The polymorphism of odd and even saturated single acid triglycerides, C8–C22

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Abstract
The polymorphism of single fatty acid odd triglycerides, C11 through C17 has been reinvestigated, with extension of the study to C9, C19 and C21. With study of the even glycerides C8, C20 and C22 it has been possible to review the whole series (odd and even) C8 through C22. The odd glycerides resemble the even in showing three distinct melting levels. Lowest melting forms are α. Stable forms are β except for C9 and C11 which show a different structure type. Intermediate melting β′ forms of odd glycerides are substantially more stable than their even counterparts as well illustrated by differential thermal analysis. There are no vitreous forms. Alternation in mp (between odd and even) is confirmed for stable phases and nonalternation for α and (within experimental error) for β′. Both β′ and β long spacings show alternation but not α. Alternation is evident in the short spacings of β′ and β forms. While short spacings of β′ forms of even triglycerides are much alike especially for C14 through C22, those of odd glycerides show a fortuitous 4‐carbon cycle. This appears to involve no significant structural variation as chain length increases but simply an approximate 4‐carbon cycle of variation in diffraction details derived from the presumed unvarying 0 ⊥ type subcell structure.