Crystal Packing of Odd-Chain Saturated Triglycerides

Single crystal electron diffraction d a ta from an odd-chain trig lyceride, glycerol trihep tadecanoate, are compared w ith the known structure o f the even-chain hom o-acid triglycerides. Both class­ es o f triglycerides are found to resem ble one ano ther in chain packing: they both have the sam e chain tilt (61 °) for the /?-polymorph and, further, the o rien ta tio n o f the T|| subcell in the crystal structure is identical. T he existence o f the Ty subcell is quan tita tively verified for the first tim e with the diffraction intensities from suitably tilted crystals. G iven these sim ilarities in /?-poly-. m orph structure, the m ajor difference betw een triglycerides w ith even or odd chains (indicated by published long spacing and melting po in t a lternation) m ust be d ue to the m ethyl end group pack­ ing — i.e., the end group packing volum e for the odd-chain glycerides m ust be larger than found for the even-chain m aterials.