Computational Rationalization for the Observed Ground-State Multiplicities of Fluorinated Acylnitrenes

Computational methods are used to investigate the mechanism by which fluorination of acetylnitrene reduces the stabilization of the singlet configuration. Delta E-ST is made more positive (favoring the triplet state) by 1.9, 1.3, and 0.7 kcal/mol by the addition of the first, second, and third fluorine, respectively, at the CR-CC(2,3)/6-311(3df,2p)//B3LYP/6-31G(d,p) level of theory. Smaller effects observed with substitution of beta-fluorines in propanoylnitrene derivatives and examination of molecular geometries and orbitals demonstrate that the effect is due to inductive electron withdrawal by the fluorines, rather than hyperconjugation.