Structural isomer differentiation of 1,6-diaza-3,8-dioxabicyclo[4.4.1]undecane and N,N'-methylenebis(oxazolidine) by mass spectrometry

The title compound types are structural isomers. The absence of literature studies dealing with the mass spectrometric gas-phase behavior of such compounds prompted a search for the best conditions for differentiation between the two prototype examples (R,R)-5,10-diphenyl-1,6-diaza-3,8-dioxabi-cyclo4.4.1]undecane and N,N'-methylenebis(R)-4-phenyloxazolidine]. Attempts to differentiate between the isomers by NMR were inconclusive and X-ray crystallography had to be used. The best mass spectrometric results were obtained using gas-phase ionization techniques, particularly chemical ionization, whereby protonated molecules were observed. The fragmentation pathways were elucidated from MS/MS studies and from experiments performed on hexadeuterated samples of each compound.