elation of strong bands found in related series suggests assignments of some of the frequencies t o vibrations of particular parts of the nuclear frameworks, which may be useful in disentangling the spectra of complex molecules containing these groupings. The results are also useful in suggesting key bands for infra-red analysis of mixtures of these compounds, or for the detection of impurities.THE use of infra-red spectra for both analysis and structural diagnosis demands the measurement of the spectra of many compounds differing in type over a wide spectral range. By this means, characteristic differences may be found giving key absorption bands for analysis, but a t the same time the comparison of spectra of related compounds may lead to an assignment of vibration frequencies which are characteristic of particular types of nuclear skeleton. Such data can only be applied successfully in the study of complex or macromolecules if measurements are first made, for purposes of reference, on relatively simple molecules, where the assignment of frequencies can be made with conviction. Compilations of this kind have been published recently, and some important correlations obtained (Barnes, Liddel, and Williams, Ind. Eng. Chenz. A naE., 1943, 15, 8 3 ; Thompson and Torkington, Proc. Roy. SOC., 1945, A , 184,3; '1'rans. Faraday SOG., 1945,41, 246).In connexion with the elucidation of the vibrational spectra of some polymers containing ester groupings, we have measured the spectra of many esters and ketones between 2 p and 20 p. Some of the results are collected here, and the spectra are discussed briefly from the standpoint of molecular structure. A complete correlation of the infra-red absorption frequencies with the corresponding Kaman intervals would a t present become unwieldy, and will therefore be deferred until the most important features can be disentangled from the much larger number of molecules under examination.A few were prepared in this laboratory. I n many cases two or more samples of the same compound were examined, the identity of the spectra serving as a check on purity. Benzophenone was measured as a solid film on rocksalt; the remainder were measured as liquids in an absorption cell made by separating plates of rock-salt by a washer about 0.08 mm. thick. The spectrometers have already been described (Thompson and Whiffen, this vol., p. 268).The spectra are shown as charts, Figs. 1-7, in which bands are shown as lines of varying intensity covering the spectral range 500-1750 wave numbers. The disadvantage of this form of representation is that it does not reveal the relative breadths of the bands, and the intensities can only be regarded as approximate, but itThe vibrational spectra *of a number of ketones and esters have been measured between 5-20 p.The compounds employed were usually commercial products, purified by fractionation.