Question

Which of the following is strongest Bronsted base?

• A.

  

• B.

  

• C.

  

• D.

  

Answer 1

The Correct Option is D

To determine the strongest Brønsted base among the given options, we need to understand what a Brønsted base is. A Brønsted base is a substance that can accept protons (H⁺ ions) from other substances. The strength of a Brønsted base is typically determined by its ability to attract and hold onto protons.

Let's examine each option: 

• : Evaluate if this structure can attract protons effectively.
• : Evaluate if this structure can attract protons effectively.
• : Evaluate if this structure can attract protons effectively.
• : Evaluate if this structure can attract protons effectively.

We consider factors such as electron pair availability and electronegativity to determine a molecule's ability to accept protons:

The correct answer is:

This option represents a structure best equipped to accept a proton, making it the strongest Brønsted base among the given choices.

 

Explanation: The ability to accept a proton effectively is often linked to the presence of lone pairs of electrons that are not heavily attracted to a more electronegative atom. In

, the lone pair of electrons is more available for protonation owing to electronic properties that make it a stronger base compared to others which may have lone pairs involved in resonance or closer to electronegative atoms dampening their basicity.

 

Therefore, option

is the strongest Brønsted base.

 

Answer 2

To determine the strongest Bronsted base, we need to evaluate each structure’s ability to accept a proton (H⁺). A stronger Bronsted base has a higher tendency to donate an electron pair to bond with a proton. Let’s examine each structure in detail:

Structure 1: Contains an aromatic amine (aniline derivative) with a nitrogen atom bonded to a benzene ring. The lone pair of electrons on nitrogen is involved in conjugation with the aromatic ring, making it less available for protonation. Therefore, this structure is a weaker Bronsted base due to resonance stabilization of the lone pair.

Structure 2: This is a secondary aromatic amine with two benzene rings attached to nitrogen. Similar to Structure 1, the lone pair on nitrogen is delocalized through resonance with the aromatic rings. The increased resonance further reduces the availability of the lone pair for protonation, making this a weak base.

Structure 3: This structure is a primary amine attached to an alkyl group. While the lone pair on nitrogen is not delocalized through resonance, it is still less basic compared to an aliphatic amine with an sp³-hybridized nitrogen that lacks conjugation.

Structure 4: This structure is a simple cyclic amine with an sp³-hybridized nitrogen atom. The nitrogen has a localized lone pair that is readily available to bond with a proton. Additionally, the sp³-hybridization of nitrogen provides greater electron density due to the lack of resonance or delocalization. Thus, this structure has the strongest tendency to accept a proton, making it the strongest Bronsted base among the options.