Mass Spectrum, Mechanism and Structure in the Ion Chemistry of Trimethylmethylenephosphorane

Abstract

The gas phase ion chemistry of the simplest known phosphorus ylide, trimethylmethylenephosphorane, has been studied in the mass range m/e=2 - 186 and the pressure range 10-7-10-4 Torr. The most abundant product ion, m/e = 104, (CH3)2C2H5PCH2 '+ is formed by a methylene group transfer reaction of the molecular ion. Almost all of the other product ions formed from the molecular ion can be subsumed under the general formula (CH3)3PCHPRn + (R = H, CH3; n=1,2,3). The reactions indicate that the molecular ion has lost its ylide character almost completely. The protonated molecule is formed almost exclusively by a reaction of the fragment ion m/e = 75. This reaction and the CH3PH group transfer reaction indicate a cyclic structure (CH3) HP(CH2)2 + for this ion. A cyclic structure is also assumed for the ion m/e = 73, PC3H6 +, which undergoes P and PH transfer reactions. The reactions of the ion m/e = 47 are consistent with the structure CH3PH+. The ICR and mass spectra are given, some metastable decompositions are discussed