Stable Ylides H2CC1H, H2CFH, H2COH2, and H2CNH3 Studied by Neutralization-Reionization Mass Spectrometry

摘要

Contrary to the predictions of ab initio theory, the neutral ylides H2CC1H (1), H2CC1H, and H2CFH, as well as H2CNH3, exist in local energy minima. These have been prepared for study from fast gaseous H2CYH+ ions by neutralization with Mercury vapor. Reionization of the resulting fast neutrals produces abundant molecular ions, which could represent H2CYH(+) or H3CY(+) from partial or complete isomerization of H2CYH to the more stable isomer H3CY to the more stable isomer H3CY. However, increasing the pressure of the reionizing collision gas oxygen or helium increases the relative abundance of YH dissociation products, such as Hydrochloric acid from 1, which must originate from H2CYH, not H3CY. Thus an appreciable fraction of each of these neutral ylides must have survived for the microsecond lifetime of the experiment. For 1 this was confirmed by reionization to H2CC1H2(+), which shows a significantly different fragmentation pattern from that obtained from H3CC1. More than half of 1 molecules formed by vertical neutralization are still undissociated after .00001s, and of these less than half have isomerized to H3CC1. It appears that theory overestimates the heat-of-formation values for such hypervalent neutral species.