Refinement of molecular mechanics parameters for ethers based on the conformational energies of Me–O–X (X = Me, Et, Pri and But) obtained by ab initio molecular orbital calculations
The conformational energies of 13 conformers, including saddle points of internal rotation, of the title compounds were calculated by various levels of the ab initio molecular orbital method. The calculated conformational energies at MP4(SDQ)/6-31G*//HF/6-31G* were close to the experimental values, the only exception being the eclipsed barrier height of ethyl methyl ether. The conformational energies obtained by the Hartree–Fock method did not agree well with the experimental values. Molecular mechanics parameters for the ether molecules were refined to reproduce the calculated conformational energies at the MP4(SDQ)/6-31G*//HF/6-31G* level. The refinement of bending parameters was important to reproduce the calculated conformational energies, as well as the refinement of torsional parameters.