284 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 100 13 t• 14.5 Wavelength Figure 1.--Absorption spectrum of petrolatum: top curve, molten, 75ø bottom curve, solid 23 ø. 13 • 15 Wavelength Figure 2.--Absorption spectrum of I G Wax Z: ----- solid, room temp, ..... molten, 120 ø . Others have studied n-paraffins such as n-nonane, n-decane, and n-tetra- decane in crystalline state (4) and observed the doublet, and Sutherland (5) correlated it with the transition point of the substance. The doublet persists until the transition point is reached but is a singlet in the liquid state. Our own observations have borne out this observation. Figure 1 shows the 13-15• region of the infrared absorption spectrum of petrolatum, which essentially consists of n-hydrocarbons. Upon melting, the doublet dis- appears but can be recovered if the sample is placed shortly on a piece of

INFRARED C--H FREQUENCIES, THEIR SIGNIFICANCE 285 dry ice in order to resolidify it. The same behavior at a higher transition temperature can be demonstrated for the case of I G wax Z, shown in Fig. 2. That the doublet disappears not only on melting but also upon dis- solving is shown in Fig. 3 for Utah wax where the solution in iso- octane shows but the single band. The most satisfying explanation of what he terms "infrared di- chroism" has just been advanced by Krimm (6) who pointed out that the two components arise from in-phase/out-of-phase rock- ing of CH.o groups on adjacent chains. The importance of infrared measurements and observation in the cosmetic industry has been pointed out repeatedly (7, 8). We have studied a number of natural and synthetic products (Table 1) particularly with reference to the doublet CH2-rockingeffect. From the above remarks we believe that this phenomenon permits a statement as to the nature, i.e., linearity of the hydrocarbon por- tion of the solid material under ob- servation and constitutes a useful qualitative analytical parameter. 13 •, 15 Wavelength Figure 3.--Absorption spectrum of Utah wax: -- iso-octane• solvent -- Utah Wax in iso-octane ---- Utah Wax, solid, room temp. .... Utah Wax, molten, 120 ø . It should be pointed out that glyceryl monostearate, and both Bayberry and Japan wax, which are mainly glycerides, do not show the doublet. A possible explanation could be that the glyceryl portion of the molecules prevents them from packing close enough for the CH2 in adjacent chains to show any in-phase/out-of-phase rocking. BIBLIOGRAPHY (1) Thompson, H. W., and Torkington, P., Proc. Roy. Soc., A184, 3 (1945). (2) Elliot, E. J., Ambrose, E. J., and Temple, R. B.,'•'. Chem. Phys., 16, 877 (1948). (3) Simanouti, T., ibid., 17, 734 (1949).