The crystal structure of cholesteryl 17-bromoheptadecanoate

Crystals of cholesteryl-17-bromoheptadecanoate (C44H77BrO2) are monoclinic (P21) with a = 7.663(2), b = 10.311(5), c = 55.96(2) A and beta = 103.10(3 degrees). These are two molecules in the asymmetric unit which have different conformations of the cholesterol side chain and about the ester bond. The molecules pack with regions of only steroid skeleta alternating with regions of hydrocarbon chains. Due to the packing requirements of the skeleta the carbon chains are forced into a hybrid type packing which contains features of the earlier known O perpendicular and T parallel subcells. The subcell (HS1) is orthorhombic with as = 10.3, bs = 7.5 and cs = 2.54 A. The molecular packing is such that the omega-bromine atoms do not continue the trans-carbon chains but adopt a gauche conformation.