Preparation and nuclear magnetic resonance study of phosphorus–fluorine compounds undergoing intramolecular exchange. Part 4. Rotameric forms of 1-piperidyltrifluorophosphoranes

Abstract

Fluorine-19 and phosphorus-31 n.m.r. spectra are reported at variable temperature under conditions of proton decoupling for four 1-piperidyltrifluorophosphoranes, substituted with a methyl group in the piperidyl ring so as to impart chirality. The axial fluorines are non-equivalent even at ambient probe temperature. As the temperature is lowered the spectrum shows evidence of two isomeric forms in each case, caused by the slowing of internal rotation about the P–N bond. The n.m.r. spectra were analysed to yield chemical shifts and coupling constants. The results are discussed in relation to conformation.