Oxygen Atoms Of Nitro Group Research Articles

ChemInform Abstract: GAS PHASE ELECTRON DIFFRACTION STUDY OF THE MOLECULAR STRUCTURE OF 6,6′‐DINITRO‐2,2′‐DIPHENIC ACID

Abstract The 6,6′-dinitro-2,2′-diphenic acid molecule has been studied by gas phase electron diffraction. The structure analysis (based on C i symmetry for the molecule as a whole and D 6h , C 2v and C s symmetries for the phenyl rings, the nitro and carboxyl groups, respectively) gives the following parameters (bond lengths, r a , in A; angles in degrees): ; CC ⪕ = 1.505 (14); CO = 1.212(8); CO = 1.409(21); CCO = 126.6(1.6); CCO = 111.8(1.3); the angle between the planes of the two phenyl rings, 71.2(0.7); the torsional angle of nitro groups, 30.4(1.4); the torsional angle of carboxyl groups, 25.1(1.5). The uncertainties given in parentheses represent three times the standard deviation values. The results are compared with the structural data on biphenyl derivatives, monomers and dimers of organic acids. The observed distances between the oxygen atoms of nitro groups and the oxygen atoms of hydroxyl groups are 2.693(26) A which may offer strong support for intramolecular hydrogen bonding.

Gas phase electron diffraction study of the molecular structure of 6,6′-dinitro-2,2′-diphenic acid

The 6,6′-dinitro-2,2′-diphenic acid molecule has been studied by gas phase electron diffraction. The structure analysis (based on C i symmetry for the molecule as a whole and D 6h, C 2v and C s symmetries for the phenyl rings, the nitro and carboxyl groups, respectively) gives the following parameters (bond lengths, r a, in Å; angles in degrees): ▪; CC ⪕ = 1.505 (14); CO = 1.212(8); CO = 1.409(21); CCO = 126.6(1.6); CCO = 111.8(1.3); the angle between the planes of the two phenyl rings, 71.2(0.7); the torsional angle of nitro groups, 30.4(1.4); the torsional angle of carboxyl groups, 25.1(1.5). The uncertainties given in parentheses represent three times the standard deviation values. The results are compared with the structural data on biphenyl derivatives, monomers and dimers of organic acids. The observed distances between the oxygen atoms of nitro groups and the oxygen atoms of hydroxyl groups are 2.693(26) Å which may offer strong support for intramolecular hydrogen bonding.

The Effects of Ion-pair Formation on the ESR Spectra of the Anion Radicals of 4-Nitropyridine N-Oxide and 4-Nitropyridine

Abstract The effect of potassium ion-pair formation on the ESR spectra of the anion radicals of 4-nitropyridine and its N-oxide (4NPO) was studied at various temperatures lower than room temperature. The hyperfine splitting constant values due to hydrogen, nitrogen, and potassium nuclei were determined by applying the simulation technique. The above value arising from the potassium nucleus, decreased with a decrease in the temperature. Molecular orbital calculations covering the whole system of the 4NPO−–M+ ion pair and employing the McLachlan modification for the spin-density calculation were carried out in order to discuss the configuration of the ion pairs and the temperature dependence of the hyperfine coupling constants. It was reasonably concluded that an alkali metal cation occupies the C2 axis of the anion radicals and is in contact with the nitro-group oxygen atoms (the symmetry of the ion pairs is C2v.). The temperature dependence of the hyperfine splitting constants was explained using the vibrational model of Atherton and Weissman.

The origin of high ortho:para-reactivity ratios in the reactions of fluoronitrobenzenes with potassium t-butoxide in t-butyl alcohol

Kinetic data for fluorine substitution of 1-fluoro-2- or 1-fluoro-4-nitrobenzene by potassium methoxide in methyl alcohol in the presence or absence of added dicyclohexyl-18-crown-6 or by potassium t-butoxide in t-butyl alcohol in the presence of the crown ether are reported. The crown ether has a negligible influence on the kinetics of the reactions of potassium methoxide where the ortho:para-activation ratio is around unity. In sharp contrast, comparison with previous data for the reactions of the same substrates with potassium t-butoxide in t-butyl alcohol shows that on addition of the crown ether (in equimolar quantities to the nucleophile, with consequent nearly total removal of potassium cation from the bulk system), the rate of reaction of the o-nitro-substituted substrate is increased by only a factor of three while that of the p-nitro-substituted substrate is increased by a factor of nearly 2000. Consequently, the ortho:para-ratio changes from 3·6 × 102 in the absence to ca. 1 in the presence of the crown ether. These results show that the high value of the ortho:para-ratio obtained in t-butyl alcohol in the absence of addenda can be attributed mainly to specific stabilization of the transition state of the reaction of the o-nitro-substituted substrate by potassium cation bridging between the nucleophile and nitro-group oxygen atoms. This intramolecular assistance is a consequence of the low polarity and low dissociating ability of the medium used, t-butyl alcohol, and does not appear when the medium is more polar and dissociating, like methyl alcohol.