Resonance Raman spectra of porphyrins are Computed with DFT/ClS methodology to monitor out-of-plane distortions. A framework is established for assessing protein-induced distortion of porphyrin bound to a ferrochealatase antibody. Tests oil undistorted porphyrins give good agreement with the experimental intensity, pattern of in-plane modes for free-base porphine (FBP) and mesorporphyrin IX free base (MP). The computed spectrum of N-methylmesoporphyrin (NMP), in which the methyl-subsituted pyrrole fine is tilted 32degrees front the mean porpyrin plane. also gives reasonable agreement with experiment and reveals activation of out-of-plane (oop) vibrational modes. To model oop distortions systematically, an artificial molecule, FBP-X-S, was constructed, in which the H atoms attached to the FBP pyrrole C-b, atoms are replaced by heavy Substituents. as in physiological porphyrins. Oop mode enhancements are computed for FBP-X-S, by displacing it along the canonical distortion coordinates: doming. saddling, ruffling and waving. When FBP-X-s is constrained to the NMP porphyrin geometry, normal coordinate decomposition reveals significant contributions also front modes higher in frequency than the canonical modes. and the), contribute importantly to the computed RR intensities. NMP-constrained FBP-X-S gives a reasonable facsimile of the NMP RR spectrum, but better results are obtained with a full computation of MP, constrained in the same way; thus the physiological substituents have significant influence oil the RR spectra. over and above their effective masses. Attention focuses on a mode analogous to gamma(15) in 4-fold symmetric porphyrins, which is a kind of saddling mode. This mode is selectively enhanced in NMP-constrained MP; a corresponding RR band is induced upon binding MP to a ferrochelatase antibody.