# Order of acidity in aromatic molecules with various functional groups

What factors need to be considered in order to rank the acidity of aromatic molecules with various substituents?

Given benzene with 1 $\ce{OH}$ group. How does adding the following functional groups affect acidity, and what are the rules to determine this?

• an additional $\ce{OH}$ group
• $\ce{Cl}$
• $\ce{NO2}$
• $\ce{NO2 + Cl}$
• $2\times\ce{NO2}$ groups
• $3\times\ce{NO2}$ groups

Based on what I know about acids, the following increase acidity:

• charge - the less electrons, the more acidic (more able to grab hydrogen)
• electronegativy increases.
• compounds with more resonance (more double and triple bonds) - more stability.
• more electron withdrawing groups.
• lower orbitals - the more s character (less p,d,f), the closer the electrons are to the nucleus, and the lower the energy, which means more stability.

The following decreases acidity

• steric hindrance - where 3D structure of a molecule make solvent less accessible, and thus more weakly stabilised. (The difference may be small)
• larger molecules tend to require a larger number of solvent molecules to solvate them.
• Draw the resonance structures for each of the molecules. – AS_1000 Aug 27 '17 at 13:25