Triphenylphosphoniomethanide and alkyl-substituted analogs are torsionally unrestricted even at -100 Deg whereas the temp. dependence of the rotation around the Ca, Ph axis in triphenylphosphoniophenylmethanide reveals this ylide to be resonance stabilized to the extent of 8.5 kcal/mol. [on SciFinder (R)]
Nicola Marzari, Oliviero Andreussi
Rainer Beck, Ana Gutiérrez González, Fleming Crim