In this study, we performed a combined density functional theory (DFT) and experimental investigation of the hydrogen bonding strength and thermodynamic properties in mixtures of o-toluidine and 1-alkanol (1-propanol to 1-hexanol). The DFT calculations were carried out using the M05-2X/6–311 + + G ∗ ∗ computational level to optimize the structures and calculate the hydrogen bonding energies. The experimental measurements were conducted using density and viscosity measurements to determine excess and deviation properties, and unraveling the strength of molecular interactions in the mixtures. The results showed that the hydrogen bonding strength and thermodynamic behavior of the mixtures were strongly influenced by the length of the alkyl chain in the 1-alkanol molecule. The DFT calculations revealed that the hydrogen bonding energies decreased with increasing alkyl chain length, while the experimental measurements showed that the excess molar volumes are increased and deviation in the viscosity are decreased. Overall, this study provides valuable insights into the interplay between hydrogen bonding and thermodynamics in o-toluidine and 1-alkanol mixtures and highlights the importance of combining DFT calculations and experimental measurements to understand complex intermolecular interactions
