Low-temperature F NMR spectroscopy of 1-fluoro-1-lithioethenes : Stability, shifts and unexpected coupling constants

Half-lives and fluorine atom shifts of stabilized 1-fluoro-1-lithioethenes bearing hydrogen, fluorine, phenyl, and/or dimethylphenylsilyl groups in the β-positions have been determined by a low-temperature ¹⁹F NMR spectroscopy. Some 1-fluoro-1-lithioethenes displayed an exceptionally low value of the trans-³J_FF coupling constant. Stereoselectivity of carbenoid formation, as well as an effect of configuration on the stability is discussed.