Evaluation of Slight Changes in Aromaticity through Electronic and Density Functional Reactivity Theory-Based Descriptors

Abstract

Aromaticity is a useful tool to rationalize the structure, stability, and reactivity in several compounds. Although aromaticity is not directly an observable, it is well accepted that electronic delocalization around the molecular ring is a key stabilizing feature of aromatic compounds. This contribution presents a systematic evaluation of the capability of delocalization and reactivity criteria to describe aromaticity in a set of fluorinated benzenes. The aromaticity indices are compared with quantities obtained from the magnetic criteria of aromaticity, i.e., the strength of the ring current induced by an external magnetic field and the popular NICS zz (1) index. In this evaluation, the indices based on delocalization criteria used are aromatic fluctuation index (FLU), para-delocalization index (PDI), PDI π , and the multicenter delocalization index (MCI). In addition, indices based on the bifurcation values of scalar functions are derived from electron density such as electron localization function (the π contribution, ELF π ) and the π contribution of the localized orbital locator (LOL π ). Furthermore, reactivity indices based on chemical reactivity and the information-theoretic (reactivity) approach are para-linear response (PLR), Shannon entropy, Fisher information, and Ghosh–Berkowitz–Parr (GBP) entropy. The results obtained show that the delocalization-based indicators present a high sensitivity to slight changes in aromaticity and that the reactivity criterion can be considered as a complementary tool for the study of this phenomenon, even when these changes are minimal. These results encourage the use of multiple indicators for a complete understanding of aromaticity in various chemical compounds.

Update for Isomerization Stabilization Energies: The Fulvenization Approach

“…The fulvenization process serves as a methodology for quantifying the aromaticity of the benzene derivatives. An example is found in the persubstituted benzenes when hydrogen atoms are replaced by fluorine atoms, which presents a reduction in its aromatic character (25.09 kcal·mol –1 ), in agreement with previous studies applying the magnetic criteria and information-theoretic-based indicators . A reduction in aromaticity is also observed when hydrogens are replaced by chlorine, cyano, and hydroxyls, whose values are 30.56, 26.20, and 26.18 kcal·mol –1 , respectively (Figure S1 in the Supporting Information) .…”

Self-assembled molecules as selective contacts in CsPbBr3 nanocrystal light emitting diodes

“…The addition of the second benzyl moiety in the linker section of the EADR04 molecule improves electron delocalization in the molecule, which in turn increases its electronic and thermal stability. 34,35…”

Exploring the supramolecular profile of 5-phenylhydantoins

“…Among numerous available descriptors, the nucleus-independent chemical shift (NICS(1) zz , NICS(1.5) zz ), 23 and para -delocalization index (PDI) 24 were selected to study the aromaticity of 5-phenylhydantoins (for more details see Computational details). Based on the results of a recent evaluation of aromaticity descriptors, 25 it was shown that these two descriptors have an excellent correlation with the ring current strength (RCS), value used as a referent. The applicability of the selected DFT method was tested on the benzene molecule, and the obtained values of PDI and NICS(1) zz are in excellent agreement with the literary ones.…”