The X-ray crystal structure of N-(1-hexadecyl)-d-gluconamide and powder diffraction studies on its lower and higher homologues (n = 9−18)

The crystal structure of N-(1-hexadecyl)-d-gluconamide [a = 4.8072(6) Å, b = 46.771(5) Å, c = 5.2885(7) Å, β = 94.37(1)°; monoclinic P21, Z = 2] displays the same molecular conformation and the same monolayer packing-arrangement as its lower homologues described previously. This is at seeming variance with most recent CPMAS 13C NMR solid-state investigations describing a bilayer packing. It can be shown that the bilayer arrangement is the result of a kinetically driven crystallisation process, whereas the monolayer packing is the thermodynamically stable polymorph of the title compound. Powder spectra of dried self-assembled layers of N-(1-alkyl)-d-gluconamides showed only one-dimensional order and exhibited at most two periodicities. These could be assigned to a mono- and bilayer arrangement, respectively. Derivatives with long alkyl chains proved to have a smaller tendency towards monolayer assembling than homologues with a short tail.