Influence of protonation on internal rotation of dimethyl ether

A model is proposed for the influence of protonation on ether potential surfaces. The model invokes the quantum-mechanical effect of protonation on the oxygen lone pair and its consequence on the internal rotation barriers and associated torsional rotation energy levels. The barrier reduction and lowered torsional energy gaps lead to possible conformational changes at ambient temperatures. The model is applied to dimethyl ether. In this case, the torsional fundamental energies become comparable to, or below, the room-temperature Boltzmann energy (depending on the proton position relative to the dimethyl ether lone pair), so that the geometry distribution in the protonated species is driven toward the asymmetric staggered-eclipsed conformer, rather than the highly preferred symmetric (C_2v) eclipsed-eclipsed conformer in dimethyl ether.