INTRAMOLECULAR HYDROGEN-BONDING AND MOLECULAR-STRUCTURE OF 2-NITRORESORCINOL FROM GAS-PHASE ELECTRON-DIFFRACTION

The molecular structure of 2-nitroresorcinol has been determined by electron diffraction in the gas phase. The formation of strong intramolecular hydrogen bonding between the nitro group oxygen and hydroxy hydrogen is indicated by the short H...O nonbonded distance, 1.76 +/- 0.04 angstrom. The 0 ... 0 nonbonded distance (between the nitro and hydroxy groups), 2.56 +/- 0.01 angstrom, is also much shorter than twice the oxygen van der Waals radius. The hydrogen bond makes a 110.5 +/- 1.5-degrees angle with the N=O bond corresponding to the direction where one of the oxygen lone pairs of electrons is anticipated. There are considerable bond length changes, as compared with nitrobenzene and phenol, consistent with strong resonance-assisted hydrogen bonding. In addition to the through-bond interactions connected with the H ... 0 bond formation, angular changes suggest a through-space repulsive intersubstituent effect. The benzene ring geometry indicates a marked departure from additivity of individual substituent effects. The molecular geometry of 2-nitroresorcinol is characterized by the following bond lengths (r(g)) and bond angles: N=O, 1.239 +/- 0.003 angstrom; N-C, 1.449 +/- 0.007 angstrom; (C-C)mean, 1.404 +/-0.003 angstrom; C1(N)-C2,1.426 +/- 0.005 angstrom; C2-C3/C3-C4, 1.393 +/- 0.004 angstrom; (C-H)mean, 1.090 +/- 0.015 angstrom; C-O 1.354 +/- 0.004 angstrom; 0-H, 1.038 +/- 0.015 angstrom; 0-N=0, 121.4 +/- 0.5-degrees; O=N-C, 119.3 +/- 0.3-degrees; N-C-C, 120.5 +/- 0.4-degrees, C1(N)-C2-0, 122.8 +/- 0.7-degrees, C-0-H, 116 +/- 3-degrees, C6-C1-C2, 119.1 +/- 0.7-degrees, C1-C2-C3, 120.4 +/- 0.5-degrees; C2-C3-C4, 118.3 +/- 0.50, C3-C4-C5, 123.6 +/- 0.6-degrees.