Difluorovinylidene, F_2C=C:

摘要

Vinylidenes R~1R~2C=C: rearrange so rapidly to alkynes R~1C≡CR~2, which are more stable by 35-45 kcalmol~(-1), that they could be detected directly only in few cases. The singlet carbenes H_2CC: and FHCC: were characterized in the gas phase by meansof the vibrational progression in the photoelec-tron (PE) spectra of the anions H_2CC~- and FHCC~-. The immediate rearrangement of 1-H-vinylidenes into alkynes by 1,2-H shift is rendered possible by a very low activation barrier calculated to be 2-4 kcalmol~(-1).