Fundamentals of Organic ChemistryChemistryHaloalkanes and Haloarenes
When cyclohexyl chloride reacts with ammonia ( NH ₃ ) to form cyclohexylamine, the reaction does not go to completion if only one equivalent of NH ₃ is used. Which of the following best explains this observation?
Options
- AChloride is a poor leaving group, so more NH ₃ is needed to increase the reaction rate.
- BThe cyclohexyl group presents significant steric hindrance, requiring an excess of NH ₃ to proceed.
- CThe HCl generated during the reaction protonates NH ₃ , forming NH ₄⁺ which is not nucleophilic.
- DNH ₃ is a weak nucleophile, so a large excess is needed to drive the equilibrium forward.
Correct answer
C. The HCl generated during the reaction protonates NH ₃ , forming NH ₄⁺ which is not nucleophilic.
Step-by-step solution
The reaction of cyclohexyl chloride with ammonia proceeds via nucleophilic substitution: C ₆ H ₁₁ Cl + NH ₃ C ₆ H ₁₁ NH ₂ + HCl The HCl produced is a strong acid and immediately reacts with the unreacted basic ammonia ( NH ₃ ) to form ammonium chloride: NH ₃ + HCl NH ₄⁺ + Cl ⁻ The ammonium ion ( NH ₄⁺ ) lacks a lone pair of electrons and is therefore not nucleophilic. Because one molecule of NH ₃ is consumed by the HCl produced for every molecule of cyclohexyl chloride that reacts, using only one equivalent of NH ₃