Question

\(\stackrel{\mathrm{nBuLi}}{\longrightarrow} \mathrm{X}+\mathrm{Y} \stackrel{\mathrm{Cl}-\mathrm{CH}_{2} \mathrm{OCH}_{3}}{\longrightarrow}\) COCc1ccccc1 (product) In the above reaction which of the following are incorrect. (1) step-1 is an acid-base reaction (2) step-2 is an \(\mathrm{SN}^{2}\) reaction (3) \(X=n\)-Butane ; \(Y=\) aromatic compound (4) the nucleophile in \(2^{\text {nd }}\) reaction is : \(\mathrm{Bu}^{\Theta}\)

Short answer

Statements 1, 3, and 4 are incorrect.

Step-by-step solution

Understanding the Reaction

The given reaction sequence involves two steps. In the first step, n-BuLi reacts with a compound to give products X and Y. In the second step, X and Y react with Cl-CH2OCH3. We need to identify the type of reactions and the products involved.

Analyze Step-1

n-BuLi is a strong base and a nucleophile. It typically undergoes an acid-base reaction or a nucleophilic addition. In this case, it's highly unlikely that n-BuLi will simply form n-butane (non-reactive product) and an aromatic compound directly by an acid-base mechanism.

Identify Step-2

The second step involves the reaction of X and Y with Cl-CH2OCH3, which suggests a nucleophilic substitution reaction, specifically an \(\text{S}_N^2\) mechanism due to the nature of the reactants (primary alkyl chloride) and conditions.

Correct Incorrect Statements

(1) This step is not predominantly an acid-base reaction because n-BuLi is expected to act as a nucleophile. Hence, statement 1 is incorrect. (2) Since Step-2 is indeed an \(\text{S}_N^2\) reaction, statement 2 is correct. (3) X = n-butane and Y = aromatic compound does not align well with the mechanisms described; hence, statement 3 is incorrect. (4) The nucleophile in the second step is not \(\text{Bu}^{-}\), it is the organolithium derived intermediate from step-1. Hence, statement 4 is incorrect.

Key concepts

Nucleophilic Substitution

Nucleophilic substitution is a fundamental type of reaction in organic chemistry where a nucleophile replaces a leaving group attached to a carbon atom. It commonly occurs in two main mechanisms, namely, \(S_N^1\) and \(S_N^2\). In an \(S_N^2\) reaction, the nucleophile attacks the carbon from the opposite side of the leaving group, forming a transition state where both the leaving group and nucleophile are partially bonded to the carbon.
This type of substitution is stereospecific and often results in the inversion of configuration at the carbon center.
Key characteristics of nucleophilic substitution:

• A strong nucleophile is typically required for \(S_N^2\) reactions.
• The leaving group must be a group that can stabilize the negative charge well upon departure.
• Primary alkyl halides are more likely to undergo \(S_N^2\) mechanisms due to less steric hindrance.

Under these principles, the second step in the exercise involves \(S_N^2\) reaction, where X and Y react with Cl-CH2OCH3. This aligns with the notion that nucleophiles directly attack the electrophilic carbon atom bound to a good leaving group.

Organolithium Reactions

Organolithium compounds are crucial reagents in organic synthesis. They consist of carbon-lithium bonds and exhibit a strong nucleophilic character due to the highly polarized nature of the bond.
In the context of the exercise, n-BuLi (n-Butyllithium) is used as a strong base and nucleophile. Organolithium reagents can undergo a variety of reactions such as:

• Acid-base reactions: Deprotonating acidic hydrogen atoms.
• Carbanion formation: Generating carbanions which can act as nucleophiles in subsequent reactions.
• Nucleophilic addition: Adding across multiple bonds such as carbonyl groups.

In step-1 of the exercise, n-BuLi likely does not form n-butane via an acid-base reaction but rather creates an organolithium intermediate.
Understanding organolithium behavior helps in predicting reaction pathways and intermediates, which are vital for solving complex reaction mechanisms.

Reaction Mechanisms

A reaction mechanism details each step of the bond-breaking and bond-forming processes that lead from reactants to products. These steps are often illustrated using reaction coordinate diagrams showing the progression of the reaction.
Key aspects of studying reaction mechanisms:

• Intermediates: Species that exist within the reaction pathway but are not the final products.
• Transition states: High-energy structures representing the state during bond breaking/forming.
• Reaction steps: Each mini-reaction or transformation within the overall mechanism.

For the exercise provided, the detailed mechanism would include:

• The interaction of n-BuLi with the starting material to form a nucleophilic intermediate.
• The subsequent nucleophilic \(S_N^2\) attack of this intermediate on Cl-CH2OCH3 to yield the final product.

By analyzing each step and considering potential intermediates, students can connect molecular events to the observed products and better understand how reactants are converted through logical steps.