Which Aniline Derivative Is More Basic: Ortho or Para Substituted?

[atavistic]

Homework Statement

Which isomer is more basic in the following pairs:

o-methyl aniline or p-methyl aniline

o-chloro aniline or p - chloro aniline

o - chloro aniline or o-floro aniline

o-nitro aniline or p-nitro aniline

 

[Spirochete]

I'd think about this in terms of factors that either stabilize or destabilize the positive charge on nitrogen after it accepts a proton. For example if the charge is destabilized more it means the conjugate base must be weaker.

 

[Blueshift5]

I would like to clarify that the term "isomer" refers to molecules that have the same chemical formula but different arrangements of atoms. Therefore, the provided pairs do not represent isomers, but rather positional isomers or regioisomers.

In regards to acidity/basicity, the basicity of a compound is determined by the availability of an electron pair to accept a proton. Generally, a compound with a higher electron density or a more basic functional group will have a higher basicity.

Based on this, it can be predicted that the o-methyl aniline and o-fluoro aniline will be more basic than their respective p-isomers. This is because the methyl and fluoro groups are electron-donating, increasing the electron density on the nitrogen atom and making it more basic.

However, in the case of o-chloro aniline and p-chloro aniline, both compounds have the same functional group, but the position of the chlorine atom changes. In this case, it is difficult to predict which isomer will be more basic without experimental data. This is because the position of the chlorine atom can affect the electron density on the nitrogen atom in different ways, making it difficult to determine which isomer will have a higher basicity.

Similarly, the basicity of o-nitro aniline and p-nitro aniline cannot be predicted without experimental data. The nitro group is a strong electron-withdrawing group, which can decrease the electron density on the nitrogen atom and make it less basic. However, the position of the nitro group can also affect the electronic effects on the nitrogen atom, making it difficult to determine which isomer will be more basic.

In conclusion, the basicity of positional isomers cannot be predicted with certainty and would require experimental data for accurate comparison.