A novel synthesis of o-nitrobenzaldehyde by means of the ozonolysis–reductive hydrolysis of symmetrical trans-2,2′-dinitrostilbene is reported, yielding only the ortho isomer of nitrobenzaldehyde. This new route reduces environmental hazards in the synthesis of o-nitrobenzaldehyde. The central ethylene bond of trans-2,2′-dinitrostilbene showed a high reactivity for the ozonolysis reaction. The molecular structures of 2-nitrobenzaldehyde and trans-2,2′-dinitrostilbene were studied theoretically by means of ab initio quantum mechanical calculations at the 6-31G*//6-31G* level. A non-coplanar conformer was found for o-nitrobenzaldehyde, where the carbonyl and nitro groups are slightly twisted with respect to the phenyl ring. Also, a non-coplanar minimal s-trans-gauche/s-trans-gauche conformer (NO₂-aryl-CC-aryl-NO₂) was found for trans-2,2′-dinitrostilbene, where the aromatic groups are twisted with respect to the central double bond, and the nitro groups are also twisted out the planes of the aromatic rings. This structure is consistent with certain experimental physical–chemical properties of this molecule.