Distinguishing Aromaticity from Antiaromaticity with Information-Theoretic and Energetic Information Quantities and...

Aromaticity and antiaromaticity are foundational concepts in chemistry, yet their precise classification, differentiation, and quantification remain the subject of ongoing debate in the literature. In this work, we systematically investigate aromaticity and antiaromaticity patterns for a series of substituted fulvene derivatives in both lowest singlet and triplet states and then cross-correlate their numerical results from the information-theoretic approach (ITA), energetic information, topological analysis, and molecular properties (e.g., atomic polarizability, C₆ dispersion coefficient, Hirshfeld charge, and electron density) with different aromaticity indexes (e.g., NICS(0), NICS(1), FLU, HOMA, and HOMER). Our cross-correlation results reveal that aromatic and antiaromatic systems exhibit completely opposite patterns in each of the spin states. In addition to ITA quantities previously identified that can be employed to distinguish aromaticity from antiaromaticity, newly introduced energetic information, and the topological analysis of ITA quantities also verify this regularity. Notably, the same opposite behavior between aromaticity and antiaromaticity is also observed for atomic polarizability, C₆ dispersion coefficient, Hirshfeld charge, and electron density, uncovering the intrinsic connections between electron delocalization and molecular response properties. Furthermore, the four properties demonstrate strong linear correlations with the ITA and energetic information quantities. This study should have provided new qualitative and quantitative perspectives and insights into understanding aromatic and antiaromatic propensities of molecular systems.