2‐(Hydroxyimino)aldehydes: photochemical and physico‐chemical properties of a versatile functional group for monomer design

In the context of our research on stimuli-responsive polymers bearing the 2-(hydroxyimino)aldehyde (HIA) 2 group, we explore the photochemical behavior and physico-chemical properties of a number of HIAs. Interpretation of experimental data is supported by quantum mechanical calculations. HIAs are expected to undergo photoisomerization, chelate metal ions, yield hydrogen-bonded dimers or oligomers, exhibit relatively low pKas, and form >C=NO• radicals through OH hydrogen abstraction or oxidation of the oximate ion. Besides the well-established E/Z oxime photoisomerism, we observe a Norrish-Yang cyclization resulting in cyclobutanol oximes, to our knowledge not described in previous literature. Acidity, Bond Dissociation Enthalpies and electrochemical properties of HIAs are compared to literature data on simple oximes. Results are discussed in relation to the many potential applications for HIAs, with emphasis on the synthesis of novel HIA-containing responsive polymers.