Abstract: There are a lot of studies on the stereochemistry of cyclic glycols by means of mass spectrometry, but the studies on the relative configurations of acyclic glycols by MShave not been found in literatures. This paper presents that the relative configurations of some acyclic glycols were firstly determined by Reaction Mass Spectrometry (RMS) using trimethyl borate as reagent. In five pairs of three- and erythro-isomers studied, there are no characteristic differences between their routine chemical ionization mass spectra. But in their reaction mass spectra, the relative abundance ratio, r, of characteristic ion, [Ms+M_R+H- 2CH₃OH]⁺, to reference ion, [M_s+H-H₂O]⁺, produced by the glycols of threo-configuration was much greater than that produced by erythro-isomers. Based upon this fact, we can distinguish the relative configurations between a pair of stereoisomeric acyclic glycols. And these phenomena were explained in virtue of the principles of stereochemistry.

Key words: Reaction mass spectrometry (RMS), Natural products, Threo-and erythro-isomers configurations