Question

The product \(\mathrm{P}\) in the following reaction is \(\mathrm{ClCH}_{2}-\mathrm{CH}_{2} \mathrm{OH} \stackrel{\mathrm{OH}^{-}}{\longrightarrow} \mathrm{P}\)

Short answer

Answer: The product P formed in this reaction is 2-hydroxyethanal (H2C=OCH2OH).

Step-by-step solution

Identify the reactive part of the molecule

In this reaction, the hydroxide ion (OH-) acts as a nucleophile, which means it has a high electron density and will look for a somewhat positively charged part of the molecule to react with. In this case, the carbon atom attached to the chlorine atom in ClCH2-CH2OH can acquire a partial positive charge since chlorine is more electronegative than carbon. This makes the carbon atom electrophilic and susceptible to nucleophilic attack by the hydroxide ion.

Nucleophilic attack and formation of a possible intermediate

The hydroxide ion (OH-) attacks the somewhat positively charged carbon atom in the molecule, forming a possible intermediate. In this intermediate, the carbon has a single bond with the chlorine atom, a single bond with the CH2OH group, and a single bond with the hydroxide ion.

Elimination of chloride ion

In the next step, the chlorine atom leaves the molecule as a chloride ion (Cl-). This is an elimination step, and the C-O bond is now a double bond (C=O). The intermediate transforms into the final product.

Identify the product P

After the elimination of the chloride ion, the final product P is formed. The structure of the product is H2C=OCH2OH, which is an aldehyde group (-CHO) attached to the CH2OH group. In IUPAC nomenclature, the compound is named as 2-hydroxyethanal.

Key concepts

Electrophilic Carbon

In the realm of chemical reactions, particularly nucleophilic substitutions, understanding the concept of electrophilic carbon is crucial. Electrophilic carbon refers to a carbon atom within a molecule that is prone to attracting electrons due to its partial positive charge.
This partial positive charge often arises because the carbon is bonded to a more electronegative atom, such as chlorine. In the example of the given reaction, the carbon atom bonded to chlorine in \[\text{ClCH}_2\text{-CH}_2\text{OH}\] displays electrophilic characteristics. Here’s why:

• Chlorine, being more electronegative, pulls electrons towards itself, leaving the carbon slightly positive.
• This positive character makes the carbon susceptible to nucleophilic attack.
• As a result, such carbon is termed as electrophilic, making it an ideal target for nucleophiles in reactions.

Understanding electrophilic carbon provides insights into reaction mechanisms, particularly those involving nucleophiles attacking and forming new bonds.

Hydroxide Ion as Nucleophile

Nucleophiles are species that donate electron pairs to electrophilic centers, and hydroxide ions (\(\text{OH}^-\)) are a common example. They are negatively charged and thus rich in electrons.
This high electron density makes hydroxide ions eager to donate electrons to positively charged or partially positive atoms.In the reaction provided, the hydroxide ion serves as the nucleophile. It plays a pivotal role in carrying out the nucleophilic substitution. Key aspects include:

• The hydroxide ion attacks the electrophilic carbon, which is bonded to the chlorine atom.
• Due to its negative charge, the hydroxide ion easily approaches and forms a bond with the carbon.
• This interaction is crucial because it sets the stage for further transformations, such as creating intermediates or leading to final products through the release of other ions, like chloride.

Emphasizing the action of the hydroxide ion highlights the elegance of chemical reactions, where electron-rich species find and bond with electron-poor partners.

Elimination Reaction

Elimination reactions are common in organic chemistry, where parts of a molecule are removed, resulting in the formation of unsaturated compounds, like alkenes or carbonyls.
In our given reaction, the elimination step plays a vital role in the transformation of the substrate.Once the hydroxide ion performs a nucleophilic attack on the electrophilic carbon, the next crucial step is the elimination of the chloride ion, as follows:

• After the hydroxide forms a bond with the electrophilic carbon, chlorine departs as a chloride ion (\( \text{Cl}^- \)), a classic elimination process.
• This removal results in a transformation that changes the single bond between carbon and oxygen in the hydroxyl group to a double bond, forming a carbonyl group.
• As a result, the intermediate sheds atoms, moving from a saturated to an unsaturated state, specifically forming the carbonyl moiety of the aldehyde, 2-hydroxyethanal.

This step marks the completion of the reaction mechanism, showcasing how molecules can undergo profound transformations through targeted elimination.