Aniline is a weaker base

In the field of chemistry, the strength of a basic substance is usually determined by its proton accepting ability (that is, hydrogen ion accepting ability). Aniline and ethylamine are two common amine compounds, which have some differences in acidity and basicity. Why is the problem that aniline is a weaker base than ethylamine? This article will analyze this problem in detail to help readers better understand the difference in basicity between these two compounds.

1. Aniline and ethylamine structure difference

The difference in molecular structure between aniline and ethylamine is an important reason for the different alkalinity. Aniline (C6H5NH2) contains a benzene ring, while ethylamine (C2H5NH2) contains an ethyl (C2H5) substituted amino (-NH2) group.

The benzene ring is a highly stable aromatic compound whose π electron cloud can resonantly interfere with the lone pair electrons of the nitrogen atom. Since the electron cloud of the benzene ring resonates with the lone pair electron of the nitrogen atom, the lone pair electron of the nitrogen atom in aniline becomes less likely to participate in the acceptance of the proton, thereby reducing the basicity of aniline.

Relatively speaking, the structure of ethylamine is relatively simple, and the existence of ethyl does not have a significant effect on the lone pair electron of the nitrogen atom, so the lone pair electron of the nitrogen atom of ethylamine can be more easily combined with the proton, showing a strong basicity.

2. Electronic effect on alkaline effect

The electronic effect is another key factor in the analysis of the basicity difference between aniline and ethylamine. The benzene ring in aniline has a certain attraction to the electron density of the nitrogen atom. The π electron cloud in the benzene ring attracts a part of the electrons from the nitrogen atom through the resonance effect, which reduces the density of the lone pair electrons on the nitrogen atom, resulting in a decrease in its ability to attract protons, thereby reducing the alkalinity of aniline.

In ethylamine, the ethyl group is an electron donor group. It donates electrons to the nitrogen atom through the I effect, so that the density of lone pair electrons on the nitrogen atom increases, thereby enhancing the affinity of the nitrogen atom for the proton, which makes the ethylamine more basic.

3. Nitrogen atom lone pair electron availability

In acid-base reactions, the lone pair of electrons on the nitrogen atom is an important factor in determining its basicity. Due to the interference of the benzene ring, the availability of the lone pair electron of the nitrogen atom of aniline is limited and cannot be effectively combined with the proton. In contrast, the nitrogen atom lone pair electron of ethylamine is not disturbed by a similar electronic effect, so its lone pair electron is more active and can accept hydrogen ions more easily, thus showing a stronger basicity.

4. Conclusion: Aniline is indeed a weaker base

It can be concluded from the above analysis that aniline is a weaker base than ethylamine. The fundamental reason for this phenomenon is that the benzene ring in aniline interferes with the resonance of the lone pair electrons of the nitrogen atom, while the ethyl group in ethylamine enhances the lone pair electron density of the nitrogen atom through the electron donor effect, making it more basic. Understanding this is of great significance for the prediction and optimization of chemical reactions, especially in the preparation and use of amine compounds, the selection of appropriate amine substances has a direct impact on the efficiency and selectivity of the reaction.

I hope this article can help you better understand the difference between aniline and ethylamine in alkalinity.