nbo analysis and density functional theory (dft: b3lyp/6-311+g**) based method were used to study the impacts of the anomeric effects (ae) on the conformational properties of 2-methoxy-1,2,4,5-tetrahydro-benzo[d]oxepine (1), -thiepine (2) and -selenepine (3). the gibbs free energy difference (geq–gax) values (i.e. δgeq-ax) at 298.15 k and 1 atm between the axial and equatorial conformations inc...