The Molecular Structure of Allenes and Ketenes, XII [1] Four-Bond Proton-Proton Spin-Spin Couplings in Allenes

Allenes, Proton-Proton Coupling Constants, Substituent Effects Four-bond proton-proton coupling constants in allenes are reported. The substituent effects on the coupling constants are discussed on the basis of the dual-substituent parameter approach. Furthermore, the coupling constants are related to quantumchemical indices (electron densities, overlap populations) obtained from semiempirical CNDO/S and ab initio STO-3G calculations. The magnitudes of the coupling constants depend upon the polar natures of the substituents as well as upon their charge-transfer abilities (resonance effects) to a comparable amount. In general, the coupling constants in 1,3-disubstituted allenes are nonadditive in ligand specific parameters.