ELECTRON INFLUENCE OF SUBSTITUENTS CONTAINING TRIVALENT PHOSPHORUS

The groups containing trivalent phosphorous belong to the second-kind substituents although they possess a lone electron pair. β-Orientation of piperidine addition to vinyl-PIII-compounds, ionization constants of phosphorus-substituted benzoic acids or phenols as well as protophylic hydrogen exchange reaction in tertiary phosphines are all indicative of this fact. We determined the σ-Hammett- and σ-constants and calculated σI- and σR-constants for Ph2P-, Ph2P(O)-, Ph2(S)- and Ph2N-groups. The results show either no or minor ρ{variant}-π-conjugation effect and the presence of acceptor conjugation. The lone electron pair of trivalent phosphorus displays a weaker ρ{variant}-π-conjugation than those of other third period elements. The reason for this may possibly be an increased s-character on a lone pair of phosphorus electrons, which agrees with the values of valence angles in PIII-compounds. © 1969.