Question

The reaction: \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{I}+\mathrm{KOH}(\mathrm{aq}) \rightarrow \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}+\mathrm{KI}\) is classified as : (a) electrophilic substitution (b) nucleophilic substitution (c) elimination (d) addition

Short answer

The reaction is a nucleophilic substitution.

Step-by-step solution

Identify the Reactants

The reaction involves ethyl iodide (\( \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{I} \)) and aqueous potassium hydroxide (\( \mathrm{KOH(\mathrm{aq})} \)).

Key concepts

Ethyl Iodide

Ethyl iodide is an organic compound composed of ethyl group \(\left( \text{–CH}_3\text{CH}_2\right)\) and an iodine atom chemically bonded to it. With its molecular formula being \(\mathrm{C}_{2}\mathrm{H}_{5}\mathrm{I}\), it is often referred to as iodoethane. In chemical reactions, ethyl iodide acts as a good substrate for nucleophilic substitutions due to the properties of its carbon-iodine bond.Here's why ethyl iodide is particularly reactive: - **Weak C-I bond**: The bond between carbon and iodine is relatively weak due to iodine's large atomic size. Once iodine leaves, it provides a chance for nucleophilic attacks. - **Iodine's electronegativity**: This atom is also more electronegative than carbon and tends to hold the electrons tightly, facilitating easy breakage of the C-I bond.In a reaction setting, ethyl iodide often acts as an electrophile, creating a site for nucleophiles to attack and replace the iodine atom. This makes it an excellent candidate for demonstrating the nucleophilic substitution reaction, as in the given example with potassium hydroxide.

Potassium Hydroxide

Potassium hydroxide (KOH) is typically found as a colorless solid and is known for its strong alkaline properties. Being a strong base, when dissolved in water, it dissociates fully to provide hydroxide ions (OH⁻), which play a critical role in nucleophilic reactions.Here’s how KOH works in the reaction:- **Source of Nucleophiles**: The hydroxide ion \(\text{OH}^-\) is an excellent nucleophile. It readily attacks positively polarized centers in molecules, such as the carbon atom in ethyl iodide.- **Reactant in Aqueous Solution**: When KOH is in an aqueous solution, it aids in the smooth occurrence of substitution reactions by maintaining a medium that facilitates ion movement.In the outlined reaction, KOH's hydroxide ion targets and replaces the iodine atom in ethyl iodide, resulting in the formation of ethyl alcohol \(\left(\text{C}_2\text{H}_5\text{OH}\right)\). This transformation underscores the role of KOH as a powerful agent in enabling nucleophilic substitution.

Reaction Classification

Understanding the classification of reactions is essential in chemistry, as it helps predict the products and mechanisms involved. In the context of the given exercise, the transformation of ethyl iodide and potassium hydroxide into ethanol and potassium iodide is classified as a nucleophilic substitution reaction.Let’s see why it holds this classification:- **Nucleophile Involvement**: A nucleophilic substitution reaction generally involves a nucleophile. In this case, the hydroxide ion \(\text{OH}^-\) acts as the nucleophile.- **Substitution Process**: The nucleophile attacks an electrophile to replace a leaving group. Here, the hydroxide ion attacks the carbon atom in ethyl iodide, displacing the iodine and forming a new bond to create ethanol.This reaction serves as a classic example of a \( \text{S}_\text{N}2 \) mechanism, which is a concerted process where the nucleophilic attack and the leaving of the iodide ion happen simultaneously. This makes nucleophilic substitution a fundamental reaction type, particularly when studying organic chemistry.