Evaluating Stability of C8H15O-X (X: OH, NH2) Conformers by using NBO Analysis

In quantum chemistry, a natural bond orbital or NBO is a calculated bonding orbital with maximum electron density. NBOs are transformed molecular orbitals, calculated to provide the ideal Lewis structure of a molecule. In this work, we investigated anomeric effect in C8H15O-X (X: OH, NH2) by using NBO analysis. C8H15O-X (X: OH, NH2) can be two conformers, anti and gauche conformers of CO. The gauche conformer is preferred to the anti conformer by using anomeric effect. Theoretical calculations were carried out at the B3LYP/6-311+G** level to investigate conformational energy of a series of C8H15O-X(X=OH, NH2). According to our results, the Gibbs energy of the gauche conformers was lower than that of the corresponding anti conformers. The NBO analysis of donor- accepter interactions showed that the stabilization energies associated with LP2 X16→ π*C12-O15 delocalization electrons for the anti conformers increase from compound of C8H15O-OH to compound of C8H15O-NH2 and LP2 X15→ π*C12-O15 delocalization electrons for the gauche conformers is as the same way. These results showed increasing of electron delocalization from compound of C8H15O-OH to compound of C8H15O-NH2 and increasing of anomeric effect, so interactions between donor- acceptor orbitals increases and structures are stable.