Question

Which compound(s) on reaction with \(\mathrm{NaHCO}_{3}\) gives lactone as a product? (A) \(\alpha\)-Bromo carboxylic acid (B) \(\beta\)-Bromo carboxylic acid (C) \(\gamma\)-Bromo carboxylic acid (D) \(\delta\)-Bromo carboxylic acid

Short answer

The compound(s) that can react with sodium bicarbonate to give lactone as a product are (B) β-Bromo carboxylic acid and (C) γ-Bromo carboxylic acid.

Step-by-step solution

Write out the structures of the given compounds

First, let's start by writing the structures of α-Bromo carboxylic acid, β-Bromo carboxylic acid, γ-Bromo carboxylic acid, and δ-Bromo carboxylic acid: (A) α-Bromo carboxylic acid: \(\mathrm{BrCH_{2}COOH}\) (B) β-Bromo carboxylic acid: \(\mathrm{CH_{2}BrCH_{2}COOH}\) (C) γ-Bromo carboxylic acid: \(\mathrm{CH_{2}CH_{2}BrCH_{2}COOH}\) (D) δ-Bromo carboxylic acid: \(\mathrm{CH_{2}CH_{2}CH_{2}BrCH_{2}COOH}\)

Determine which bromo carboxylic acid reacts to form lactone

Now that we have the structures, we need to identify which bromo carboxylic acid can react intramolecularly to form a lactone when treated with sodium bicarbonate. (A) In the case of α-Bromo carboxylic acid, the bromine atom is too close to the carboxyl group, making it unlikely to participate in an intramolecular reaction, as it would lead to an unstable two-membered ring. (B) For β-Bromo carboxylic acid, an internal reaction would lead to the formation of a stable five-membered ring, which is possible. (C) In the case of γ-Bromo carboxylic acid, an internal reaction would result in a six-membered ring, which is also possible. (D) For δ-Bromo carboxylic acid, the bromine atom is too far away from the carboxyl group, making it unlikely to participate in an intramolecular reaction, as it would involve the formation of a seven-membered ring which is less favored. So, the compound(s) that can react with sodium bicarbonate to give lactone as a product are (B) β-Bromo carboxylic acid and (C) γ-Bromo carboxylic acid.

Key concepts

Intramolecular Reaction

An intramolecular reaction is a chemical reaction in which bonds are formed between atoms in the same molecule. This is contrasted with intermolecular reactions, where bonds are formed between atoms in different molecules. In the context of lactone formation, an intramolecular reaction involves a nucleophilic atom or group within the molecule attacking an electrophilic carbon within the same molecule. This typically leads to the creation of a cyclic structure.

Here are some key points about intramolecular reactions that you can remember:

• The reaction occurs within the same molecule.
• It often results in the formation of a ring structure, known as a lactone when involving carboxylic acids.
• The proximity of the reactive groups significantly influences the likelihood and efficiency of the reaction.

This concept is essential to understand because it helps explain why certain bromo carboxylic acids preferentially form lactones over others.
In the presence of a base like sodium bicarbonate (\(\mathrm{NaHCO}_{3}\)), the hydrogen is removed from the carboxylic acid, facilitating the nucleophilic attack that leads to rings.

Bromo Carboxylic Acids

Bromo carboxylic acids are specific types of carboxylic acids where a bromine atom is attached to the carbon atom adjacent to the carboxyl group. This bromine group serves as a potential leaving group during a reaction. When bromo carboxylic acids undergo intramolecular reactions, the bromine atom leaves, helping to form a lactone.

• Alpha (\(\alpha\)) bromo carboxylic acid has the bromine attached directly to the carbon that is also connected to the carboxyl group. Its proximity may prevent intramolecular reactions due to ring strain.
• Beta (\(\beta\)) bromo carboxylic acid has the bromine one carbon away from the carboxyl group; typically forms a five-membered ring.
• Gamma (\(\gamma\)) bromo carboxylic acid places the bromine two carbons away, allowing formation of a six-membered ring.
• Delta (\(\delta\)) bromo carboxylic acid positions the bromine even further, leading to less favorable seven-membered rings.

Understanding these structures is crucial for predicting which acids can successfully form lactones through intramolecular reactions.
This knowledge especially helps determine product stability and reaction feasibility in organic synthesis.

Ring Stability

The stability of a ring is a critical consideration when determining if and how a lactone will form during an intramolecular reaction. Rings vary in stability based on their size and conformational strain. Typically, five- and six-membered rings are more stable than smaller or larger rings.

• Two- or three-membered rings usually have significant angle strain and are less favorable.
• Five-membered rings, like those formed from \(\beta\)-bromo carboxylic acids, are more stable due to minimized angle strain.
• Six-membered rings, which can be formed from \(\gamma\)-bromo carboxylic acids, are even more stable and often represent the ideal conformation.
• Seven-membered rings and beyond can result in torsional strain due to their size, making them less stable.

The preference for forming a five- or six-membered ring during lactone formation directly influences the chemical behavior and reactivity of the bromo carboxylic acids involved.
Thus, the selection of which bromo carboxylic acid to use in a reaction with sodium bicarbonate ultimately hinges on an understanding of ring stability.