Intramolecular Hydrogen Bonding and Molecular Geometry of 4,6-Dinitroresorcinol from Gas-Phase Electron Diffraction

Article abstract of DOI:10.1021/j100038a010

The molecular geometry of 4,6-dinitroresorcinol has been determined by gas-phase electron diffraction.The resonance-assisted intramolecular hydrogen bonding is accompanied by pronounced bond length changes as compared with the parent molecules phenol and nitrobenzene.The molecular geometry is characterized by the following bond lengths (r_g) and bond angles: (C-H)_mean, 1.086 +/- 0.015 Angstroem; (C-C)_mean, 1.402 +/- 0.003 Angstroem; C₃-C₄, 1.424 +/- 0.005 Angstroem; C-O, 1.341 +/- 0.004 Angstroem; O-H, 1.002 +/- 0.009 Angstroem; C-N, 1.461 +/- 0.004 Angstroem; (N-O)_mean, 1.233 Angstroem; <*>C₁-C₂-C₃, 120.3 +/- 0.4 deg; <*>C₂-C₃-C₄, 119.3 +/- 0.3 deg; <*>C₃-C₄-C₅, 121.6 +/- 0.3 deg; <*>C₄-C₅-C₆, 118.0 +/- 0.4 deg; <*>C₄-C₃-O, 123.4 +/- 0.3 deg; <*>C-O-H, 104.5 +/- 1.4 deg; <*>C₃-C₄-N, 121.0 +/- 0.2 deg; (<*>C-N-O)_mean, 118.1 +/- 0.1 deg; <*>O-N-O, 123.7 +/- 0.2 deg.The effective angle of nitro group torsion from electron diffraction is 14.4 +/- 1.3 deg.If it is assumed that this effective angle of torsion emerges as a consequence of torsional vibrations about the planar equilibrium conformation, then a barrier to internal rotation of 18 +/- 3 kJ/mol may be estimated, the same as in nitrobenzene, the planarity of which is consistent with microwave spectroscopic results.