Data are presented that describe the IR spectra of organic compounds obtained under matrix isolation conditions. Among the types of compounds examined are amides, lactones, lactams, esters, acids, alcohols, and phenols. Trends, as a function of structure, established in vapor-phase IR are shown to exist under MI conditions. The frequency (cm** minus **1) of the stretching absorption for hydroxyl groups and carbonyl groups associated with the types of compounds listed above under MI conditions is shown to be intermediate between the vapor-phase position (highest energy) and the solid-solution position (lowest energy).