Why are orthogonally substituted anilines less basic

Why is the orthogonal substitution of aniline alkaline lower?

Aniline is an important organic compound in chemistry, and its basicity is affected by its molecular structure and substituents. The effect of different substituents on the basicity of aniline is a key issue in chemical research, especially the orthogonal substituents. In this paper, we will deeply discuss why the alkalinity of orthogonal substituted aniline is low, and analyze the reason of this phenomenon in detail.

orthogonal substituents on aniline

The basicity of aniline is mainly affected by the electronic interaction between the amino group (-NH₂) and the benzene ring. The amino group acts as an electron donor, donating electrons to the benzene ring through its lone pair of electrons, making the benzene ring part negatively charged, thereby enhancing the basicity of aniline. The position of the substituents can have a significant effect on this electronic effect.

In orthogonally substituted anilines, the substituents are located at the 1,3-position of the phenyl ring, which means that they do not directly produce resonance effects with the amino group. Therefore, orthogonally substituted anilines do not enhance the electron donating ability of the amino group by resonance as ortho-and para-substituted anilines do. This is a key factor in the lower basicity of orthorhombic substituted anilines.

Substituent electronic and spatial effects

The electronic effect of substituents (such as electron withdrawing or electron donating effect) is also a key factor in determining the basicity of aniline. When the aniline molecule is orthogonally substituted, the substituent is usually in the position opposite to the amino group, which makes the direct electronic effect of the substituent on the amino group small. Unlike ortho-or para-substituted anilines, orthogonally substituted anilines cannot significantly affect the electron density of the amino group through direct electron push-pull effects.

Orthogonal substituents often produce spatial effects due to the specificity of their positions, affecting the spatial configuration of the amino group and the interaction with solvent molecules. This steric hindrance effect further reduces the electron density of the amino group, resulting in a lower basicity of the orthorhombic substituted aniline.

ORTHOGONAL SUBSTITUTED ANILINE HYDROGEN BONDING EFFECT

Another potential influence of orthogonal substituents is the formation of hydrogen bonds. In some cases, substituents can interact with the amino group through hydrogen bonding, further affecting the basicity of the aniline. Orthogonal substituents are usually difficult to form effective hydrogen bonds because they are far away from the amino group, which leads to the inability to effectively enhance the electron supply capacity of the amino group, thus affecting the performance of alkalinity.

Summary

The lower basicity of orthogonally substituted aniline is mainly due to the position of the substituent in the molecular structure, which makes it unable to significantly enhance the electron density of the amino group by electronic effect, steric effect or hydrogen bond. Orthogonally substituted aniline due to the lack of effective resonance and direct electronic effects, resulting in its relatively low basicity. This phenomenon has important theoretical significance and practical application value for chemical synthesis and molecular design.