Unravelling the non-covalent interactions in certain n-propyl amine – Ether systems through acoustic and DFT studies at 303.15 K

Ultrasonic study of four binary liquid mixtures, containing n-propyl amine (NPA) as the common component and four structurally different ethers [tetrahydrofuran (THF), 1, 4 dioxane (DIOX), anisole (ANI) and diphenyl ether (DPE)] as varying components is carried out over the entire mole fraction range at 303.15 K and at experimental pressure of 101 kPa. The acoustical and excess thermo acoustic parameters reveal the existence of H-bonded interactions in the four systems and the influence of non-covalent interactions on the constitutional arrangement of ether molecules. It is found that the H-bonded interactions with NPA are stronger in aromatic ethers (ANI, DPE) systems than those in alicyclic ethers systems (THF, DIOX), presented in the manuscript. The optimized molecular geometries of dimers of pure components and the amine-ether complexes are obtained through Density Functional Theory (DFT) method. The values of dipole moments and interaction energies reveal that the stabilization arises due to C-H---π, C-H---O and C-H---N non-covalent interactions (NCI) besides the classical N-H---O H-bonding. The independent gradient model (IGM) analysis of the four systems shows structural dependent on the strength of the interactions. δginter descriptors obtained from pro-molecular IGM method presented against sign(λ2)ρ show the variation of interaction energies of complexes of NPA with structure of ethers.