Dependence of Vicinal 31P-31P and 31P-13C Coupling Constants on the Dihedral Angle of α,β-Diphosphonates

Article abstract of DOI:10.1002/mrc.1260280606

Several α,β-diphosphonates with a norbornane or cyclohexane skeleton were prepared, and the 31P-31P coupling constants over three bonds for the ethyl or methyl esters, the acid and anion were obtained from the 13C NMR spectra or the 13C satellites in the 31P NMR spectra.The ³J(PP) values cover a range of about 90 Hz and are therefore well suited for conformational and configurational analysis.The dependence of ³J(PP) on the dihedral angle is well reflected by an extended Karplus relationship: ³J(PP) = A + B cos φ + C cos 2φ + D cos 3φ, with different parameters for the esters, acids and anions.For trans and gauche arrangements of the α,β-diphosphonic acids the dependence of the P-P coupling constants on the degree of titration is given.Investigations of the dependence of ³J(PC) on the PCCC dihedral angle show that a good curve fitting is achieved using the Karplus relationship ³J(PC) = A + B cos φ + C cos 2φ.A comparison of these curves with published data indicates smaller coupling constants for φ ca. 0 deg.The coefficients of the Karplus equation for the ³J(PC) values obtained for the esters are similar for acids and anions.