Ab initio modelling of the anomeric and exo anomeric effects in 2-methoxytetrahydropyran and 2-methoxythiane corrected for intramolecular BSSE.Accurate ab initio calculations including basis set limit (BSL) extrapolations, removal of intramolecular basis set superposition error (BSSE), solvent effect corrections, and thermal effects have been carried out to compare the structure and the anomeric and exo-anomeric effect in 2-methoxytetrahydropyran and 2-methoxythiane. 
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