Question

The compounds which on reaction with ${\mathrm{CH}}_3\mathrm{Mg}$ I do not give methane are (1) ${\mathrm{CII}}_3{\mathrm{CII}}_2{\mathrm{NII}}_2$ (2) ${\mathrm{C}}_2{\mathrm{II}}_5\mathrm{OII}$ (3) ${\left({\mathrm{CII}}_3\right)}_3\mathrm{N}$ (4) ${\mathrm{NII}}_3$

Short answer

Compound $({\text{CH}}_3{)}_3\text{N}$ does not give methane.

Step-by-step solution

Identify the Reaction Mechanism

When ${\text{CH}}_3\text{MgI}$ is reacted with a compound, it typically acts as a nucleophile and attacks electrophilic centers to form products with methane gas (${\text{CH}}_4$).

Analyze Compound 1

The first compound is ${\text{CH}}_3{\text{CH}}_2{\text{NH}}_2$. Reaction of ${\text{CH}}_3\text{MgI}$ with this results in a nucleophilic attack on the nitrogen atom, leading to the formation of ${\text{CH}}_3{\text{CH}}_2\text{NH}$ along with methane. Thus, this compound gives methane.

Analyze Compound 2

The second compound is ${\text{C}}_2{\text{H}}_5\text{OH}$. Reaction with ${\text{CH}}_3\text{MgI}$ leads to the formation of ${\text{C}}_2{\text{H}}_5{\text{O}}^{-}\text{Mg}\text{I}{\text{CH}}_{3}H$, leading to methane production, so this compound also yields methane.

Analyze Compound 3

The third compound is $({\text{CH}}_3{)}_3\text{N}$. This molecule has no hydrogen atom directly attached to the nitrogen, thus ${\text{CH}}_3\text{MgI}$ will not produce methane upon reaction with it. Therefore, this compound does NOT give methane.

Analyze Compound 4

The fourth compound is ${\text{NH}}_3$. Reaction with ${\text{CH}}_3\text{MgI}$ results in the formation of methane. The reaction would be ${\text{NH}}_3+{\text{CH}}_3\text{MgI}\to {\text{NH}}_2\text{Mg}\text{I}+{\text{CH}}_4$. Thus, this compound also yields methane.

Conclusion

Among the given compounds, only $({\text{CH}}_3{)}_3\text{N}$ does not produce methane when reacted with ${\text{CH}}_3\text{MgI}$.

Key concepts

Nucleophile-Electrophile Interaction

The Grignard reaction showcases an important principle in organic chemistry: the interaction between nucleophiles and electrophiles. This type of reaction is critical for understanding many chemical processes. A nucleophile is a chemical species that donates an electron pair to form a chemical bond. Grignard reagents, such as ${\text{CH}}_3\text{MgI}$, usually act as nucleophiles. An electrophile, on the other hand, is a species that accepts an electron pair. In the reaction described in the exercise, the electrophiles are the different compounds that ${\text{CH}}_3\text{MgI}$ reacts with, like ${\text{CH}}_3{\text{CH}}_2{\text{NH}}_2$ and ${\text{C}}_2{\text{H}}_5\text{OH}$. This interaction leads to the breaking and forming of bonds, resulting in new chemical products. Understanding the roles of nucleophiles and electrophiles helps us predict the outcomes of reactions. It also aids in synthesizing new compounds by selecting appropriate reactants. Always remember, nucleophiles seek positive charges or electron-deficient sites, while electrophiles look for electron-rich zones to interact with.

Methane Production

Methane (\text{CH}_{4}) is a simple hydrocarbon that can be produced during certain chemical reactions, such as the one involving Grignard reagents. Let's break down how this happens. When ${\text{CH}}_3\text{MgI}$ reacts with compounds containing active hydrogen atoms, it results in the formation of methane. For instance, in the case of ${\text{CH}}_3{\text{CH}}_2{\text{NH}}_2$, the following reaction occurs: $${\text{CH}}_3{\text{CH}}_2{\text{NH}}_2+{\text{CH}}_3\text{MgI}\to {\text{CH}}_3{\text{CH}}_2\text{NMgI}+{\text{CH}}_4$$ Similarly, with ethanol (\text{C}_{2}\text{H}_{5}\text{OH}), the reaction proceeds as: $${\text{C}}_2{\text{H}}_5\text{OH}+{\text{CH}}_3\text{MgI}\to {\text{C}}_2{\text{H}}_5\text{OMgI}+{\text{CH}}_4$$ Methane is thus a byproduct of these reactions. However, not all compounds produce methane. For example, $({\text{CH}}_3{)}_3\text{~N}$ does not have a hydrogen ready to be abstracted by ${\text{CH}}_3\text{MgI}$, so methane is not formed.

Reaction Mechanism Analysis

Analyzing the mechanism of the Grignard reaction helps understand why certain compounds yield methane while others do not. The mechanism generally involves the nucleophilic carbon in ${\text{CH}}_3\text{MgI}$ attacking an electrophilic site. Here’s a closer look at the provided compounds.

• ${\text{CH}}_3{\text{CH}}_2{\text{NH}}_2$: The nitrogen atom has a lone pair and an attached hydrogen atom. ${\text{CH}}_3\text{MgI}$ can abstract this hydrogen, yielding methane.
• ${\text{C}}_2{\text{H}}_5\text{OH}$: The oxygen in ethanol is nucleophilic and has an acidic hydrogen. The reaction with ${\text{CH}}_3\text{MgI}$ produces ${\text{CH}}_4$.
• $({\text{CH}}_3{)}_3\text{~N}$: This compound lacks an active hydrogen atom, making it unreactive towards ${\text{CH}}_3\text{MgI}$ in terms of methane production.
• ${\text{NH}}_3$: Ammonia has three hydrogens attached to the nitrogen. Reaction with ${\text{CH}}_3\text{MgI}$ selects one hydrogen, forming methane.

Therefore, the Grignard reaction’s mechanism primarily involves identifying the presence of an active hydrogen atom. This understanding helps in predicting and explaining the outcomes logically.