# Order of reactivity of carbonyl compounds to Nucleophilic addition reaction

One of the questions in my textbook was to arrange the following in order of their reactivity for nucleophilic addition reaction.

1. $\ce{(p-NO2Ph)_2CO}$
2. $\ce{(CH3)_2CO}$
3. $\ce{(p-NO2Ph)COH}$
4. $\ce{CH3COH}$

I know there are two factors in play here. One is the steric factor (4>3>2>1) and annother is the electropositive nature of the carbonyl carbon, which is the site of nucleophilic attack (1>3>4>2). I am unable to decide which of these factors shall overpower the other and what shall be the final order?

Comparing acetone, $\ce{(CH3)2CO}$, to acetaldehyde, $\ce{CH3COH}$, is quite straightforward: acetaldehyde should be the more electrophilic of the two. Firstly, the greater steric bulk of acetone's methyl group slightly hinders nucleophilic attack. Secondly, the additional methyl group is electron-donating by hyperconjugation, comparatively reducing acetone's electrophilicity. Here, both steric effects and electronic effects are synergistic.
Consider p-nitrobenzaldehyde. Sterically, reactivity should be reduced due to the obvious bulk of the aromatic ring. Electronically, the picture seems to me to be more complex. From the perspective of valence bond theory, the $sp^2$ carbons may be electron-withdrawing by induction, particularly in concert with the electronegative nitro group. On the other hand, the carbonyl group is also highly electronegative and should remove electron density from the ring, primarily via the $\pi$ system, and I would expect that effect to be greater. Finally, from the MO theory perspective, considering the frontier orbitals, conjugation of the carbonyl to the aromatic ring should result in lowering the energy of the $\pi^*$ LUMO, which ought to enhance reactivity. That, however, may be mitigated by any overall increase in electron density around the carbonyl group. By comparison to acetaldehyde, the steric effects are clearly unfavorable, while the electronic effects are slightly murky.