Study of base hydrogen bond in N,2,6-trichloro-p-benzoquinone imine with nuclear magnetic resonance and infrared spectroscopy. The assignment of syn and anti proton signals in the chloroimino group

The nuclear magnetic resonance (n.m.r.) spectra of N,2,6-trichloro-p-benzoquinone imine (1) and the anisotropy effect of the chloroimino group are investigated. A comparison of the n.m.r. spectra of 1 with those of oximes with a similar structure shows that the extent of the anisotropy effect is the same for both the chloroimino and the hydroxyimino group. This is also confirmed by comparison of N-chlorocyclohexanimine with cyclohexanone oxime. A downfield shift of the C—H proton signal in solvents acting as a base is observed, which is interpreted in terms of a [Formula: see text] base hydrogen bond. The extent of the shift is different between syn and anti sides and this gives the definite assignment for these two types of proton signals. Namely, the high-field signal, the extent of the downfield shift being larger, is assigned to anti protons, and the low-field one to syn protons. This assignment is extended to oximes owing to the equality of the anisotropy effects of the hydroxyimino and the chloroimino group. The formation of the [Formula: see text] base hydrogen bond is confirmed by the infrared (i.r.) spectra, and the correlation between the extents of n.m.r. downfield shift and i.r. low wave number shift is discussed. Furthermore it is found that the behavior of benzene molecule as solvent is different between the chloroimino and the hydroxyimino compounds.