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Infrared spectra of 1,1,2,2-tetrachloroethane have been measured in the gaseous, liquid, and solid states and in solutions. Raman spectra of the same substance have been observed in the liquid and solid states. From the experimental results the equilibrium molecular forms of the rotational isomers have been determined. The normal vibrations of the molecule in the trans-and gauche-forms have been calculated as an 8-body problem, and the assignment of the observed infrared and Raman frequencies in all the states of aggregation has been made.

Infrared Spectra of Two Peptide Bonds, the Polypeptide Chain 186-3 more remote branching would not be expected to alter the curve appreciably from that of 2-methyl-2•dodecenoic acid. The absence of a 10.1 µ band in the spectrum of 2,5-dimethyl-2-heptadecenoic acid rules out at least one isomeric form of this structure. The available spectra do not provide any basis for a choice from among the other most likely structures.Note added in proof.-Recently a sample of synthetic 2,4-dimethyl-2-dodecenoic acid has become available from Professor Cason,6 and its infrared spectrum has been examined. In the region beyond 10 µ, absorption bands are found at the following wave lengths (values for the corresponding bands of C27-phthienoic acid-see Figs. 3 and 4are given in parentheses for comparison): 10.05 (10.06), 12.3 (12.50), 13.2 (13.26), 14.9 (14.92) µ. Considered together with previous evidence, these data indicate that the second branching methyl group of Cz7-phthienoic acid is in the y-position.

Infrared spectra of n-propyl chloride and bromide have been measured in the gaseous, liquid and solid states. The Raman measurement was also made in the liquid state. From the normal vibration calculation and by comparison with the spectra of ethylene chlorhydrin it has been concluded that in the liquid state both the trans and gauche forms are present and of these only the trans form persists in the solid state. The energy difference between the trans and the gauche forms has been determined by the absorption intensity measurement.

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