The vibrational spectra of the metalloporphins: A normal coordinate analysis of the planar vibrations in the Cu‐chelates of porphin, porphin‐d4 (meso), 1:3:5:7‐tetramethyl porphin and 1:2:3:4:5:6:7:8‐octamethyl porphin

Normal coordinate calculations have been carried out for all the planar vibrations of Cuporphin, Cu‐porphin‐d4 (meso), Cu‐1:2:3:4:5:6:7:8‐octamethyl porphin and Cu‐1:3:5:7‐tetramethyl porphin. A method is presented to obtain the skeleton deformation and the CC stretching force constants in large organic molecules with delocalized double bonds from the bond length values. This method enabled a satisfactory calculation of 160 observed frequencies in the resonance Raman and infrared spectra of the four Cu‐porphins by using a valance force field containing only 12 independent parameters. Assignments for some of the stronger bands in the resonance Raman spectra of heme proteins and metallo‐porphins are discussed.