Infrared Dichroism and Molecular Orientation of Ethyl 2-Hydroxyimino-3-oxo-3-phenylpropionate in Thin Films on Pd Metal Surfaces

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Abstract
The infrared absorption spectra of ethyl 2-hydroxyimino-3-oxo-3-phenylpropionate, in differently oriented films, formed on Pd metal plates, were measured by using the high-sensitivity reflection method. The thin crystal film A was formed when the solvent was evaporated from the thin liquid film remaining on Pd. On the other hand, the film B resulted from the crystallization of the amorphous solid film which was initially formed on Pd when the liquid film was thick. From the infrared dichroism in the reflection spectra, the molecular orientations in thin films were obtained as follows. In the film A, the ketone C=O and C=N bonds are probably at a pseudo s-cis and are aligned in such a way that the C–C bond connecting the ketone carbonyl group with the C=N group are nearly parallel to the Pd surface. The NO bond is aligned parallel to the metal surface. The ester group is oriented nearly vertical to the metal surface, the C=O bond lying tilted to the surface. In the film B, the ester C=O and NO bonds are aligned nearly perpendicular to the Pd surface, while the ketone C=O bond is not so. The C···C axis of the ester is rather parallel to the surface. The orientation in the thin film A agrees well with the hypothetical chelation model.

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