Arrange the steps followed during nucleophilic addition on a carbonyl group.

A. \(sp^2\) hybridised carbon of \(>C=O\) group changes to \(sp^3\) hybridised carbon

B. Nucleophile attacks the electrophilic carbon

C. Tetrahedral alkoxide ion is formed

D. Intermediate captures H to give neutral product.

Choose the correct answer from the options given below:

B → A → C → D

The correct answer is option 2. B → A → C → D.

Here is a detailed explanation of the steps involved in the nucleophilic addition to a carbonyl group:

B. Nucleophile Attacks the Electrophilic Carbon

Initial Step: The nucleophilic addition reaction starts when a nucleophile attacks the electrophilic carbon in the carbonyl group.

Reason for Electrophilicity: In the carbonyl group (\(C=O\)), the carbonyl carbon is electrophilic because it is partially positively charged. This positive charge arises from the electron-withdrawing effect of the double-bonded oxygen, which pulls electron density away from the carbon.

Nucleophile: The nucleophile is a species with a pair of electrons that it can donate. Examples include hydroxide ion (\(OH^-\)), cyanide ion (\(CN^-\)), or alcohols in the presence of acidic conditions.

A. \(sp^2\) Hybridized Carbon of \(>C=O\) Group Changes to \(sp^3\) Hybridized Carbon

Change in Hybridization: Upon the nucleophile's attack, the carbonyl carbon, which was originally \(sp^2\) hybridized (due to the double bond with oxygen), undergoes a change to \(sp^3\) hybridization.

Formation of New Bond: This change occurs because the carbon now forms four bonds: one with the nucleophile and one with the oxygen atom, along with two other bonds (typically in a carbonyl compound, the remaining bonds are to other groups or atoms).

C. Tetrahedral Alkoxide Ion is Formed

Formation of Intermediate: The nucleophilic attack on the carbonyl carbon results in the formation of a tetrahedral intermediate. This intermediate is often an alkoxide ion if the nucleophile is an alkyl group.

Structure of Intermediate: The tetrahedral structure is characterized by the central carbon having four substituents, including the nucleophile and the oxygen. The oxygen in the intermediate will have a negative charge due to the extra electron pair from the nucleophile.

D. Intermediate Captures H to Give Neutral Product

Protonation: In the final step, the tetrahedral intermediate often captures a proton, typically from an acidic work-up or solvent, to form a neutral product.

Formation of Final Product: This protonation results in the formation of a product such as an alcohol or another functional group, depending on the nucleophile used. For instance, if the nucleophile is a hydroxide ion (\(OH^-\)), the final product is an alcohol

Summary of the Process

1. Nucleophile attacks the electrophilic carbon: The nucleophile approaches and attacks the carbonyl carbon, leading to the formation of a new bond.

2. Change in hybridization: The carbonyl carbon changes from \(sp^2\) to \(sp^3\) hybridization as it forms four bonds.

3. Formation of tetrahedral intermediate: The result is a tetrahedral intermediate where the carbon is bonded to four groups, and the oxygen typically has a negative charge.

4. Protonation and neutral product formation: The intermediate captures a proton to form the final neutral product.

Therefore, the correct order of the steps in nucleophilic addition to a carbonyl group is: 2. B → A → C → D