Chapter 7, Problem 7.36P

Interpretation Introduction

(a)

Interpretation:

The curved arrow notations showing all possible $\text{1, 2-hydride shifts}$ and all possible $\text{1, 2-methyl shifts}$ and the corresponding products are to be shown for the given carbocation.

Concept introduction:

Curved arrows are used to represent the movement of electrons in a reaction mechanism. The arrow starts on an electron-rich atom or an electron-rich region such as a pi bond. It ends on an electron poor atom when the movement results in the formation of a new sigma bond. If the result is the formation of a pi bond, the arrow ends in the region between the two atoms that form the bond.

A carbocation is a positively charged carbon atom that is electron-poor, two electrons short of an octet. It is unstable because it is a charged species.

A $\text{1, 2-hydride shift}$ involves the migration of a hydrogen atom along with its bonding electrons on a carbon adjacent to a carbocation to the carbon with the positive charge. The carbocation is a highly unstable electron poor carbon with a 1+ charge and an incomplete octet. The $\text{C}-\text{H}$ bond on the adjacent carbon is a relatively electron-rich region and can migrate to the electron-poor carbocation.

A $\text{1, 2-methyl shift}$ is similar, the only difference being that the methyl group $-{\text{CH}}_3$ migrates with its pair of bonding electrons instead of the hydrogen atom.

The numbering in the shift label simply signifies that a hydride or a methyl group migrates from one carbon to an adjacent one. The numbering is not related to the root chain atom numbering.

Answer to Problem 7.36P

The possible $\text{1, 2-hydride shifts}$ and $\text{1, 2-methyl shifts}$ in the given carbocation are

Explanation of Solution

The structure of the carbocation is

The charge is on the carbon numbered 1. There are two hydrogen atoms on the adjacent carbons C2 and C3. These are the ones that can shift to C1 in the two possible $\text{1, 2-hydride shifts}$. Therefore, the $\text{1, 2-hydride shifts}$ can be shown using curved arrows, as shown in the figure below. Shifting the hydride from C2 results in the charge shifting to C2, as shown in the product on the right. Shifting of the hydride from C3 to C1 results in the charge shifting to C3, as shown in the product on the left.

There is only one methyl group on the carbon adjacent to C1, attached to C2. Shifting of this methyl to C1 results in shifting of the charge to C2. Therefore, the $\text{1, 2-methyl shift}$ can be shown as follows:

Conclusion

A hydride (${\text{H}}^{-}$) or a methyl ($-{\text{CH}}_3{}^{-}$) group on a carbon adjacent to a carbocation can shift to the positively charged carbon atom, along with its bonding electrons in a process called $\text{1, 2-hydride shift}$ or $\text{1, 2-methyl shift}$ respectively.

Interpretation Introduction

(b)

Interpretation:

The curved arrow notations showing all possible $\text{1, 2-hydride shifts}$ and all possible $\text{1, 2-methyl shifts}$ and the corresponding products are to be shown for the given carbocation.

Concept introduction:

Curved arrows are used to represent the movement of electrons in a reaction mechanism. The arrow starts on an electron-rich atom or an electron-rich region such as a pi bond. It ends on an electron poor atom when the movement results in the formation of a new sigma bond. If the result is the formation of a pi bond, the arrow ends in the region between the two atoms that form the bond.

A carbocation is a positively charged carbon atom that is electron-poor, two electrons short of an octet. It is unstable because it is a charged species.

A $\text{1, 2-hydride shift}$ involves the migration of a hydrogen atom along with its bonding electrons on a carbon adjacent to a carbocation to the carbon with the positive charge. The carbocation is a highly unstable electron poor carbon with a 1+ charge and an incomplete octet. The $\text{C}-\text{H}$ bond on the adjacent carbon is a relatively electron-rich region and can migrate to the electron-poor carbocation.

A $\text{1, 2-methyl shift}$ is similar, the only difference being that the methyl group $-{\text{CH}}_3$ migrates with its pair of bonding electrons instead of the hydrogen atom.

The numbering in the shift label simply signifies that a hydride or a methyl group migrates from one carbon to an adjacent one. The numbering is not related to the root chain atom numbering.

Answer to Problem 7.36P

The possible $\text{1, 2-hydride shifts}$ and $\text{1, 2-methyl shifts}$ in the given carbocation are

Explanation of Solution

The structure of the given carbocation is

There are two hydrogen atoms on adjacent carbons C2 and C3 that can shift to the positively charged carbon C1 in two possible $\text{1, 2-hydride shifts}$. Shifting of the hydride from C2 results in the charge shifting to C2 as shown in the product on the right. Shifting of the hydride on C3 results in the charge shifting to C3, as shown in the product on the left. Therefore, the two $\text{1, 2-hydride shifts}$ can be shown as

There are two methyl groups attached to a carbon adjacent to C1. Both are on the same carbon C3, therefore, shifting of either one will give the same product.

Therefore, the $\text{1, 2-methyl shift}$ can be shown as

Conclusion

A hydride (${\text{H}}^{-}$) or a methyl ($-{\text{CH}}_3{}^{-}$) group on a carbon adjacent to a carbocation can shift to the positively charged carbon atom, along with its bonding electrons in a process called $\text{1, 2-hydride shift}$ or $\text{1, 2-methyl shift}$ respectively.

Interpretation Introduction

(c)

Interpretation:

The curved arrow notations showing all possible $\text{1, 2-hydride shifts}$ and all possible $\text{1, 2-methyl shifts}$ and the corresponding products are to be shown for the given carbocation.

Concept introduction:

Curved arrows are used to represent the movement of electrons in a reaction mechanism. The arrow starts on an electron-rich atom or an electron-rich region such as a pi bond. It ends on an electron poor atom when the movement results in the formation of a new sigma bond. If the result is the formation of a pi bond, the arrow ends in the region between the two atoms that form the bond.

A carbocation is a positively charged carbon atom that is electron-poor, two electrons short of an octet. It is unstable because it is a charged species.

A $\text{1, 2-hydride shift}$ involves the migration of a hydrogen atom along with its bonding electrons on a carbon adjacent to a carbocation to the carbon with the positive charge. The carbocation is a highly unstable electron poor carbon with a 1+ charge and an incomplete octet. The $\text{C}-\text{H}$ bond on the adjacent carbon is a relatively electron-rich region and can migrate to the electron-poor carbocation.

A $\text{1, 2-methyl shift}$ is similar, the only difference being that the methyl group $-{\text{CH}}_3$ migrates with its pair of bonding electrons instead of the hydrogen atom.

The numbering in the shift label simply signifies that a hydride or a methyl group migrates from one carbon to an adjacent one. The numbering is not related to the root chain atom numbering.

Answer to Problem 7.36P

The possible $\text{1, 2-hydride shifts}$ and $\text{1, 2-methyl shifts}$ in the given carbocation are

Explanation of Solution

The structure of the given carbocation is

There are two hydrogen atoms on adjacent carbons C2 and C3 that can shift to the positively charged carbon C1 in two possible $\text{1, 2-hydride shifts}$. Shifting of the hydride from C2 results in the charge shifting to C2, as shown in the product on the right. Shifting of the hydride on C3 results in the charge shifting to C3, as shown in the product on the left. Therefore, the two $\text{1, 2-hydride shifts}$ can be shown as

There are two methyl groups attached to a carbon adjacent to C1. Both are on the same carbon C3; therefore, shifting of either one will give the same product.

Therefore, the $\text{1, 2-methyl shift}$ can be shown as follows:

Conclusion

A hydride (${\text{H}}^{-}$) or a methyl ($-{\text{CH}}_3{}^{-}$) group on a carbon adjacent to a carbocation can shift to the positively charged carbon atom along with its bonding electrons in a process called $\text{1, 2-hydride shift}$ or $\text{1, 2-methyl shift}$ respectively.

Interpretation Introduction

(d)

Interpretation:

The curved arrow notations showing all possible $\text{1, 2-hydride shifts}$ and all possible $\text{1, 2-methyl shifts}$ and the corresponding products are to be shown for the given carbocation.

Concept introduction:

Curved arrows are used to represent the movement of electrons in a reaction mechanism. The arrow starts on an electron-rich atom or an electron-rich region such as a pi bond. It ends on an electron poor atom when the movement results in the formation of a new sigma bond. If the result is the formation of a pi bond, the arrow ends in the region between the two atoms that form the bond.

A carbocation is a positively charged carbon atom that is electron-poor, two electrons short of an octet. It is unstable because it is a charged species.

A $\text{1, 2-hydride shift}$ involves the migration of a hydrogen atom along with its bonding electrons on a carbon adjacent to a carbocation to the carbon with the positive charge. The carbocation is a highly unstable electron poor carbon with a 1+ charge and an incomplete octet. The $\text{C}-\text{H}$ bond on the adjacent carbon is a relatively electron-rich region and can migrate to the electron-poor carbocation.

A $\text{1, 2-methyl shift}$ is similar, the only difference being that the methyl group $-{\text{CH}}_3$ migrates with its pair of bonding electrons instead of the hydrogen atom.

The numbering in the shift label simply signifies that a hydride or a methyl group migrates from one carbon to an adjacent one. The numbering is not related to the root chain atom numbering.

Answer to Problem 7.36P

The possible $\text{1, 2-hydride shift}$ in the given carbocation is

As there are no methyl groups on the carbon adjacent to the charge bearing carbon C1, a $\text{1, 2-methyl shift}$ is not possible in this carbocation.

Explanation of Solution

The structure of the given carbocation is

There is only one hydrogen atom on an adjacent carbon, C2, that can shift to the positively charged carbon C1 in a possible $\text{1, 2-hydride shift}$. Shifting of the hydride from C2 results in the charge shifting to C2, as shown in the product on the right.

Therefore, the $\text{1, 2-hydride shift}$ can be shown as

There are no methyl groups attached to the carbon adjacent to C1. Therefore, a $\text{1, 2-methyl shift}$ is not possible in this carbocation.

Conclusion

A hydride (${\text{H}}^{-}$) or a methyl ($-{\text{CH}}_3{}^{-}$) group on a carbon adjacent to a carbocation can shift to the positively charged carbon atom along with its bonding electrons in a process called $\text{1, 2-hydride shift}$ or $\text{1, 2-methyl shift}$ respectively.

Interpretation Introduction

(e)

Interpretation:

The curved arrow notations showing all possible $\text{1, 2-hydride shifts}$ and all possible $\text{1, 2-methyl shifts}$ and the corresponding products are to be shown for the given carbocation.

Concept introduction:

Curved arrows are used to represent the movement of electrons in a reaction mechanism. The arrow starts on an electron-rich atom or an electron-rich region such as a pi bond. It ends on an electron poor atom when the movement results in the formation of a new sigma bond. If the result is the formation of a pi bond, the arrow ends in the region between the two atoms that form the bond.

A carbocation is a positively charged carbon atom that is electron-poor, two electrons short of an octet. It is unstable because it is a charged species.

A $\text{1, 2-hydride shift}$ involves the migration of a hydrogen atom along with its bonding electrons on a carbon adjacent to a carbocation to the carbon with the positive charge. The carbocation is a highly unstable electron poor carbon with a 1+ charge and an incomplete octet. The $\text{C}-\text{H}$ bond on the adjacent carbon is a relatively electron-rich region and can migrate to the electron-poor carbocation.

A $\text{1, 2-methyl shift}$ is similar, the only difference being that the methyl group $-{\text{CH}}_3$ migrates with its pair of bonding electrons instead of the hydrogen atom.

The numbering in the shift label simply signifies that a hydride or a methyl group migrates from one carbon to an adjacent one. The numbering is not related to the root chain atom numbering.

Answer to Problem 7.36P

The possible $\text{1, 2-hydride shifts}$ and $\text{1, 2-methyl shifts}$ in the given carbocation are

Explanation of Solution

The structure of the given carbocation is

There are three hydrogen atoms on carbon atoms adjacent to the charge carrying carbon. They are on C2, C3, and C4.

Shifting of the hydride on C2 results in the charge shifting to C2, as shown in the product on the right.

Shifting of the hydride on C3 results in the charge shifting to C3, as shown in the product on the left.

Shifting of the hydride on C4 results in the charge shifting to C4, as shown in the product below the given carbocation.

Therefore, the $\text{1, 2-hydride shifts}$ can be shown as

There is one methyl group attached to the carbon adjacent to C1. Shifting of the methyl group on C2 to C1 results in C1 becoming a tertiary carbon and the charge shifting to C2.

Therefore, the possible $\text{1, 2-methyl shift}$ can be shown as follows:

Conclusion

A hydride (${\text{H}}^{-}$) or a methyl ($-{\text{CH}}_3{}^{-}$) group on a carbon adjacent to a carbocation can shift to the positively charged carbon atom along with its bonding electrons in a process called $\text{1, 2-hydride shift}$ or $\text{1, 2-methyl shift}$ respectively.

Interpretation Introduction

(f)

Interpretation:

The curved arrow notations showing all possible $\text{1, 2-hydride shifts}$ and all possible $\text{1, 2-methyl shifts}$ and the corresponding products are to be shown for the given carbocation.

Concept introduction:

Curved arrows are used to represent the movement of electrons in a reaction mechanism. The arrow starts on an electron-rich atom or an electron-rich region such as a pi bond. It ends on an electron poor atom when the movement results in the formation of a new sigma bond. If the result is the formation of a pi bond, the arrow ends in the region between the two atoms that form the bond.

A carbocation is a positively charged carbon atom that is electron-poor, two electrons short of an octet. It is unstable because it is a charged species.

A $\text{1, 2-hydride shift}$ involves the migration of a hydrogen atom along with its bonding electrons on a carbon adjacent to a carbocation to the carbon with the positive charge. The carbocation is a highly unstable electron poor carbon with a 1+ charge and an incomplete octet. The $\text{C}-\text{H}$ bond on the adjacent carbon is a relatively electron-rich region and can migrate to the electron-poor carbocation.

A $\text{1, 2-methyl shift}$ is similar, the only difference being that the methyl group $-{\text{CH}}_3$ migrates with its pair of bonding electrons instead of the hydrogen atom.

The numbering in the shift label simply signifies that a hydride or a methyl group migrates from one carbon to an adjacent one. The numbering is not related to the root chain atom numbering.

Answer to Problem 7.36P

The possible $\text{1, 2-hydride shifts}$ and $\text{1, 2-methyl shifts}$ in the given carbocation are

Explanation of Solution

The structure of the given carbocation is

There are three hydrogen atoms on carbon atoms adjacent to the charge carrying carbon. They are on C2, C3, and C4.

Shifting of the hydride on C2 results in the charge shifting to C2, as shown in the product on the right.

Shifting of the hydride on C3 results in the charge shifting to C3, as shown in the product on the left.

Shifting of the hydride on C4 results in the charge shifting to C4, as shown in the product below the given carbocation.

Therefore, the $\text{1, 2-hydride shifts}$ can be shown as

There is one methyl group attached to a carbon adjacent to C1. Shifting of the methyl group on C2 to C1 results in C1 becoming a tertiary carbon and the charge shifting to C2.

Therefore, the possible $\text{1, 2-methyl shift}$ can be shown as follows:

Conclusion

A hydride (${\text{H}}^{-}$) or a methyl ($-{\text{CH}}_3{}^{-}$) group on a carbon adjacent to a carbocation can shift to the positively charged carbon atom, along with its bonding electrons in a process called $\text{1, 2-hydride shift}$ or $\text{1, 2-methyl shift}$ respectively.