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Chemistry Question on Organic Chemistry- Some Basic Principles and Techniques

Which of the following is strongest Bronsted base?

A

Fig 1

B

Fig 2

C

Fig 3

D

Fig 4

Answer

Fig 4

Explanation

Solution

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.