism for the reaction can be drawn as

Conclusion

A carbene adds to an alkene or alkyne to produce a cyclopropane ring.

Interpretation Introduction

(e)

Interpretation:

The mechanism for the reaction that will take place when the given compound is treated with ${\text{CH}}_{\text{2}}{\text{N}}_{\text{2}}$ and irradiated with ultraviolet light is to be drawn.

Concept introduction:

Diazomethane, ${\text{CH}}_{\text{2}}{\text{N}}_{\text{2}}$, dissociates heterolytically into a carbene and a nitrogen molecule when irradiated with ultraviolet light. The carbene adds to the double bond, simultaneously forming bonds to both carbons of the double bond. This results in the formation of a cyclopropane ring.

The stereochemistry of the double bond is preserved in the addition. If the double bond has a cis relationship, then the two substituents end up on the same side of the cyclopropane ring. If the two substituents on the double bond are trans to each other, they end up on the opposite sides of the cyclopropane ring. This also determines the product distribution if the cyclic product is chiral. If the starting alkene is achiral and the product chiral, the product is a racemic mixture of enantiomers. If the starting alkene is also chiral, then an unequal mixture of enantiomers is produced.

Answer to Problem 12.26P

The mechanism for the given reaction is

Explanation of Solution

Diazomethane dissociates heterolytically when irradiated with ultraviolet light to produce a carbene and a nitrogen molecule.

The carbene then simultaneously adds to the initially double-bonded carbons. The lone pair on the carbene forms a bond with one carbon while the $\text{π}$ bond pair from the double bond forms a bond with the carbon from the carbene. This produces a cyclopropane ring.

The starting alkene has a cis geometry and is symmetric. Therefore, only one product, a meso compound is produced.

Thus the complete mechanism for this reaction can be drawn as

Conclusion

A carbene adds to an alkene or alkyne to produce a cyclopropane ring.