We used the scaled quantum mechanical oligomer force field (SQMOFF) method to model helical and planar poly(p-phenylene) (PPP) and compared the calculated vibrational spectra with experimental data. The 3-21G basis set was found to accurately reproduce vibrational frequencies of benzene and biphenyl with a variant of Pulay’s scaling method. This scaling procedure used only 10 scaling factors. The optimized values of the scaling factors were in the 0.6912-0.8725 range as determined from benzene and biphenyl and were taken as fixed parameters in the polymer calculation. The results were a significant improvement over previously calculated frequencies, indicative of excellent transferability of scaling factors from benzene and biphenyl to the polymer. No significant difference was found between the IR spectra of helical and planar PPP. However, a better overall agreement for the Raman spectra was found with nearly planar PPP. Further evidence supporting the nearly planar model comes from the Raman intensity ratio of the 1280 to 1220 cm(-1) peaks (I-1280/I-1220) in PPP. Therefore, we concluded that the most probable structure of PPP is nearly planar. All earlier assignments of normal modes by Furukawa based on calculations by Zannonni and Zerbi, Bozovic and Rakovic, and Krichene et al. were confirmed except for two bands. Limitations of Zerbi’s R mode model were discussed with respect to Raman intensity predictions.