A Resonance Raman investigation of chlorophyll a and meso-chlorinated and ring V hydroxylated derivatives and pheophytins reveals localized vibrational modes in the chlorophyll series. Both chlorination and hydroxylation give rise to changes in both band intensity and frequency throughout the spectrum. Chlorination affects mainly the core sensitive bands with CaCm and CaN character. Hydroxylation leads to changes in the carbonyl and ring V associated bands. Small, but real spectral differences were found between the 10-epimers. ; PUBLISHED ; This work was generously supported by a Science Foundation Ireland Research Professorship award (SFI/04/RP1/B482). I am indebted to P. M. Callahan for many helpful discussions and Y. Sergeeva for assistance with the manuscript