Question

Which compound, M or N, is the stronger acid? Explain your choice.

Short answer

M is the stronger acid.

Step-by-step solution

Determination of strong organic acids

In organic chemistry, strong acids are determined based on the tendency to release protons.

The electron-withdrawing group increases the acidic strength of the compound. The electron-donating group decreases the acidic strength of the compound.

Mechanism for M compound

In compound M, the OH group-containing positive charge is adjacent to the methyl group. The methyl group donates its electron towards carbonyl oxygen through the inductive effect.

Therefore, the electrons cannot be transferred rapidly to decrease the electrophilicity of oxygen. Hence, the compound releases proton quickly. Hence, the compound is more acidic.

Donation of electrons through +I effect

Mechanism for N compound

In compound N, the OH group-containing positive charge is adjacent to the ethoxy group. The ethoxy group donates its electron towards carbonyl oxygen through a mesomeric effect (donation of non-bonding electrons).

Therefore, the electrons are transferred rapidly to decrease the electrophilicity of oxygen. Hence, the compound does not release protons quickly.

Therefore, the compound is the least acidic.

Donation of electrons through +M effect