Linking geometric and electronic descriptors of aromaticity in cyclic hydrogen-bonded chains: a synergetic approach using the HOMIA and Q2 (descriptors)

The aromatic character of H-bonded systems is explored by comparing two new descriptors: The structural harmonic oscillator model of intermolecular aromaticity (HOMIA) and the Q 2 -based descriptors derived from the electric quadrupole Q 2 tensor components obtained from the distributed multipole analysis (DMA) expansion. When applying them to cyclic (HCN) n and (HNC) n chains, these descriptors reveal a polynomial relationship between geometric and electronic anisotropy, as characterized by each type of descriptor. The Q 2 , zz descriptor yields results consistent with a pseudo-π character, suggesting a potential out-of-plane delocalization analogous to π-systems, despite the presence of only σ-type H-bonds in the investigated systems. This cooperative delocalization shows that the HOMIA and Q 2 descriptors are sensitive tools for characterizing nonconventional aromaticity character in H-bonded rings.