Oximes of azolecarbaldehydes and ?2-azoline-carbaldehydes and their derivatives

Abstract

The configurational (kinetic) stability of the anionic and zwitterionic forms of 1-methylpyrazolecarbaldehyde oximes and 1-methylimidazolecarbaldehyde oximes and their quaternary ammonium derivatives in aqueous solutions has been established. In an acid medium, isomerization takes place and an E-Z equilibrium of the cations of the oximes is established. The changes in the relative thermodynamic stabilities of the stereoisomers of the heteroaromatic carbaldehyde oximes as functions of the size and nature of the ring, the position of the oxime group, and the steric loading are due to spatial factors and electrostatic interactions. To substantiate the preferred conformations of the Z aldehyde oximes the differences in the values of the chemical shifts of the α protons of the ring and the rates of their deuterium exchange have been used.