Why is aniline less basic than ethylamine

Aniline Is Less Basic Than Ethylamine? -- In-depth Analysis

In the field of chemistry, the strength of alkalinity is closely related to the characteristics of molecular structure. Aniline (C≡H∞NH₂) and ethylamine (C₂ H∞NH₂) are common amine compounds, both of which have an amino (-NH₂) structure, but their basicity is significantly different. Why is the basicity of aniline lower than that of ethylamine? We will analyze the molecular structure, electronic effect and solvent effect in detail.

1. Molecular Structure Difference on Alkalinity

Aniline and ethylamine have similar basic structures and are both composed of an amino group and a hydrocarbon group. The amino group in aniline is directly attached to the benzene ring, while the amino group of ethylamine is attached to an ethyl group (-C? H₂). The benzene ring is a conjugated aromatic system with strong electron attractability.

The electronic influence of the benzene ring on the amino group will reduce the electron density of the amino group, so that the nitrogen atom of the amino group is not easy to provide electrons to the acidic substance, thus reducing its alkalinity. The ethyl group in ethylamine is a slight electron donor, which can provide electrons to the amino group through the I effect (induction effect), enhance the electron density of the amino group, and make it easier to accept protons, so the basicity of ethylamine is higher.

2. electronic effects of different roles

The electronic effect is one of the key factors affecting the alkaline strength. The electronic effect of the benzene ring in aniline on the amino group is an important factor. The π electron system of the benzene ring interacts with the lone pair electron of the amino group through the resonance effect, resulting in the decrease of the electron density of the amino group, making the lone pair electron on the nitrogen atom not easy to participate in the protonation reaction, so the basicity of aniline is low.

In contrast, the ethyl group of ethylamine donates electrons to the amino group by an inductive effect (I effect), thereby increasing the electron density of the amino nitrogen atom, making it more receptive to protons. This electronic effect is more pronounced in ethylamine, making ethylamine more basic than aniline.

3. solvent effect

The solvent environment also has a significant effect on the strength of the alkaline. In aqueous solution, water molecules interact with amino groups and affect the protonation process of amino groups. Because the benzene ring structure of aniline is relatively stable, its solubility in water is low, which leads to the basic inhibition of aniline. The solubility of ethylamine in water is higher, and it can better form hydrogen bonds with water molecules and promote its protonation, so the alkaline performance of ethylamine in water is stronger.

4. conclusion

Through the analysis of the basicity difference between aniline and ethylamine, it can be found that there are two main reasons why the basicity of aniline is lower than that of ethylamine: one is that the benzene ring has a negative effect on the electron density of amino group through resonance effect, and the other is that ethyl group provides electrons to amino group through induction effect to enhance its basicity. Coupled with the effect of the solvent, the alkalinity of ethylamine is more pronounced in aqueous solution.

Why is the basicity of aniline lower than that of ethylamine? It is mainly due to the electron attraction of the benzene ring to the amino group and the electron donor effect of the ethyl group. Understanding these chemical principles is helpful to understand the behavior of amine compounds in different chemical reactions.