Abstract
To study the influence of intra- and intermolecular interactions on properties of the nitro group in para-substituted nitrobenzene derivatives, two sources of data were used: (i) Cambridge Structural Database and (ii) quantum chemistry modeling. In the latter case, “pure” intramolecular interactions were simulated by gradual rotation of the nitro group in para-nitroaniline, whereas H-bond formation at the amino group allowed the intermolecular interactions to be accounted for. BLYP functional with dispersion correction and TZ2P basis set (ADF program) were used to perform all calculations. It was found that properties of the nitro group dramatically depend on both its orientation with respect to the benzene ring as well as on the substituent in the para-position. The nitro group lies in the plane of the benzene ring for only a small number of molecules, whereas the mean value of the twist angle is 7.3 deg, mostly due to intermolecular interactions in the crystals. This distortion from planarity and the nature of para-substituent influence the aromaticity of the ring (described by HOMA index) and properties of the nitro group due to electronic effects. The results obtained by QM calculations fully coincide with observations found for the data set of crystal structures.
Highlights
The nitro group is one of the most frequently encountered substituents in organic chemistry [1].In the Cambridge Structural Database (CSD) [2], 38406 crystal structures of chemical compounds containing the NO2 group are reported, whereas considering more precise measurements—the numbers are 36030 and 20662 with R-factor equal to or less than 0.10 and 0.05, respectively
Three sources of molecular geometry deformations in para-substituted nitrobenzene are discussed: (i) substituents; (ii) intermolecular interactions when the molecule is subjected to derivatives are discussed: (i) substituents; (ii) intermolecular interactions when the molecule is chemical reactions, e.g., by protonation process; and (iii) interactions in crystals
For both oxygen atoms of theinteractions, nitro group oxygen nitroangle groupofparticipating in a similar number of intermolecular participating in a similar of intermolecular dihedral is close to the one the dihedral angle is closenumber to the one found for the interactions, mean value; the in the case ofangle para-dinitrobenzene it found forto theca.mean value; in the case of para-dinitrobenzene it amounts to ca. 10the degtwo
Summary
The nitro group is one of the most frequently encountered substituents in organic chemistry [1]. In the Cambridge Structural Database (CSD) [2], 38406 crystal structures of chemical compounds containing the NO2 group are reported, whereas considering more precise measurements—the numbers are 36030 and 20662 with R-factor equal to or less than 0.10 and 0.05, respectively This particular interest in nitro-compounds is due to their very important properties. Understanding of structural aspects of this group is very important because nitro-compounds reduces by almost a half, from 1.27 for planar conformation to 0.72 for the perpendicular one [7]. (i) of para-substituted nitrobenzene derivatives systems a substantial variability ofdeformations aforementioned properties [12] To this have these systems a substantial variability of aforementioned properties [12].end, To we this end,undertaken wefound have in the solid state; controlled deformations out by rotation of thederivatives nitro ingroup in detailed studies on: (ii).
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