Influence on the reactivity properties of the substitution by different halogens on the conjugated backbone of the 1,3,5-triaryl-2-pyrazoline skeleton in relation to the increasing alkyloxy chain length: a conceptual density functional theory study.

A series of non-substituted 1,3,5-triaryl-2-pyrazolines and pyrazolines substituted with Fluoro (-F), Chloro (-Cl) and Bromo (-Br) groups at the 3-aryl position were studied. All calculations were done using the conceptual framework of density functional theory. The geometries and reactivity properties were analyzed according to an increase from one to twelve alkyl units in the 5-aryl of 2-pyrazoline ring. In order to be able to apply the particular methodology named KID procedure (for Koopmans in DFT), the KID descriptors were calculated and the results showed that the use of this approximation (Koopmans' theorem in DFT studies) is feasible. The results for the geometries determined that the increase of the chain with alkyl units does not affect the geometry of the systems. However, the solvation energy also calculated is affected by this increase in the allyl chain length. Due to this, as the chains increases, the solubility of the molecular systems diminishes. The chemical reactivity properties were determined by calculating the descriptors that arise from conceptual DFT and it could be demonstrated that they are not affected by the chain growth. Slight differences were found due to the different halogen substitutions. Finally, it could be observed that all the pyrazolines present an important electrophilic behavior. Graphical Abstract Properties changes in relation to the increasing alkyloxy chain length and halogens presence.