The electronic and molecular structure of 2,6-bis{N-(2-hydroxyphenyl)iminomethyl}-4- methylphenol (hpimp) is clarified from the measurements of electronic absorption and 1H NMR spectra in various solvents and an X-ray diffraction analysis, together with MO calculations. Electronic absorption bands of hpimp are at 422, 397.9, 359, 341, 294.3, 265.8, and 224 nm in the non-polar solvent cyclohexane. In polar solvents, such as methanol, an additional band which is assigned to a partly formed keto-amine hpimp, is observed at 499 nm. From the 1H NMR spectra it is seen that hpimp exists in the enol-imine form in non-polar solvents, and as an equilibrium mixture of enol-imine and keto-amine forms in polar solvents. Each electronic absorption band of solid hpimp in a KBr disk is broadened compared with the solution state, and an additional band, again assigned to the keto-amine form, appears around 499 nm. An X-ray diffraction analysis shows that hpimp assumes a keto-amine structure in the solid state, and forms a column structure along the c-axis. MO calculations suggest that the enol-imine hpimp has a twist structure around the two C−C single bonds, the twist angle being 100° to 120°.
X-ray diffraction analysis of butyl- and isobornyl acrylate/heptakis(2,6-di-O-methyl)-β-cyclodextrin complexes and correlation to 1H NMR-spectra
