Twist-chair conformation of the tetraoxepane ring remains unchanged in tetraoxaspirododecane diamines.

A detailed structural analysis has been performed for N,N'-bis(4-chlorophenyl)-7,8,11,12-tetraoxaspiro[5.6]dodecane-9,10-diamine, C20H22Cl2N2O4, (I), N,N'-bis(2-fluorophenyl)-7,8,11,12-tetraoxaspiro[5.6]dodecane-9,10-diamine, C20H22F2N2O4, (II), and N,N'-bis(4-fluorophenyl)-7,8,11,12-tetraoxaspiro[5.6]dodecane-9,10-diamine, C20H22F2N2O4, (III). The seven-membered ring with two peroxide groups adopts a twist-chair conformation in all three compounds. The lengths of the C-N and O-O bonds are slightly shorter than the average statistical values found in the literature for azepanes and 1,2,4,5-tetraoxepanes. The geometry analysis of compounds (I)-(III), the topological analysis of the electron density at the (3, -1) bond critical points within Bader's quantum theory of `Atoms in molecules' (QTAIM) and NBO (natural bond orbital) analysis at the B3LYP/6-31G(d,2p) level of theory showed that there are nO→σ*(C-O), nN→σ*(C-O) and nO→σ*(C-N) stereoelectronic effects. The molecules of compounds (I) and (III) are packed in the crystals as zigzag chains due to strong N-H...O and C-H...O hydrogen-bond interactions, whereas the molecules of compound (II) form chains in the crystals bound by N-H...O, C-H...π and C-H...O contacts. All these data show that halogen atoms and their positions have a minimal effect on the geometric parameters, stereoelectronic effects and crystal packing of compounds (I)-(III), so that the twist-chair conformation of the tetraoxepane ring remains unchanged.