Question

Ch3MgBr+ROH with mechanism

Answer 1

The reaction yields methane gas and a magnesium alkoxide.

$CH_3MgBr + ROH \longrightarrow CH_4 + ROMgBr$

Answer 2

Explanation of the Solution:

The reaction between Methylmagnesium bromide ($CH_3MgBr$), a Grignard reagent, and an alcohol ($ROH$) is a classic acid-base reaction.

1. Grignard Reagent as a Base: In $CH_3MgBr$, the carbon atom of the methyl group is bonded to magnesium. Due to the significant electronegativity difference between carbon and magnesium, the C-Mg bond is highly polarized, giving the carbon atom a substantial negative charge (acting like a carbanion, $CH_3^-$). This makes the methyl group a very strong base.

2. Alcohol as an Acid: Alcohols ($ROH$) contain a hydroxyl group (-OH). The hydrogen atom bonded to the electronegative oxygen is acidic, meaning it can be easily abstracted as a proton ($H^+$).

3. Proton Transfer: The highly basic methyl group ($CH_3^-$) from the Grignard reagent abstracts the acidic proton from the alcohol. This is a rapid proton transfer reaction.

Mechanism:

\begin{center} $CH_3MgBr + ROH \longrightarrow CH_4 \uparrow + ROMgBr$ \end{center}

1. Step 1: Proton Abstraction

   The electron-rich methyl carbon of $CH_3MgBr$ acts as a strong base and attacks the electrophilic (acidic) hydrogen of the alcohol.

   \begin{center} $CH_3^{\delta-} \text{---} MgBr^{\delta+} \quad + \quad R \text{---} O^{\delta-} \text{---} H^{\delta+}$ \end{center}

   • A curved arrow originates from the electron pair (or the negative charge) on the methyl carbon of $CH_3MgBr$ and points towards the acidic hydrogen of $ROH$. This signifies the formation of the new C-H bond.

   • Simultaneously, another curved arrow originates from the O-H bond in $ROH$ and points towards the oxygen atom. This signifies the breaking of the O-H bond and the electrons moving onto the oxygen, forming an alkoxide ion ($RO^-$).

2. Step 2: Product Formation

   This results in the formation of:

   • Methane ($CH_4$): A gaseous hydrocarbon, formed by the protonation of the methyl group.

   • Magnesium Alkoxide ($ROMgBr$): A salt-like compound formed by the association of the alkoxide ion ($RO^-$) with the $MgBr^+$ counterion.

Visual Representation (Arrow Pushing):