Theoretical study on the anomeric effect in carbene compound XC:CH2F (XÂ =Â CH3, NH2, OH)

Ab initio calculations up to MP2/aug-cc-pVTZ level have been carried out to study the anomeric effect in carbene compound XC:CH2F (X = CH3, NH2, OH, respectively) of singlet state and triplet state. For comparison, we also investigate the anomeric effect in XOCH2F (X = CH3, NH2, OH, respectively) of singlet state and triplet state. The calculations indicate that the gauche conformers are more stable in every case than that of the corresponding anti conformers. We suggest that the five-membered intramolecular C(N,O)-H…F hydrogen bonds play an important role in stabilizing the gauche conformation of these compounds. The negative hyperconjugation between the carbene lone pair and the anti-bonding C2-F orbital (lp(C:) → σ∗(C2-F)) results in stabilization of the antiperiplanar orientation of the C2-F bond relative to the carbene lone pair. In the singlet state of XC:CH2F, σ∗(C2-F) is well correlated with C1-C2 and C2-F bond length due to anomeric effect.