hybrid-dft study and nbo interpretations of conformational behaviors of 2-methoxy-1,2,4,5-tetrahydro-benzo[d]oxepine, -thiepine and -selenepine

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 increase from compound 1 to compound 2 but decrease from compound 2 to compound 3. the nbo analysis showed that the ae associated with donor-acceptor (lp→σ*) interactions increases from compound 1 to compound 2 but decreases from compound 2 to compound 3. also, the calculated dipole moment difference [δ(μeq - μax)] values between the axial and equatorial conformations increase from compound 1 to compound 2 but increase from compound 2 to compound 3. based on the results obtained, there is no conflict between the ae and the electrostatic interactions [i.e. δ(μeq - μax)] on the conformational behaviors of compounds 1-3.