Theoretical study of the 1J(13C13C) indirect nuclear spin-spin coupling constant of the bridgehead bond in [1.1.1]propellane and related systems

Ab initio calculations using the equations of motion approach are reported for 1 J ( 13 C 13 C) of the bridgehead bond in [1.1.1]-, [2.1.1]-, [2.2.1]-, [2.2.2]-, [3.2.1]-propellane, bicyclobutane, bicyclopentane, bicyclohexane and tetracyclopentane. The results give an overall picture of the influences exerted on sign and magnitude of 1 J ( 13 C 13 C) by progressive condensation of the cyclobutane frame and by enlargement of the fused rings. Extraordinarily small values are predicted for [1.1.1]- propellane and [2.1.1]-propellane.