Question

Draw the major, neutral organic product obtained if: the reaction proceeds by the SN1 mechanism the reaction proceeds by the SN2 mechanism. Draw the major, neutral organic product for each substitution reaction below. (For this question, assume that each substitution reaction goes to completion. Disregard elimination.)

Answer 1

General guidance

Concepts and reason

The problem is based on the concept of nucleophilic substitution reaction. There are two mechanisms for nucleophilic substitution that is${S_{\\rm{N}}}1$ and ${S_{\\rm{N}}}2$. Nucleophilic ${S_{\\rm{N}}}1$ reaction is a nucleophilic substitution in a unimolecular mechanism. It is favored in presence of weak bases or poor nucleophile and ${S_{\\rm{N}}}2$reaction is a nucleophilic substitution in a bimolecular mechanism.

Fundamentals

The [{S_{ m{N}}}1] reaction follows a 2 step mechanism. General reaction is as follows:

The [{S_{ m{N}}}2] reaction follows a single step mechanism which is shown below:

+Nu Br --Br Nu Nu-- Br

Step-by-step

Step 1 of 5

Part 1.a

If reaction proceeds via ${S_{\\rm{N}}}1$mechanism, Carbocation formation takes place followed by rearrangement for more stable Carbocation. After the formation of Carbocation, substitution of nucleophile takes place on carbon bearing positive charge. This is represented as follows:

Mechanism for ${S_{\\rm{N}}}1$reaction:

Part 1.a

The major neutral product if reaction proceeds via ${S_{\\rm{N}}}1$ mechanism:

H\u1ecc SN2

Explanation | Common mistakes | Hint for next step

Following the mechanism, in the first step a Carbocation is formed which undergoes rearrangement as tertiary Carbocation is most stable Carbocation. In the second step, substitution of nucleophile takes place.

Step 2 of 5

Part 1.b

Attack of nucleophile via [{S_{ m{N}}}2] mechanism is as follows:

Br SNI +OH 1,3-H shift -Br +OH

Part 1.b

The major neutral product if reaction proceeds via [{S_{ m{N}}}2] mechanism:

Br OH SN2

Explanation | Common mistakes | Hint for next step

Following the given mechanism, addition of the nucleophile occurs and removal of the halide ion takes place in single step.

Step 3 of 5

Part 2.a

If reaction proceeds via [{S_{ m{N}}}1]mechanism, Carbocation formation takes place followed by rearrangement for more stable Carbocation. After the formation of Carbocation, substitution of nucleophile takes place on carbon bearing positive charge. This is represented as follows:

Mechanism for [{S_{ m{N}}}1]reaction:

H20 weak base SN1 \u043e\u043d CI OH strong base SN2 HQ

Part 2.a

The major neutral product if reaction proceeds via [{S_{ m{N}}}1] mechanism:

Explanation | Common mistakes | Hint for next step

Following the mechanism, in the first step a Carbocation is formed which undergoes rearrangement as tertiary Carbocation is most stable Carbocation. In the second step, substitution of nucleophile takes place.

Step 4 of 5

Part 2.b

Attack of nucleophile via [{S_{ m{N}}}2] mechanism is as follows:

Part 2.b

The major neutral product if reaction proceeds via [{S_{ m{N}}}2] mechanism:

\u043e\u043d

Explanation | Common mistakes | Hint for next step

Following the given mechanism, addition of the nucleophile occurs and removal of the halide ion takes place in single step.

Step 5 of 5

Part 3

Water, [{{ m{H}}_{ m{2}}}{ m{O}}]is a weak base in comparison to hydroxide ion. As a result, [{S_{ m{N}}}1] reaction occurs with [{{ m{H}}_{ m{2}}}{ m{O}}] and [{S_{ m{N}}}2] with hydroxide ion,[{ m{O}}{{ m{H}}^ - }] which is strong base. Therefore, the products formed are:

HO

[Part 3]

Part 3

Part 3

Products formed are as follows:

H\u1ecc

Upon identifying the kind of reaction mechanism that will occur based on strength of the base, addition of the nucleophile occurs and removal of the halide ion. In the reaction that follows ${S_{\\rm{N}}}1$mechanism, there is 1,2-hydride shift take place in order to form more stable Carbocation. In ${S_{\\rm{N}}}2$ mechanism, there is no rearrangement attack of nucleophile take place on same position from where leaving group leaves.

Answer

Part 1.a

The major neutral product if reaction proceeds via ${S_{\\rm{N}}}1$ mechanism:

H\u1ecc

Part 1.b

The major neutral product if reaction proceeds via [{S_{ m{N}}}2] mechanism:

H\u1ecc

Part 2.a

The major neutral product if reaction proceeds via [{S_{ m{N}}}1] mechanism:

HO

Part 2.b

The major neutral product if reaction proceeds via [{S_{ m{N}}}2] mechanism:

\u043e\u043d

Part 3

Products formed are as follows:

Answer only

Part 1.a

The major neutral product if reaction proceeds via ${S_{\\rm{N}}}1$ mechanism:

H\u1ecc

Part 1.b

The major neutral product if reaction proceeds via [{S_{ m{N}}}2] mechanism:

H\u1ecc

Part 2.a

The major neutral product if reaction proceeds via [{S_{ m{N}}}1] mechanism:

HO

Part 2.b

The major neutral product if reaction proceeds via [{S_{ m{N}}}2] mechanism:

\u043e\u043d

Part 3

Products formed are as follows: