Heterogeneously substituted radicals and carbenes: photoelectron imaging of the FC(H)CN(-) and FCCN(-) anions.

This work represents the next step in the studies of heterogeneous substitution effects in cyanohalo radicals and carbenes. Negative-ion photoelectron imaging was used to investigate the substituted radical and carbene derivatives of fluoroacetonitrile. We report a closed-shell singlet ground state for cyanofluorocarbene, FCCN, with a directly measured adiabatic electron affinity EA = 2.081 ± 0.002 eV and a singlet-triplet gap of ΔE(S-T) = 0.42 ± 0.04 eV, estimated through a combination of experimental and theoretical results. The open-shell singlet (1)A″ state was also observed experimentally. The cyanofluoromethyl radical, FC(H)CN, was similarly estimated to have an EA of 1.53 ± 0.08 eV. This value was used to estimate the C-H bond dissociation energy (BDE) of fluoroacetonitrile, DH298 = 90.7 ± 2.8 kcal mol(-1). The results are discussed in comparison with results for other fluoro- and cyano-substituted radicals and carbenes, and in light of our recent work on the radical and carbene derivatives of chloroacetonitrile. The estimated ΔE(S-T) of FCCN agrees well with the general trend of similar carbenes. We also find that, similar to chloroacetonitrile, the low C-H BDE of fluoroaceotnitrile indicates a synergistic stabilization of the corresponding radical by a π donor (halogen) and π acceptor (CN).