Carbon-13 and phosphorus-31 nuclear magnetic resonance spectra of some symmetrical long chain ditertiary phosphines and the carbon-13 nuclear magnetic resonance spectra of the arsenic analogues

Abstract

The proton noise decoupled pulsed Fourier transform ¹³C n.m.r. spectra of the long chain ditertiary phosphines and arsines of the general formula Ph₂E[CH₂]_nEPh₂(E = P and As, n= 6–12 and 16) have been examined. The range of significant carbon–phosphorus coupling in the phosphines studied is limited to a maximum of three bonds. The method for assigning each of the individual ¹³C resonances is discussed and the assignments are contrasted with those obtained for the corresponding linear alkanes. Systematic trends in the chemical shift parameter are observed and are explained in terms of the effect of the presence of phosphorus or arsenic atoms at both ends of the alkane chain. The ³¹P n.m.r. spectra of the phosphines have also been recorded. The correlation between the ³¹P chemical shift and the effective steric bulk of the polymethylene backbone has been examined for those ligands and compared to values reported for similar ditertiary phosphines with fewer methylene units present between the phosphorus atoms.