Branched hydrogen-bond motifs as quantitative signatures of the structure and dynamics of liquid alcohols

Abstract

Hydrogen-bond (H-bond) networks dictate the self-assembly, dynamics, and macroscopic behavior of hydroxyl-containing liquids, yet their molecular determinants remain poorly defined. Here, we identify branched O2H1 centers (hydroxyl sites accepting two and donating one H-bonds) as key structural motifs that define H-bond network diversity in alcohols. Near-infrared spectroscopy, supported by theoretical analysis, quantitatively distinguishes OH species in three hexanol isomers, revealing characteristic O2H1 absorptions near 6250 cm−1. Molecular dynamics simulations link the O2H1 content to network topology and reorientation dynamics, where linear 1-hexanol forms disordered, flexible networks rich in O2H1 centers (12%), whereas 3-hexanol, with fewer O2H1 sites (4%), exhibits ordered, chain-like networks with longer H-bond lifetimes. The O2H1 fraction also modulates CuCl2 solubility and ion transport, establishing a direct molecular-level connection between H-bond motifs and the macroscopic functionality of alcohol-included liquids.