Proton transfer complexes between phenols or tetrazole and 1,8-bis(dimethylamino)naphthalene. Non-ergodicity of the equilibria

Abstract

In solvents such as dichloroethane and acetonitrile, the “proton sponge” 1,8-bis(dimethylamino)naphthalene forms, with 3,5-Cl 2-phenol and tetrazole, proton transfer complexes containing several proton donor molecules. These complexes are already observed in a marked excess of the proton sponge. These proton transfer systems markedly deviate from the ergodic behaviour. The equilibrium is not ruled by the concentrations of the various entities in the ensemble, but by the fractions (1 − γ) and γ of the time during which the proton of the donor is involved or not involved in H-bonding, either with the sponge B or with the basic site of another AH molecule. An equation is derived according to the non-ergodic theory of the mobile order, which allows one to relate the concentration of the donor molecules having a free AH vibrator to the formal concentrations of the sponge and of the proton donor. This equation is based on a dynamic model of the complexes where, in excess of the donor, homoconjugated anions bonded to several donor molecules (AHAHAHAHA) − are formed. In these anions the formal negative charge jumps from one A entity to another one, provoking variations in the AH distances. Outside of the anion the protonated base BH + follows this jump, moving along the homoconjugated anion, the B +H·A − bond being formed at the place where the negative charge is temporarily located.