Theoretical investigations on structure, electrostatics potentials and vibrational frequencies of Li+–CH3–O–(CH2–CH2–O)n–CH3(n = 3–7) conformers

Abstract

Electronic structure, charge distributions and vibrational characteristics of CH3 O(CH2 CH2 O)n CH3 (n=3-7) have been derived using the ab initio Hartree Fock and density functional calculations. For tri- to hexaglymes the lowest energy conformers have trans- conformation around the C-C and C-O bonds of the backbone. For heptaglyme (n=7 in the series), however, gauche-conformation around the C-C bonds renders more stability to the conformer and turns out to be 10.1 kJmol−1 lower in energy relative to the conformer having trans-orientation around the C-C and C-O bonds. The molecular electrostatic potential topographical investigations reveal deeper minima for the ether oxygen in conformers having the gauche conformation around the C-C bonds over those for the trans- conformers. A change from trans- to gauche-conformation around the C-C bonds of the lowest energy conformer of heptaglyme engenders a triplet of intense bands ∼1,150 cm−1 in the vibrational spectra. Theoretical calculations predict that Li+ binds strongly to the heptaglyme conformer in the above series. The frequency shifts in the vibrational spectra of CH3O(CH2CH2O)n CH3- Li+ (n=3-7) conformers have been discussed