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

Abstract

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 n O→σ*(C—O), n N→σ*(C—O) and n O→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.