Question

The treatment of \(\mathrm{CH}_{3} \mathrm{Mg} \mathrm{X}\) with \(\mathrm{CH}_{3}-\mathrm{C} \equiv \mathrm{CH}\) produces (1) \(\mathbf{C H}_{4}\) (2) \(\mathrm{CH}_{3} \mathrm{CH}=\mathrm{CH}_{2}\) (3) \(\mathrm{CH}_{3} \mathrm{C} \equiv \mathrm{CCH}_{3}\) (4) \(\mathbf{C H}_{3} \mathrm{CH}=\mathrm{CHCH}_{3}\)

Short answer

(CH₄) methane is produced.

Step-by-step solution

- Understanding the Reactants

We have two reactants here: \(\text{CH}_3\text{MgX}\) and \(\text{CH}_3\text{C} \equiv \text{CH} \). The compound \(\text{CH}_3\text{MgX}\) is a Grignard reagent, which acts as a strong nucleophile and base.

- Identify What Happens on Reaction

Grignard reagents like \(\text{CH}_3\text{MgX}\) readily react with terminal alkynes (compounds with triple bonds at the end). The active site in the alkyne is the hydrogen atom attached to the triple-bonded carbon.

- Formation of Methane (CH₄)

In this reaction, \(\text{CH}_3\text{MgX}\) will deprotonate terminal alkyne \(\text{CH}_3\text{C} \equiv \text{CH}\), producing \(\text{CH}_4\) (methane). The reaction can be described as: \( \text{CH}_3\text{MgX} + \text{CH}_3\text{C} \equiv \text{CH} \rightarrow \text{CH}_4 + \text{CH}_3\text{C} \equiv \text{CMgX} \).

- Product Identification

From the reaction, the primary product generated is \(\text{CH}_4\) (methane). Thus, among the given options, the correct one is \(\text{CH}_4\).

Key concepts

Grignard Reagent

A Grignard reagent is an organomagnesium compound generally represented as \(\text{RMgX}\), where \(\text{R}\) is an alkyl or aryl group, and \(\text{X}\) is a halogen. These reagents are named after the French chemist François Auguste Victor Grignard, who discovered them. Grignard reagents are highly reactive due to the polar bond between the carbon and magnesium atoms. This makes them excellent nucleophiles and strong bases. They are commonly used in organic synthesis to form carbon-carbon bonds.

Deprotonation

Deprotonation is the removal of a proton (hydrogen ion, \(\text{H}^+\)) from a molecule, creating its conjugate base. In the context of Grignard reagents, deprotonation occurs when the Grignard reagent reacts with a molecule containing an acidic hydrogen (like a terminal alkyne). In our given reaction, the Grignard reagent \(\text{CH}_3\text{MgX}\) deprotonates the terminal alkyne \(\text{CH}_3\text{C} \equiv\ \text{CH}\), resulting in the formation of methane (CH₄). The reaction is:
\(\text{CH}_3\text{MgX} + \text{CH}_3\text{C} \equiv\ \text{CH} \rightarrow \text{CH}_4 + \text{CH}_3\text{C} \equiv\ \text{CMgX}\).
This indicates that Grignard reagents can act as strong bases, removing protons from acidic compounds.

Terminal Alkyne

A terminal alkyne is an alkyne (a molecule containing a carbon-carbon triple bond) with the triple bond positioned at the end of the carbon chain, represented by the general formula \(\text{RC} \equiv\ \text{CH}\). The hydrogen atom (attached to the triple-bonded carbon) in terminal alkynes is slightly acidic. This acidity allows the terminal alkyne to undergo deprotonation when treated with a strong base, such as a Grignard reagent. For example, when \(\text{CH}_3\text{C} \equiv\ \text{CH}\) reacts with \(\text{CH}_3\text{MgX}\), the Grignard reagent deprotonates the alkyne, forming methane and a new complex:
\(\text{CH}_3\text{C} \equiv\ \text{CH} + \text{CH}_3\text{MgX} \rightarrow \text{CH}_4 + \text{CH}_3\text{C} \equiv\ \text{CMgX}\).
This reaction highlights the dual nature of terminal alkynes, acting both as weak acids and potential nucleophiles.