The Prototypical Organophosphorus Ylidion ^•CH₂PH₃⁺

Abstract

The reactivity of the prototypical phosphorus-containing ylidion (α-distonic ion) •CH2PH3 + has been investigated in the gas phase by using a dual cell Fourier-transform ion cyclotron resonance mass spectrometer. The ion •CH2PH3 + and its more stable conventional isomer CH3PH2 •+ show distinctly different reactivities toward neutral reagents. This observation contrasts the facile interconversion of the analogous sulfur- and oxygen-containing distonic ions •CH2SH2 + and •CH2OH2 + with their conventional isomers CH3OH•+ and CH3SH•+, respectively, within collision complexes in the gas phase. Bracketing experiments yield a proton affinity of 190.4 ± 3 kcal mol-1 for the phosphorus atom in •CH2PH2. Together with a calculated heat of formation for •CH2PH2, this value yields a heat of formation of 217 ± 3 kcal mol-1 (at 298 K) for the distonic ion •CH2PH3 +.

Rearrangement and Fragmentation Processes on the Potential Energy Surfaces of the (CHnS)+ (n = 1−4) Systems

“…The most important result is perhaps the fact that both the doublet and quartet PES's are well separated from each other. As observed by Radom et al, on the doublet PES, the conventional isomer CH 3 SH + ( 1 ) was found to be energetically more stable than the ylide ion ( 2 ) by 21.9 kcal/mol. The ylide ion has two C s structures which are energetically close to each other (0.2 kJ mol -1 ) with the anti conformation being more favored over the syn.…”

“…For this reason, we choose the same level of theory for the full characterization of the various PES's of (CH n S) + ( n = 1−4) ions. The experimental investigations and most of the theoretical studies , on CH 4 S + are restricted largely to thermochemical data. Radom et al, 20c,d in their earlier investigation on the doublet potential energy surface of the CH 4 S + system at the MP3/6-31G**//6-31G* level, have identified transition states for three reaction channels viz., CH 3 SH + → CH 2 SH 2 + , CH 3 SH + → CH 2 SH + + H • , and CH 2 SH 2 + → CH 2 SH + + H • .…”

“…The (CH 3 S) + system has been the subject of several theoretical studies in a different context. 20c,− Most of these deal with the thermochemistry and proton affinity of these molecular ions. Collisional activation mass spectra 15 suggest the protonated thioformaldehyde, H 2 CSH + to be more stable compared to the thiomethoxy CH 3 S + structure.…”

Distinguishing conventional and distonic radical cations by using dimethyl diselenide

“…Furthermore, the aromatic distonic ions N..(3-dehydrophenyl)-3 -fluoropyridinium ion (Figure Ia) and 4-dehydrophenyldimethyl sulfonium ion react with CH 3SeSeCH3 by CH 3Se ' abstraction approximately three times faster than they react with CH 3SSCH3 (the reaction efficiencies are 25 and 14% versus 7 and 5%, respectively; Table 1). Similarly, the prototypical organophosphorus distonic ion 'CH z PH j reacts with CH 3SeSeCH3 by exclusive CH 3Se' abstraction at 75% of the collision rate (Figure 1c; Table 1), whereas the reaction with CH 3SSCH3 yields both the electron transfer and CH 3S ' abstraction products (at 40% of the collision rate) [13].…”

“…The facile CH 3Se ' abstraction observed for distonic ions can be used to distinguish them from their conventional isomers. For example, while the ion 'CH zPH j reacts with CH 3SeSeCH3 by CH 3Se' abstraction, its conventional isomer CH 3PHi" yields only the electron transfer product (Table 2) [13]. Similarly, electron transfer is the only reaction observed for the conventional radical cation of trimethylene oxide, while its ring-opened distonic form 'CH zCH zOCH~yields several products, including that formed by CH 3Se ' abstraction (Tables 1 and 2).…”