Experimental and quantum chemical investigation of the stereochemical dependence of spin coupling constants in symmetrical strained alkenes

The 13C–13C, 13C–1H and 1H–1H spin coupling constants in some strained symmetrical alkenes were measured using a new gradient selected method. The olefinic 1J(C,C) spin coupling constants were calculated using ab initio and DFT quantum chemical calculations for model compounds. The calculated and experimental data are in good agreement. The olefinic 1J(C,C) spin coupling constants do not reflect the high distortion of the double bond in silacycloheptene 2. This is attributed to the fact that the Fermi contact contribution to the coupling constants is transmitted via the sp2-type σ-orbital, whereas the π-type MO with a nodal plane at the position of the nuclei does not contribute to the 13C–13C coupling.