How does MO theory explain the effect of directing groups on aromatic compounds?

From what I could find, this is usually explained using resonance. For example,
[![Explanation of the meta-directing effect of a nitro group on a benzene ring](https://i.stack.imgur.com/mJGK1.png)](https://i.stack.imgur.com/mJGK1.png)


*from Wade's Organic chemistry, 9th edition, p. 823.*


but I can't figure out how to see this through the MOs of the molecule. If the lowest energy MO is two toruses above and below the aromatic ring, then in this case, the addition of the electrophile E sort of "breaks" that torus, but isn't the remaining orbital just two "C shaped" densities, in each case equally capable of delocalizing the positive charge?




**Disclaimer:** all calculations were performed using [MolCalc](https://molcalc.org/), an excellent web-based tool to quickly calculate quantum mechanical properties of a molecule.


### Debunking the Misconceptions


1. Lowest energy MO is not two toruses above and below the aromatic ring, it is the two $\mathrm{1s}$ *orbitals* of $\ce{O}$ in the nitro group of **nitrobenzene** at -551.12 eV (essentially not interacting).
2. The torus didn't disappear upon substitution of the nitro group. The *toruses* are still present at -13.27 eV.


[![potential surface diagram of symmetric pi electron density of nitrobenzene](https://i.stack.imgur.com/J74Fv.png)](https://i.stack.imgur.com/J74Fv.png)


3. The torus didn't break. Even upon substitution of the -chloro group at the para position, the *toruses* can still be found at -14.35 eV.


[![potential surface diagram of symmetric pi electron density of p-chloronitrobenzene](https://i.stack.imgur.com/tLX0O.png)](https://i.stack.imgur.com/tLX0O.png)


### Explanation using Molecular Orbitals Theory


According to [ChemLibreTexts](https://chem.libretexts.org/Courses/Brevard_College/CHE_201%3A_Organic_Chemistry_I/04%3A_Aromatic_Compounds_(Arenes)/4.11%3A_Electrophilic_Aromatic_Substitution_Reactions_of_Benzene_Derivatives), -$\ce{NO2}$ is a *deactivation* group, reducing the electron density at ortho and para positions, as explained by the resonance structures as well, but this is not so easily seen in the molecular orbital diagrams.


These are the second and third occupied molecular orbitals of nitrobenzene (the first is localized on the nitro group):


[![Second and third highest occupied molecular orbitals of nitrobenzene](https://i.stack.imgur.com/msBCQ.png)](https://i.stack.imgur.com/msBCQ.png)


The second highest occupied molecular orbital shows no electron density at the para position and the third highest occupied molecular orbital shows low electron density at the ortho position.


### Caution


Electrons are not actually filled exactly according to the Aufbau principle, since there is always some thermal energy. Furthermore, the interaction is far more complex than singly pointed out molecular orbitals. Moreover, the calculations by MolCalc (being a fast tool) are not very accurate and you need to use more sophisticated software tools and analyze transition states to get a clear picture.


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