The polymorphism of 13 single acid triglycerides with acyl group chain lengths ranging from 16–22 was studied by differential scanning calorimetry. In contrast to the singleβ′‐form generally attributed to such triglycerides, at least two intermediate endotherms were found for most samples between the least stable (α) and most stable (β) polymorphs. For saturated triglycerides, two versions of the familiar “tuning fork” model meet theβ′‐form requirement of alternate fatty acid chains in planes perpendicular to each other. The detection of three intermediate endotherms for triolein, tri‐cis‐1 1‐octadecenoin and trierucin (and possibly also trilinolein) may be rationalized by assuming that the segments of polymethylene chains on either side of double bonds may zigzag in different planes. Four exceptions for which no evidence was found forβ′‐forms are tri‐cis‐6‐octadecenoin, tri‐cis‐6‐hexadecenoin, tri‐trans‐6‐octadecenoin and trielaidin. Three of these exceptions contain Δ6‐acyl groups and have in common segments with even numbers of methylene groups on either side of the double bonds. These same three triglycerides also have a shorter than usual polymethylene segment between the ester linkages and the double bonds and a longer than usual distance from the double bonds to the terminal methyl groups. Tri‐trans‐6‐octadecenoin and trielaidin are exceptional in still another way. Only they and are exceptional in still another way. Only they and trierucin exhibited significant nonconformity with an empirical relationship between melting points and heats of fusion ofβ‐forms. Otherwise, all points in a plot of the former physical constants vs. the latter closely fit a smooth curve, the positive slope of which gets larger as the X‐axis values, i.e., melting points, increase.

Data from Raman spectroscopy, X‐ray diffraction analysis, differential scanning calorimetry and features of the preparative method are all consistent with the existence of 2 intermediate β’ phases for tristearin; the first, a lower melting phase, β’2, transforms at 61 C into the second, β’1 , which in turn changes at 64 C into β‐tristearin. Raman spectral evidence indicates that the 2 mesophases occur in an orthorhombic packing environment and that the β’2 to β’1 transition results from a change in lateral packing of the hydrocarbon chains.

Differential scanning calorimetry studies on saturated monoacid triglycerides were extended to include most odd and even chain lengths from tricaprylin (Cs) through tritriacontanoin (C30). Two /~'-forms were common with triglycerides C1s through C2,: shorter odd chain length triglycerides (C9-C13) exhibited only one 3'-form; short even chain length triglycerides (Ca-C14) exhibited three. Odd Chain length C2t and C23 triglycerides showed two B-forms. Trigly-1Presented in part at AOCS Meeting, Philadelphia, PAfrom rapid cooling exotherm for Cs-Cts. bCooling rate = 0.625 C/rain. CData from ref. 7. dData in part from ref. 7.

Six theoretical triarachidin space‐filling α‐form structures were examined using a computer modeling technique that simulated restricted oscillations of carbon zigzag planes in synchronous and nonsynchronous modes. Intermolecular minimization procedures determined best‐fit positions around a centralized molecule, which enabled calculation of total lattice energy values for nine different hexagonal subcell arrangements. Subcell arrangement had a greater effect on the energy of the system than did the configuration of the triglyceride. The analysis thus far indicates several equally preferred structure‐sub cell arrangement combinations for triglyceride α‐forms rather than a single crystalline entity.