Stereoelectronic effects in negatively and positively (protonated) chargedspecies. Ab initio studies of the gauche effect in 1,4-dioxa systems

A computational study ab initio of the conformational dependence of proton affinities of 8-methoxyethoxide (MEO), dimethoxyethane (DME), and 1,4-dioxa ne has been carried out at the MP2/ 6-31+G* level of theory. The results we re discussed in comparison with reference systems, from simple alkoxides an d ethers to anomeric moieties, in open, cyclic, and bicyclic molecules. The COCCOC species are stronger bases than the COCOC (anomeric) ones and appro ach regular ethers in their strength. The gauche forms in MEO and DME are a ltogether stronger bases than the anti forms, and anti (equatorial) protona tion is preferred over gauche (axial), unless ditopic protonation is possib le, like in aga-DME or cis-tetraoxadecalin. The gauche effect plays a signi ficant role in the formation, relative stability, and reactivity of the cha rged species.