STUDIES ON OXIME HYDROCHLORIDES .4. NUCLEAR MAGNETIC RESONANCE STUDIES OF STEREOCHEMISTRY OF2-SUBSTITUTED CYCLOHEXANONE OXIMES AND THEIR HYDROCHLORIDES . CONFORMATION CHANGE CAUSED BY PROTONATION AND HYDROGEN BONDING

The configuration and conformation of 2-substituted cyclohexanone oximes and their hydrochlorides are investigated by means of ir and nmr spectroscopy. They include the compounds with substituents, OMe (I), OEt (II), Cl (III), Me (IV), OH (V), OCOCH3 (VI), OCOPh (VII), piperidinyl (VIII), and morpholinyl (IX). The E isomer is predominant in compounds IV, V, VIII, and IX, whereas less than 20% of the Z isomer appears in the rest. In all the compounds except IV and V, the substituent is axially oriented. The substituent of V is held in the equatorial position in nonpolar solvents by the intramolecular hydrogen bond formed between the nitrogen atom of the hydroxyimino group and the hydroxyl substituent. No other type of intramolecular hydrogen bond is observed. The presence of. the hydrogen bond is confirmed by the low wave-number shift in OH-stretching frequency under extremely dilute conditions. In V, the substituent shows an axial preference in polar solvents. A variation of the conformation and configuration is observed in some hydrochlorides. In the hydrochloride of IV the substituent turns to the axial position and, at the same time, the Z isomer appears because of the conversion from the E isomer. The substituents are partly equatorial in the hydrochloride of I, II, and III in the E isomer, while no appreciable change is observed in the Z isomer. This conformation change is interpreted in terms of electrostatic attraction between the lone-pair electrons of the substituent and the positive charge on the nitrogen atom due to the formation of the hydrochloride. The downfield shift of methyl signals is discussed in terms of the excess dipole moment of the nitrogen atom. © 1969, American Chemical Society. All rights reserved.