Substituent Effect on N-Benzylideneanilines by DFT Energy Partition

To investigate the substituent effect on x-electron delocalization of the N-benzylideneaniline （NBA）, the vertical resonance energies △E^V（θ） of eleven substituted NBAs were separated into n and a parts at the B3LYP/6-311G（d） level of the Density Functional Theory （DFT）. When substituted with an electron-releasing group --OH, the calculated △E^V（θ） of NBA was increased, indicative of more resonance destabilization than the mother molecule. However, when substituted with an electron-withdrawing group -NO2, the calculated △E^V（θ） values indicated less resonance destabilization. The most destabilizing effect was observed especially when the -OH group located at the ortho-position of the aromatic ring in the fragment -N=CH-Ar. For most of the substituted NBA molecules, it was the destabilized a framework that determined the destabilizing feature of the vertical resonance energy, instead of the stabilized n system. When the -NO2 substituent at the para-position of the aromatic ring of the -N=CH-Ar group, the π system had the highest stabilizing effect while the σ framework exhibited the highest destabilizing effect. While the -NO2 substituent was at the para-position of the left aromatic ring （At-）, the NBA had the least vertical resonance energy value.

Substituent Effect on N-Benzylideneanilines by DFT Energy Partition

To investigate the substituent effect on π‐electron delocalization of the N‐benzylideneaniline (NBA), the vertical resonance energies ΔE^V(θ) of eleven substituted NBAs were separated into π and σ parts at the B3LYP/6‐311G(d) level of the Density Functional Theory (DFT). When substituted with an electron‐releasing group –OH, the calculated ΔE^V(θ) of NBA was increased, indicative of more resonance destabilization than the mother molecule. However, when substituted with an electron‐withdrawing group –NO₂, the calculated ΔE^V(θ) values indicated less resonance destabilization. The most destabilizing effect was observed especially when the –OH group located at the ortho‐position of the aromatic ring in the fragment –N?CH–Ar. For most of the substituted NBA molecules, it was the destabilized σ framework that determined the destabilizing feature of the vertical resonance energy, instead of the stabilized π system. When the –NO₂ substituent at the para‐position of the aromatic ring of the –N?CH–Ar group, the π system had the highest stabilizing effect while the ( framework exhibited the highest destabilizing effect. While the –NO₂ substituent was at the para‐position of the left aromatic ring (Ar–), the NBA had the least vertical resonance energy value.