252 111. CHEMISTRY OF NEUTRAL FATS 



that all three polymorphic forms of tristearin are crystalline, and that the 



7- or glassy form does not exist. These polymorphic modifications are 



designated as follows by Lutton : a (lowest melting and identical with the 



a-form of Clarkson and Malkin^^'^) ; jS' (intermediate melting point and not 



observed by Clarkson and Malkin'*^ in the case of simple triglycerides, but 



reported by them for mixed triglycerides); j8 (highest melting and stable 



form, identical with the product similarly designated by Clarkson and 

 Malkin3«2) 



a. Simple Triglycerides. The data on the melting points and the x-ray 

 spacings of the polymorphic forms of the simple glycerides composed of 

 the common saturated and unsaturated fatty acids are summarized in 

 Table 27. 



The melting point data on the a- and /3-forms of tristearin of Clarkson 

 and Malkin,^^- Lutton, ^^^ and Filer and co-workers ^^"^ are in excellent agree- 

 ment. The same is true for the data of Clarkson and Malkin**- and of 

 Filer et aL™ on trielaidin. 



Alternation of melting points is observed only with the stable modifica- 

 tion (/3-form), while the values for the melting points of the less stable forms 

 are straight-line functions (Fig. 7). On the other hand, the long x-ray 

 spacings do not exhibit alternation with any of the crystalline modifica- 

 tions (Fig. 8). 



The structure of the three polymorphic forms of simple triglycerides of 

 the saturated acids apparently agrees with the "tuning fork" arrangement 

 suggested by Malkin et al.,^^'^ which is illustrated in Figure 9. 



This conception is likewise in harmony with the data of Lutton^^^ ob- 

 tained by x-ray diffraction studies. Such structures are termed DCL 

 (double chain length) , in contrast to TCL (triple chain length) which occurs 

 with some mixed triglycerides, and QCL (quadruple chain length), which 

 has also been noted. 



Ferguson and Lutton^^^ have confirmed the earlier finding of Wheeler 

 et al.^*^ that triolein may exist in three polymorphic forms each with 

 distinct melting points. The long spacings for triolein is somewhat less 

 than for tristearin; the shortening is especially evident in the case of the a- 

 modification, which is unusual. For this reason, Ferguson and Lutton"^ 

 suggest that it must involve a tilted form. 



The short spacings for the triglycerides made up of even-chain saturated 

 acids are identical at 3.7, 3.9, 4.6, and 5.3 A., while the pattern varies 

 slightly for those composed of odd-chain acids, in which case the spacings 



3«9 E. S. Lutton, J. Am. Chem. Soc, 68, 676-679 (1946). 



™ L. J. Filer, Jr., S. S. Sidhu, B. F. Daubert, and H. E. Longenecker, /. Am. Chem. 

 Soc, 68, 167-171 (1946). 



3^1 E. S. Lutton, /. Am. Chem. Soc, 70, 248-254 (1948). 



372 R. H. Ferguson and E. S. Lutton, J. Am. Chem. Soc, 69, 1445-1448 (1947). 



