DFT guided substitution effect on azomethine reactive center in newly synthesized Schiff base aromatic scaffolds; syntheses, characterization, single crystal XRD, Hirshfeld surface and crystal void analyses

This paper aims to unfold the effect of substitution (ring A & B) on reactivity of newly synthesized crystalline azomethine linked aromatic compounds/Schiff bases (3a-c). Condensation reaction between 2-iodo-4-chloro substituted aniline with various suitably substituted aromatic aldehydes under acidic cat-alyzed reaction conditions gave crystalline compounds (3a-c) in good yields. The synthesized compounds were initially investigated in the solid state by single crystal X-ray crystallography besides other struc-tural characterizations. Possible reactivity of azomethine pharmacophore is explained based on the elec-tronic features of attached substituents on the aromatic rings A and B. DFT calculations further backed up the reactivity profile translated for compounds (3a-c) based on electronic grounds, while mechanis-tic investigation for further chemical reactivity is unfolded via frontier molecular orbital calculations and transition state predictions. Prominent nucleophilic character based on DFT study has been attributed to the halo i,e.,-Cl and-I substituents on aromatic ring (ring A) in all the synthesized derivatives (3a-c) with pronounced effect in 3c due to added nucleophilic behavior depicted by cyano substitution in ring B. However, HOMO orbital energy values for (3a-c) predict electron donor behavior of substituents (-CH3,-N(CH3)2,-C = N) on ring B with higher donation capacity predicted for 3b, thus indicating its oxidation in possible chemical transformations. Hirshfeld surface analysis revealed the prevalence of potential van der Waals interactions and hydrogen bonding as major intermolecular interactions in their (3a-c) crystal packings. In addition, crystal void analyses depicted high mechanical stabilities for (3a-c) due to absence of large cavities in their crystal packings. Moreover, reaction scope guided by the joint DFT and electronic explanations for the effect of substituents used on azomethine linkage has also been proposed/predicted as part of the study.(c) 2022 Elsevier B.V. All rights reserved.

Automated summary

This study aims to investigate the effect of substitution on the reactivity of newly synthesized crystalline azomethine linked aromatic compounds/Schiff bases. Crystalline compounds were obtained in good yields through condensation reaction between 2-iodo-4-chloro substituted aniline and suitably substituted aromatic aldehydes. The reactivity of the azomethine pharmacophore was explained based on the electronic features of the attached substituents. DFT calculations and frontier molecular orbital calculations were used to support the reactivity profile and understand the mechanistic aspects.