Introduction:
Aniline is an aromatic amine with the molecular formula C6H5NH2. It is a weakly basic compound that can exist in both neutral and protonated forms. In aqueous solution, aniline shows UV absorption maxima at different wavelengths than benzene. However, in a solution of pH=1, the position of UV absorption maxima of aniline becomes almost identical to those of benzene. This phenomenon can be explained by the effect of pH on the chemical structure of aniline.

Effect of pH on aniline:
When aniline is dissolved in water, it can exist in three different forms: neutral, cationic, and anionic. At neutral pH, aniline exists mostly in the neutral form, which has a lone pair of electrons on the nitrogen atom. This lone pair can interact with the pi-electron cloud of the benzene ring, causing a shift in the position of the UV absorption maxima. The interaction between the lone pair and the pi-electron cloud leads to a decrease in the energy required to excite an electron from the ground state to the excited state, resulting in a shift in the position of the absorption maxima to a higher wavelength.

Effect of pH on benzene:
Benzene is a nonpolar compound that does not interact with water molecules. Therefore, its position of UV absorption maxima does not change with changes in pH. However, in a solution of pH=1, benzene can undergo protonation to form the benzene cation. The benzene cation has a positive charge delocalized over the six carbon atoms, which leads to a shift in the position of the absorption maxima to a lower wavelength.

Effect of pH on aniline in acidic solution:
In a solution of pH=1, aniline exists mostly in the cationic form, which is protonated on the nitrogen atom. The protonation of the nitrogen atom removes the lone pair of electrons, and the interaction with the pi-electron cloud of the benzene ring is lost. Therefore, the position of the UV absorption maxima of aniline in a solution of pH=1 becomes almost identical to those of benzene.

Conclusion:
The position of UV absorption maxima of aniline in aqueous solution is different from those of benzene due to the interaction between the lone pair of electrons on the nitrogen atom and the pi-electron cloud of the benzene ring. However, in a solution of pH=1, aniline exists mostly in the cationic form, and the interaction is lost. Therefore, the position of the UV absorption maxima of aniline becomes almost identical to those of benzene.