Nuclear magnetic resonance of organophosphorus compounds: Signs of long-range 1H 31P spin-spin coupling constants in tri-(5-methyl-2-furyl)-phosphine derivatives

Abstract

The magnitudes and relative signs of the long-range 1H 31P spin coupling constants between the side-chain protons and the 31P nucleus in tri-(5-methyl-2-furyl)-phosphine, its sulfide and methyl phosphonium salt have been obtained. The relative signs were deduced from homonuclear spin tickling and selective decoupling experiments. Upon tetracoordination of phosphorus a change in the sign for this long-range (five- and/or six-bond) coupling is observed. For the phosphine | J PCH 3 | = 0.19 Hz and has the same sign as the 1H 31P ring coupling constants ( 3 J PH(3) and 4 J PH(4)), i.e., positive, whereas for the phosphine sulfide and methyl phosphonium salt | J PCH 3 | equals 0.46 and 0.38 Hz, respectively, and are both of opposite sign to the 1H 31P ring couplings, i.e., negative.