Theoretical study on the molecular structures of dinitrophenols and trinitrophenols

The molecular structures of six positional dinitrophenol isomers and six positional trinitrophenol isomers were calculated by ab initio method and density functional theory. Calculated geometrical parameters were compared and found to be in good agreement with the data of X-ray diffraction. The molecular structure of each isomer was affected by the position of the substituents. Twist of the nitro group out of the phenyl ring was of significance for some isomers having nitro groups placed close together, and this twist was mainly affected by steric effect. The value of calculated energy was related to the molecular geometry, especially affected by steric effect. For dinitrophenols and trinitrophenols, 2,4-dinitrophenol and 2,4,6-trinitrophenol have the lowest energies, indicating that they are the most favored molecules. Although 2,4,6-trinitrophenol has strong inductive and resonance effects, it is a non-planar molecule. However, a planar geometry was observed as a transition state structure. An energy difference of less than 1 kcal/mol between these two different geometries implies that this transition can easily be observed. Intramolecular hydrogen bonding of some isomers was of the C-OH ON-C type and this bond distance was shorter than that previously studied for nitrotoluenes and nitroanilines, whose intramolecular hydrogen bonds were of the types of C-CH ... ON-C and C-NH ... ON-C, respectively. (C) 1999 Elsevier Science B.V. All rights reserved.