Kuclear magnetic resonance spectra and the infrared absorption between 700 and 760 cm-I have been observed a t temperatures near the melting points of the even-numbered fatty acids from Cl8 to Clo. The results are interpreted as indicating breakdown of crystalline character and onset of liquid-like motion a t scattered points in the solid structure several degrees below the melting point, and increasing in extent as the melting point is approached.A proton magnetic resonance study of anhydrous stearic acid (I) gave some quantitative indication of liquid-like molecular motion occurring in part of an otherwise rigid lattice a t temperatures several degrees below the melting point. I t seemed appropriate to look for this behavior, which was considered to be a premelting phenomenon (2), in other fatty acids and by other methods. Acids with an even number of carbon atoms from palmitic (C16) to capric (Clo) have been examined by nuclear magnetic resonance, and the change with temperature of the shape of the infrared absorption band a t about 720 cm-I has been studied for the even-numbered acids from stearic (C18) to lauric (Clz).This infrared band, which is characteristic of hydrocarbon chains (CHZ), with n >, 4, is frequently a doublet below the melting points of the compounds showing it, and a singlet above the melting point or for the compound in solution. I t has been assigned to the CH2 rocking mode (3, 4). A series of higher normal modes of CH2 rocking has been identified in the spectra of n-paraffins in the range 720-1050 cm-I (4). These bands are of much lower intensity than the first mode a t 720 cm-l, and their number depends on the length of the methylene chain. Stein has used the strong absorption of the first mode in a n investigation of the crystallinity of polyethylene (5), attributing the component of the doublet a t 720 cm-I equally to crystalline and amorphous parts of the polymer and the component a t 730 cm-I exclusively to crystalline parts. The splitting of the band was explained by the perturbation of the CH2 rocking vibration by the interaction of nearestneighbor methylene chains in the crystalline array. I t was shown (6) that the crystal field shifted the frequency of the out-of-phase rocking mode only slightly to higher energy and that the frequency of the in-phase mode was moved much further to higher energy. In an amorphous substance (solid, liquid, or solution) the unperturbed band occurs a t essentially the same frequency as the out-of-phase mode in the crystalline substance. Changes with temperature in the intensity of this band have also been used to study phase transitions in waxes (7). In the work reported here, the variation with temperature of the integrated intensity of the components of the doublet has been examined as a possible indication of loss of crystalline character in fatty acids below the melting point.The acids used in this investigation were all Eastman Kodak white label grade that were further purified by repeated recrystallizations from acetone following the...

Nuclear magnetic resonance spectra of anhydrous sodium stearate have been observed between 114° and 320 °C. The observed changes in line width and second moment suggest a grouping of the mesomorphic phases into a waxy group in which a lattice structure is preserved for the polar ends of the molecules and a group consisting of the neat and liquid phases in which diffusion takes place freely.

A broad-line fluorine magnetic resonance study of the solid addition cornpounds SF,.AsF, and IF, .AsF, slio\?s that each has two types of chemically distinct fluorine in the ratios of 1 :2 and 1:1, respecti\elq. The fine structure and the second moments of the spectra are consistent with the ionic form~~lations SF,+AsF,-and IF,+AsF,-. Bond lengths in the iodine compo~ind are discussed in relation to the observed second moinent at liquid-nitrogen temperature and the calculated rigid-lattice second ~iioment based on the detailed sodium-chloride-type crystal structure of Beaton. The chemical shifts of the fluorines in the three ionic species are measured relative to trifluoracetic acid and to HF. Reorientations of the ions in the solid state are discussed on the basis of the change in second moment with temperature for each compound. A very rough estimate of the anisotropy of chemical shift in I F , -A s F , is made from the slope of the second moment vs. field-squared line at liquid-nitrogen temperature.

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