Comparative analysis of crystal structures of E,E-configured para-substituted acetophenone azines with halogen, oxygen, nitrogen and carbon functional groups

Abstract

A comparative analysis is presented of the solid state structures of fifteen E,E-configured para-substituted acetophenone azines with halogen [–F (1a), –Cl (1b), –Br (1c)], oxygen [–OMe (2, 5 and 6), –OH (3), –OCOEt (3)], nitrogen [–NMe₂(7), –NH₂(8), –NHCOMe (9), –NO₂(10)] and carbon [–Me (11), –CO₂Et (12), –CN (13)] functional groups. The X-ray crystal structures of 2, 7–10 and 12 were determined and are reported. The data allow us systematically to examine the structural effects of the nature of the para-substituent in a series of closely related azines and to assess and distinguish between intrinsic electronic and steric effects and consequences of crystal packing. Stereoelectronic effects of the para-substituents are discussed in terms of contributions of various resonance forms and structural parameters are identified that may serve as indicators of their importance. Analyses are presented of conformational properties and of crucial bond lengths of the azines 1–13. The molecules also are analysed as para-disubstituted benzenes X–C₆H₄-Az and compared with X–C₆H₄-Z systems qualitatively to rank the electron-withdrawing ability of the Az group.