The influence of hydrogen bond formation and the proton transfer on the structure of complexes of phenols with N-methylmorpholine

Structural and energetic consequences of forming the hydrogen bonded complexes between six selected phenols and N-methylmorpholine are discussed on the basis of results of B3LYP/6-31G(d,p) calculations. Dependences of various structural parameters on the degree of proton transfer were established. The progress of the proton transfer was characterized by the O-H (d(OH)) distance, d(CO) distance and XPT. The last one was derived from the dependence of calculated dipole moment on d(OH). It was established, that dependences received at use of d(OH) scale reveal the sigmoid character, while for d(CO) and XPT scales more linear dependences were found. Especially strong influence of substituents on the dependences on d(CO) was stated. The structures with the shortest hydrogen bonds, were characterized in detail, also with the use of the formulations going from the valence conservation rule in hydrogen bond. By comparison with our earlier results, the specific properties of such “critical” structures for the complexes with pyridine were pointed out. It can be treated as evidence on resonance interactions in hydrogen bond formed between aromatic acids and bases.