THE STRUCTURE OF 1,6-DIAZACYCLODODECANE-7,12-DIONE, A CYCLIC MONOMERIC MODEL OF POLYAMIDE 46

1,6-Diazacyclododecane-7,12-dione (C10H18N2O2), M(r)=198.27, monoclini c, one molecule in the asymmetric unit, P2(I)/c; a=9.802(4), b=12.966( 6), c=9.20(1) Angstrom, V=1O83(I) Angstrom(3), Z=4, D-x=1.215(2) Mg.m( -3), lambda(Cu K alpha)=1.54184 Angstrom, mu=6.5 cm(-1), F(000)=432, R =0.062 for all 866 unique observed reflection data. The molecules form hydrogen bonded stacks with two hydrogen bonds between each pair of s ucceeding molecules. The stacks consist of molecules with two alternat ing orientations, as in A-B-A-B. No strong intermolecular contacts exi st between adjacent stacks, this results in a partial two-fold positio nal disorder of the stacks in the direction of the a-axis: two adjacen t stacks can slide over half a unit cell. along the a-axis without sev erely affecting the packing. This disorder results in very broad refle ctions h not equal 2n, which could only be discerned on a rotation pho tograph. The 12-membered ring which forms the basis of the structure h as a pseudo two-fold axis through the bonds C(8)-C(10) and C(9)-C(11).