Chapter 13, Problem 13.35P

Interpretation Introduction

(a)

Interpretation:

An alkyl halide, that can be used to synthesize the given alkene exclusively via an E2 reaction paying attention to stereochemistry, is to be provided.

Concept introduction:

E2 stands for bimolecular elimination. This reaction is a one-step concerted mechanism. In this step, the C-X and C-H bond breaks to form a double bond. The leaving group and the adjacent hydrogen atom must be anticoplanar in the precursor for the E2 step to be favored. To arrive back at the alkyl halide, one must add hydrogen and a halogen on the alkene carbons in an anti-fashion.

Since the alkyl halide and base influence the rate of reaction, this is a bimolecular reaction. A strong base is used to form the most substituted alkene as the major product.

Answer to Problem 13.35P

An alkyl halide that could have been used to synthesize the known alkene exclusively via an E2 reaction paying attention to stereochemistry is:

Explanation of Solution

The structure of the desired alkene is:

The given alkene has both the higher priority groups attached on the opposite side of the double bond. Hence, the stereochemistry is E. Alkenes can be prepared from corresponding alkyl halides via E2 reactions. This reaction is a one-step concerted mechanism. In this step, the C-X and C-H bond breaks to form a double bond. The leaving group and the adjacent hydrogen atom must be anticoplanar in the precursor for the E2 step to be favored. To arrive back at the alkyl halide, one must add hydrogen and a halogen on the alkene carbons in an anti-fashion. Thus, the original alkyl halide that could have been used to prepare the given alkene must be:

Conclusion

To arrive back at the alkyl halide, one must add hydrogen and a halogen on the alkene carbons in an anti-fashion.

Interpretation Introduction

(b)

Interpretation:

An alkyl halide, that can be used to synthesize the given alkene exclusively via an E2 reaction paying attention to stereochemistry, is to be provided.

Concept introduction:

The name E2 represents bimolecular elimination. This reaction is a one-step concerted mechanism. In this step, the C-X and C-H bond breaks to form a double bond. The leaving group and the adjacent hydrogen atom must be anticoplanar in the precursor for the E2 step to be favored. To arrive back at the alkyl halide, one must add hydrogen and a halogen on the alkene carbons in an anti-fashion.

Since the alkyl halide and base influence the rate of reaction, this is a bimolecular reaction. A strong base is used to form the most substituted alkene as the major product.

Answer to Problem 13.35P

An alkyl halide that could have been used to prepare the given alkene exclusively via an E2 reaction paying attention to stereochemistry is:

Explanation of Solution

The structure of the required alkene is:

The given alkene has both the most priority groups attached on the same side of the double bond. Therefore, the stereochemistry about the double bond is Z. Alkenes can be prepared from corresponding alkyl halides via E2 reactions. This reaction is a one-step concerted mechanism. In this step, the C-X and C-H bond breaks to form a double bond. The leaving group and the adjacent hydrogen atom must be anticoplanar in the precursor for the E2 step to be favored. To arrive back at the alkyl halide, one must add hydrogen and a halogen on the alkene carbons in an anti-fashion. Thus, the original alkyl halide that could have been used to prepare the given alkene must be:

Conclusion

To arrive back at the alkyl halide, one must add hydrogen and a halogen on the alkene carbons in an anti-fashion.

Interpretation Introduction

(c)

Interpretation:

An alkyl halide, that can be used to synthesize the given alkene exclusively via an E2 reaction paying attention to stereochemistry, is to be provided.

Concept introduction:

The name E2 represents bimolecular elimination. This reaction is a one-step concerted mechanism. In this step, the C-X and C-H bond breaks to form a double bond. The leaving group and the adjacent hydrogen atom must be anticoplanar in the precursor for the E2 step to be favored. To arrive back at the alkyl halide, one must add hydrogen and a halogen on the alkene carbons in an anti-fashion.

Since the alkyl halide and base influence the rate of reaction, this is a bimolecular reaction. A strong base is used to form the most substituted alkene as the major product.

Answer to Problem 13.35P

An alkyl halide that could have been used to prepare the given alkene exclusively via an E2 reaction paying attention to stereochemistry is:

Explanation of Solution

The structure of the desired alkene is:

The alkene is a cycloalkene having two methyl groups attached to the double-bonded carbon atoms. As the carbon atoms in alkenes are ${\text{sp}}^2$ hybridized, all the atoms must be in the plane. Alkenes can be prepared from corresponding alkyl halides via E2 reactions. This reaction is a one-step concerted mechanism. In this step, the C-X and C-H bond breaks to form a double bond. The leaving group and the adjacent hydrogen atom must be anticoplanar in the precursor for the E2 step to be favored. To arrive back at the alkyl halide, one must add hydrogen and a halogen on the alkene carbons in an anti-fashion. Thus, the original alkyl halide that could have been used to prepare the given alkene must be:

Conclusion

To arrive back at the alkyl halide, one must add hydrogen and a halogen on the alkene carbons in an anti-fashion.

Interpretation Introduction

(d)

Interpretation:

An alkyl halide, that can be used to synthesize the given alkene exclusively via an E2 reaction paying attention to stereochemistry, is to be provided.

Concept introduction:

The name E2 represents bimolecular elimination. This reaction is a one-step concerted mechanism. In this step, the C-X and C-H bond breaks to form a double bond. The leaving group and the adjacent hydrogen atom must be anticoplanar in the precursor for the E2 step to be favored. To arrive back at the alkyl halide, one must add hydrogen and a halogen on the alkene carbons in an anti-fashion.

Since the alkyl halide and base influence the rate of reaction, this is a bimolecular reaction. A strong base is used to form the most substituted alkene as the major product.

Answer to Problem 13.35P

An alkyl halide that could have been used to prepare the given alkene exclusively via an E2 reaction paying attention to stereochemistry is:

Explanation of Solution

The structure of the desired alkene is:

The alkene is cyclohexene having three methyl groups as substituents.

As the carbon atoms in alkenes are sp2 hybridized, all the atoms that are directly attached to the double-bonded carbon atoms must be in the plane. There are two chiral centers in the molecule at C3 and C6 carbon atoms. The stereochemistry for those two chiral centers will not change and will be retained as the reaction does not occur at those two chiral centers. Alkenes can be prepared from corresponding alkyl halides via E2 reactions.

This reaction is a one-step concerted mechanism. In this step, the C-X and C-H bond breaks to form a double bond. The leaving group and the adjacent hydrogen atom must be anticoplanar in the precursor for the E2 step to be favored. To arrive back at the alkyl halide, one must add hydrogen and a halogen on the alkene carbons in an anti-fashion. Thus, the original alkyl halide that could have been used to prepare the given alkene must be:

Conclusion

To arrive back at the alkyl halide, one must add hydrogen and a halogen on the alkene carbons in an anti-fashion.

Interpretation Introduction

(e)

Interpretation:

An alkyl halide, that can be used to synthesize the given alkene exclusively via an E2 reaction paying attention to stereochemistry, is to be provided.

Concept introduction:

The name E2 represents bimolecular elimination. This reaction is a one-step concerted mechanism. In this step, the C-X and C-H bond breaks to form a double bond. The leaving group and the adjacent hydrogen atom must be anticoplanar in the precursor for the E2 step to be favored. To arrive back at the alkyl halide, one must add hydrogen and a halogen on the alkene carbons in an anti-fashion.

Since the alkyl halide and base influence the rate of reaction, this is a bimolecular reaction. A strong base is used to form the most substituted alkene as the major product.

Answer to Problem 13.35P

An alkyl halide that could have been used to prepare the given alkene exclusively via an E2 reaction paying attention to stereochemistry is:

Explanation of Solution

The structure of the desired alkene is:

The alkene is cyclohexene having three methyl groups as substituents.

As the carbon atoms in alkenes are sp2 hybridized, all the atoms that are directly attached to the double-bonded carbon atoms must be in the plane. There are two chiral centers in the molecule at C3 and C6 carbon atoms. The stereochemistry for those two chiral centers will not change and will be retained as the reaction does not occur at those two chiral centers. Alkenes can be prepared from corresponding alkyl halides via E2 reactions.

This reaction involves a one-step mechanism (concerted) in which carbon-halogen bond and carbon-hydrogen bond breaks to form a double bond. The leaving group and the adjacent hydrogen atom must be anticoplanar in the precursor for the E2 step to be favored. To arrive back at the alkyl halide, one must add hydrogen and a halogen on the alkene carbons in an anti-fashion. Thus, the original alkyl halide that could have been used to synthesize the given alkene must be:

Conclusion

To arrive back at the alkyl halide, one must add hydrogen and a halogen on the alkene carbons in an anti-fashion.