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.
  • $\begingroup$ Draw the resonance structures for each of the molecules. $\endgroup$ – AS_1000 Aug 27 '17 at 13:25

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