STEREOSELECTIVE CHEMICAL-IONIZATION MASS-SPECTROMETRY - REACTIONS OF CH3OPOCH3+ WITH CYCLIC VICINAL DIOLS

The phosphenium ion CH3OPOCH3+ readily attacks hydroxyl groups of neut ral substrates in the gas phase in a Fourier-transform ion cyclotron r esonance mass spectrometer. The electrophilic character of CH3OPOCH3is in agreement with molecular orbital calculations (Becke3LYP/6-31G(d ) + ZPE) that predict a singlet electronic ground state for this speci es. The observed reactions provide a convenient synthetic route to var ious larger phosphenium ions in the gas phase. Most importantly, howev er, CH3OPOCH3+ was found to be extremely sensitive to the stereochemic al structure of the neutral substrate. The dramatically different reac tion product distributions obtained for diastereomeric cyclic vicinal diols suggest that CH3OPOCH3+ provides a powerful chemical ionization reagent for the mass spectrometric determination of the stereochemistr y of diols.