NJ(SI-29-C-13) COUPLING-CONSTANTS AND C-13, C-12 ISOTOPE SHIFTS IN SI-29 NMR-SPECTRA OF ETHYNYLSILANES

The coupling constants nJ(29Si13C) and isotope shifts nΔ29Si(13/12C) in the 29Si NMR spectra of the ethynylsilanes (CH3)3SiCCX (X = H, Br, I, SCH3, SC2H5, SC6F5, CH3, CH2Cl, CH2OC2H5, CH2N(C2H5)2, CH2Si(CH3)3, CH2Ge(CH3)3, CH2C(CH3)3, CF3, CN, C6H5, C6F5, Si(CH3)3, Ge(CH3)3, Ge(C2H5)3, Sn(CH3)3, Sn(t-C4H9)3) have been examined. There is a linear correlation between the isotope shifts and coupling constants. Compounds with X = MR3 (M = Si, Ge, Sn; R = Alk) deviate from these correlations, probably because the concurrent hyperconjugation falls in the order M = Sn > Ge > Si. The data are compared with the 119Sn NMR spectral data of the isostructural ethynylstannanes. © 1990.