The infrared absorption spectra of some 700 aliphatic and aromatic hydrocarbons have been investigated from 15 to 35 mu and the characteristic absorption frequencies incorporated into spectra-structure correlation charts. The classes of compounds studied were alkanes, alkenes, cyclopropanes, cyclopentanes, clohexanes, substituted benzenes, naphthalenes and biphenyls. The skeletal bending frequencies of the alkanes and alkenes and the non-planar bending frequencies of the aromatic hydrocarbons are the most useful for qualitative analysis in this region. The wavelength and intensity of the out-of-plane ring frequencies of aromatic molecules give some indication of the nature of the substituents. Typical infrared spectra of the hydrocarbons are presented.