Probing the Hidden Noncovalent Interactions between Ethers and Amines through Volumetric, Viscometric, Ultrasonic, IR Spectral, and DFT Methods

Extensive ultrasonic, volumetric, and viscometric investigations were conducted on four binary liquid mixtures containing two structurally different amines (n-hexyl amine (NHA) and cyclohexyl amine (CHA)) as hydrogen donors and two aryl ethers (anisole (ANIS) and diphenyl ether (DPE)) as hydrogen acceptors to probe the structural effect on the amine-ether molecular interactions. We report the measured speed of sound, density, and viscosity of liquid mixtures in the entire range of mole fraction. The trend in the acoustical and volumetric parameters for the four mixtures indicates that NHA systems show moderate interactions, while CHA systems show weak interactions. FTIR spectra of the mixtures establish the presence of a hydrogen bond between amine and ether. DFT study reveals the presence of various noncovalent interactions (NCI) through NCI and RDG plots, and the strength of interactions was compared using interaction energy. The interactions in DPE systems are weak due to steric interactions. The present work successfully correlates the results obtained on noncovalent interactions through DFT study and their influence on the bulk properties of liquid mixtures observed through acoustical study. These weak interactions identified are helpful in the choice of a suitable solvent with required solubility parameters in the synthetic organic and pharmaceutical industries.