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

Electronic structure, charge distributions and vibrational characteristics of CH3O(CH2CH2O)(n)CH3 (n = 3 - 7) have been derived using the ab initio Hartree Fock and density functional calculations. For tri- to hexa-glymes 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 kJ mol(-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 transconformers. 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 similar to 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.