Final answer:
When ortho and para positions are occupied on an aromatic compound, a CHO group would attach at the meta position.
Step-by-step explanation:
If the ortho and para positions on an aromatic compound are already occupied, and the compound undergoes a reaction where a CHO group (i.e., an aldehyde functional group) needs to be attached, the CHO group would attach at the meta position relative to the existing substituents.
This is because in the common nomenclature of disubstituted benzene rings, the prefixes ortho-, meta-, and para- describe the relative positions of groups attached to the aromatic ring, with ortho indicating adjacent positions, meta indicating a 1,3 arrangement, and para indicating a 1,4 arrangement. When ortho and para positions are blocked, by default, the CHO group would have to attach at the remaining unfilled position, which would be the meta position.