Molecular structure and intramolecular hydrogen bonding in 4,6-dinitroresorcinol and 2,5-dinitrohydroquinone from ab initio molecular orbital calculations

Ab initio molecular orbital calculations using second-order Moller-Plesset (MP2) perturbation theory with the 6-31G(*) basis set have been performed for 4,6-dinitroresorcinol and 2,5-dinitrohydroquinone. Both molecules are characterized by considerable hydrogen bonding between the nitro and hydroxy groups; pronounced structural changes in other parts of the molecules are observed when compared with the parent phenol and nitrobenzene molecules calculated at the same computational level. These structural changes are consistent with the notion of resonance-assisted hydrogen bonding, also observed in a series of other 0-nitrophenols and similar molecules. The geometrical and energetic characteristics of the structures indicate somewhat weaker hydrogen bonding in 2,5-dinitrohydroquinone than in 4,6-dinitroresorcinol, which may be interpreted by the difference in the mutual orientation of the substituent pairs in the two compounds. (C) 1997 Elsevier Science B.V.