Chapter 10, Problem 10.1P

Interpretation Introduction

(a)

Interpretation:

The complete and detailed mechanism is to be drawn for the given reaction.

Concept introduction:

The S_N1 is an abbreviation for unimolecular nucleophilic substitution reaction. These reactions are two-step reactions. The first step is the formation of carbocation intermediate, followed by the nucleophilic attack, which is a second step. Due to the formation of a planar carbocation, the incoming nucleophile can attack the carbocation from two sides, either from the front of the plane or from the back side of the plane.

This leads to give the mixture of stereoisomers. When secondary and tertiary alcohols are treated with strong concentrated acids, it follows SN1 and E1 mechanism.

Answer to Problem 10.1P

The complete and detailed mechanism for given reaction is as follows:

Explanation of Solution

The given reaction is as follows:

The hydroxyl ($\text{-OH}$) group in the given substrate is a leaving group and can be protonated using concentrated strong acid, which converts it into a good leaving group.

The departure of water is a slow step that leads to formation of carbocation, and thus it is the rate-determining step. Due to the formation of planar carbocation intermediate, the incoming nucleophile can attack from either sides, either the top (from above the plane) or bottom (from below of plane). The bromide ion formed in the proton transfer step is the attacking species in the second step of the mechanism. In the second step, the bromide ion (${\text{Br}}^{\text{-}}$) attacks the planar carbocation to form a mixture of stereoisomers.

Both top and bottom attack of nucleophile are possible leads to formation of the mixture of isomers, as shown below:

Conclusion

Due to the formation of carbocation intermediate in S_N1 reaction, a mixture of stereoisomer is produced.

Interpretation Introduction

(b)

Interpretation:

The complete and detailed mechanism is to be drawn for the given reaction.

Concept introduction:

The S_N1 is an abbreviation for unimolecular nucleophilic substitution reaction. These reactions are two-step reactions. The first step is the formation of carbocation intermediate, followed by the nucleophilic attack of attacking species, which is a second step. Due to the formation of a planar carbocation, the incoming nucleophile can attack the carbocation from two sides, either from the front of the plane or from the back side of the plane.

This leads to give the mixture of stereoisomers. When secondary and tertiary alcohols are treated with strong concentrated acids, it follows SN1 and E1 mechanism.

Answer to Problem 10.1P

The complete and detailed mechanism for given reaction is as follows:

Explanation of Solution

The given reaction is as follows:

The hydroxyl ($\text{-OH}$) group in the given substrate is not a good leaving group. But it can be converted into a good leaving group by treating it with a concentrated strong acid. Thus, the first step of the mechanism should be a proton transfer reaction which protonates the $\text{-OH}$ group and converts it into ${\text{H}}_{\text{2}}{\text{O}}^{\text{+}}$ (water molecule), which is an excellent leaving group. The departure of water is a slow step, which leads to the formation of carbocation intermediate. The carbocation intermediate is ${\text{sp}}^2$ hybridized and has a planar geometry. The planar geometry of the resulting carbocation intermediate enables the attack of the nucleophile from either sides of the plane. The incoming nucleophile can attack either from the top (from above the plane) or bottom (from below of plane) of the plane. The bromide ion formed in the proton transfer step is the attacking species in the second step of the mechanism. In the second step, bromide ion (${\text{Br}}^{\text{-}}$) attacks the planar carbocation to form a mixture of stereoisomers.

Both top and bottom attack of nucleophile are possible leads to formation of the mixture of isomers, as shown below:

Conclusion

Due to the formation of carbocation intermediate in S_N1 reaction, a mixture of stereoisomer is produced.