1. Identify the reactants

   • Carbonyl compound: cyclohexanone (a ketone)
   • Amine: dimethylamine, which is a secondary amine
   • Conditions: catalytic acid and continuous removal of water

2. Recall the general reaction of carbonyl compounds with amines

   Carbonyl compounds react with amines by nucleophilic addition followed by dehydration.

   • With a primary amine, the product is an imine (also called Schiff base in many cases): $R_2C=O + R'NH_2 \rightarrow R_2C=NR' + H_2O$

   • With a secondary amine, the product is generally an enamine: $\text{ketone} + \text{secondary amine} \xrightarrow[\text{remove }H_2O]{H^+} \text{enamine}$

3. Why not imine/Schiff base here?

   Dimethylamine is $(CH_3)_2NH$, a secondary amine. Formation of an imine requires a nitrogen atom that still has one hydrogen initially and can end up double-bonded to carbon after loss of water. Secondary amines instead give an intermediate iminium ion, followed by loss of an $\alpha$-hydrogen to form an enamine.

4. Role of removing water

   Since the reaction is reversible, continuous removal of water drives the equilibrium toward the condensation product by Le Chatelier’s principle.

5. Conclusion

   Therefore, cyclohexanone reacts with dimethylamine under acidic conditions to form an enamine.

6. Option check

   • A: Schiff’s base $\rightarrow$ formed typically with primary amines, not secondary amines
   • B: enamine $\rightarrow$ correct
   • C: imine $\rightarrow$ not with a secondary amine
   • D: amine $\rightarrow$ incorrect

Hence, the correct answer is B.