The dependence of electron-transfer rates on the number of intervening groups is treated by using a single calculational method for four separate series of compounds: a biphenylyl donor and a 2-naphthyl acceptor, separated by various rigid saturated hydrocarbon bridges, a dimethoxynaphthyl donor and a dicyanovinyl acceptor, separated by norbornyl groups, a Ru(NH3)5II donor and a Ru(NH3)5III acceptor, separated by different numbers of dithiaspiro rings, and an Os(NH3)5II donor and an Ru(NH3)5III acceptor separated by an isonicotinyl plus a variable number of proline groups, which again provide a rigid spacer. The results for the electron-transfer matrix element obtained both with direct diagonalization and with the partitioning method are compared with each other, with the experimental results and, where available, with previously calculated results. © 1990 American Chemical Society.