One of the products formed in the following reaction is
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Grignard reagents are aggressive proton-seekers! If a compound contains an active hydrogen like in $\text{H}_2\text{O}$, R-OH, $\text{R-NH}_2$, or R-COOH, the Grignard reagent will immediately abstract it to form an alkane (R-H), bypassing any potential carbon-carbon coupling pathways.
Concept:
Grignard reagents (R-MgX) are highly reactive organometallic compounds. Because the carbon-magnesium bond is strongly polarized with a high degree of ionic character, the alkyl group behaves as an exceptionally powerful base ($\text{R}^-$) as well as a strong nucleophile.
When a Grignard reagent encounters any chemical species containing an active (acidic) hydrogen atom attached directly to a highly electronegative element like oxygen (-OH), nitrogen ($\text{-NH}_2$), or sulfur (-SH), an acid-base proton-transfer reaction takes place immediately. This protonation deactivates the Grignard carbon, converting it into its corresponding stable alkane (R-H). This rapid decomposition pathway is widely known as the Zerewitinoff reaction.
Step 1: Identifying the reactive centers in the reactants.
Let us inspect the two organic molecules participating in the given reaction:
1) Reactant 1: Cyclohexylmagnesium bromide ($\text{C}_6\text{H}_{11}\text{MgBr}$). Here, the cyclohexyl ring carbon bound to magnesium acts as a powerful carbanionic base:
\[
\text{R}^- = \text{C}_6\text{H}_{11}^- \quad (\text{Cyclohexyl carbanion})
\]
2) Reactant 2: Cyclohexylamine ($\text{C}_6\text{H}_{11}\text{NH}_2$). Primary amines possess active hydrogen atoms directly bonded to a nitrogen atom. These N-H protons are weakly acidic and can be readily abstracted by strong bases:
\[
\text{R'-NH}_2 \rightleftharpoons \text{R'-NH}^- + \text{H}^+
\]
Step 2: Formulating the step-by-step reaction mechanism.
The reaction behaves as an instantaneous acid-base neutralization rather than a nucleophilic substitution or coupling reaction. The strongly basic carbanion site on the cyclohexyl ring attacks and abstract one of the acidic protons from the amino group of cyclohexylamine:
\[
\text{C}_6\text{H}_{11}\text{-MgBr} + \text{H-NH(C}_6\text{H}_{11}) \longrightarrow \text{C}_6\text{H}_{11}\text{-H} + [\text{C}_6\text{H}_{11}\text{-NH}]^-\text{MgBr}^+
\]
Step 3: Identifying the structure of the final products.
Let us characterize the products formed from this transformation:
• The cyclohexyl carbanion gains a proton ($\text{H}^+$) to form cyclohexane ($\text{C}_6\text{H}_{12}$).
• The remaining amide anion coordinates with the magnesium salt to form a magnesium halide complex byproduct: $\text{C}_6\text{H}_{11}\text{NHMgBr}$.
The question asks for "one of the products formed". Looking at the options, Option (1) represents a pure, unsubstituted cyclohexane ring ($\text{C}_6\text{H}_{12}$), which perfectly matches our main product.
