Ab initio HF/6-31G* calculations of O-vinylacetoxime monohydrates and catio
ns were performed. Each conformer forms two stable H-complexes with partici
pation of N and O atoms. The former have planar heavy-atom skeletons, where
as the water molecule in the latter is located above the plane of the proto
n-acceptor complex. The complexes stabilized by N...HO and O...HO bonds hav
e different dipole moments and frequencies of the OH stretching vibrations.
The most energetically favorable cation is formed by adding a proton to th
e C-beta atom of the vinyl group of O-vinylacetoxime. The ap,ap-conformer (
ap is antiperiplanar) of this cation is 6.5 and 34.9 kcal mol(-1) more stab
le than the onium cations with the NH+ and OH+ fragments, respectively, and
is characterized by polarization and appreciable lengthening of the N-O an
d C=C bonds.