Abstract Raman spectra of aqueous solutions of some silver-olefin complexes and the i.r spectrum of a new platinum-olefin complex, [PtCl 2 (Me 2 CCMe 2 )] 2 , have been studied in an attempt to enlarge upon a recent suggestion that v CC in platinum-olefin complexes could be preferably assigned to a Raman band in the 1240 cm −1 region rather than at about 1500 cm −1 . We conclude that while it is possible to assign the 1240 cm −1 band in the platinum-ethylene complex to a mainly CC stretching vibration in the complexes with substituted olefins the 1500 cm −1 band should be assigned to a mainly CC stretching mode. However both these statements are over simplications, and the true situation is best discussed in terms of the percentage charge of each frequency on complex formation. The summed percentage charges give the best spectroscopic measure of the modification of the CC bond.