Differentiation of isomeric camphane-2,3-diols by NMR spectroscopy and chemical ionization mass spectrometry

Abstract

Four diastereoisomeric camphane-2,3-diols have been synthesized and their structures verified by 13H and 13C NMR spectroscopy. Mass spectrometric differentiation of these compounds was difficult by conventional methods: the electron ionization mass spectra were almost identical, stereochemical effects were weak when NH3 and i-C4H10 were used as reagent gases in chemical ionization, and the differences apparent in the CH4 chemical ionization spectra were not easily related to the stereochemistry. Stereochemical effects were clear, however, in the collision-induced dissociation spectra of the ammonium adduct (M+ NH4)+ in which ions and isomers were easily differentiated. Under chemical ionization, oxidation and/or hydride-ion abstraction reactions took place, leading to products the structure of which strongly reflected the configuration of the original diol thereby offering a further means to isomeric identification.