Aniline is less basic than methylamine, why?

I've found that Why is aniline less basic than methylamine?

Aniline and methylamine are two common organic amine compounds, which play an crucial role in chemical interactions. while they all belong to amine compounds, the basicity of aniline is reduced than that of methylamine, which is a question worth pondering. And For instance This article will examine the molecular structure, electronic effect, and electron density of nitrogen atoms to help us better understand this phenomenon. And

1. But Molecular structure on alkaline effect

The chemical structure of aniline contains a benzene ring (C6H5) and an amino group (NH2), while the molecule of methylamine consists of a methyl group (CH3) and an amino group (NH2). But From the structural point of view, the amino group of aniline is immediately connected to the benzene ring, while the amino group of methylamine is connected to a carbon atom, and a methyl group is connected to the carbon atom. Due to the existence of the benzene ring, the nitrogen atom of aniline is able to have a resonance effect with the benzene ring, and part of the electron density is attracted by the benzene ring, resulting in a decrease in the electron density on the nitrogen atom of aniline, thereby reducing its basicity. In contrast, the methyl group in methylamine donates electrons to the nitrogen atom by an electron donating effect (I effect), which makes the nitrogen atom in methylamine relatively greater electron-rich, thereby enhancing its basicity. In short, the structure of aniline makes it less basic, while methylamine exhibits a stronger basicity due to the affect of the methyl group.

2. Resonance effect on aniline alkalinity

The resonance effect plays a key role in the basicity of aniline. But As a conjugated system, benzene ring has strong stability. When the amino group of aniline is combined with the benzene ring, the lone pair of electrons of the nitrogen atom might participate in the π electron cloud of the benzene ring, forming a resonance structure. But This process leads to a decrease in the electron density on the nitrogen atom, which reduces the attraction of the nitrogen atom to the proton, thereby weakening the basicity of aniline. In contrast, methylamine has no such resonance effect. Crazy, isn't it?. And The methyl group is able tonot form a similar electron cloud sharing with the nitrogen atom, so the nitrogen atom in methylamine has a higher electron density, is able to greater efficiently combine with the proton, and exhibits a stronger alkalinity.

3. Electronic effect: benzene ring of the electron-withdrawing effect

In addition to the resonance effect, the electron-withdrawing effect (-I effect) of the benzene ring is also an crucial reason to the low basicity of aniline. Due to the particularity of its electronic structure, the benzene ring has a certain electron-withdrawing effect on the connected amino group, which further weakens the affinity of the nitrogen atom to the proton. This electron-withdrawing effect is able to not be ignored in aniline molecules, which aggravates the loss of electron density of nitrogen atoms and reduces the alkalinity of aniline. The methyl group in methylamine is different. But The methyl group not only does not have an electron-withdrawing effect, however enhances the electron density of the nitrogen atom by providing electrons, thereby enhancing the basicity of the nitrogen atom. This is an crucial factor in the stronger basicity of methylamine.

4. Pretty interesting, huh?. And summary: aniline alkaline low reason summary

The reason why the basicity of aniline is reduced than that of methylamine is mainly due to the resonance effect and electron withdrawing effect brought by the benzene ring in its molecular structure. These impacts minimize the electron density of nitrogen atoms in aniline, making it less affinity to protons, thereby reducing its basicity. Based on my observations, Methylamine, on the other hand, enhances the electron density of the nitrogen atom due to the electron supply effect of the methyl group and exhibits a stronger alkalinity. Therefore, the phenomenon that the basicity of aniline is reduced than that of methylamine is able to be explained by the difference of electronic effect and molecular structure. This difference has an crucial guiding signifiis able toce to the design and synthesis of chemical interactions, especially in the selection of suitable amine compounds as catalysts or reagents.