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.