Vibrational frequency analyses using density functional theory (DFT) resolves some structural features of purified oxidized single-wall carbon nanotubes (o-SWNTs). Both single bondCOOH and phenolic single bondOH (OHph) groups, predicted in several experimental studies to be present in o-SWNTs, were considered at the tips of armchair and zigzag tubes with varying diameters. Hydrogen bonding, where carbonyl oxygen acts as proton acceptor while phenolic OH donates the proton, leads to the most stable isomers, with a H-bond energy of 9–12 kcal/mol, almost double that of simpler systems. Vibrational frequencies of participating bonds are significantly red-shifted, which is not reflected in experimental spectra, and which leads to the conclusion that phenolic OH is likely not present at the tips of o-SWNTs.