Benzoquinone, oxime

Another system with a tendency to polymorphism and in which one might expect the different crystal forms to be composed of different proton tautomers is benzoquinone oxime-nitrosophenol (8c). Here all materials studied proved to... 

Conceptually, the simplest pair to discuss is that of p-benzoquinone oxime and 4-nitrosophenol and their substituted derivatives, here all denoted by p-OCgH4=NOH/4-HOC6H4NO . In practice, this comparison is complicated by the fact that this species cannot be sublimed without decomposition and so we are prevented from analyzing the energetics of gas phase isodesmic reactions such as equations 38 and 39. 

The enthalpy of reaction 38 is ca 13 kJ mol" for the case of cyclohexanone wherein R R = —(CH2)5—. This difference is compatible with intermolecular hydrogen bonding as would be found for the benzoquinone oxime tautomer. In order to understand the energetics of reaction 39, we derived the solid phase enthalpy of formation of nitrosobenzene... 

If nitrosophenols are in equilibrium with quinone oximes, are nitrosoanilines in equilibrium with quinonimine oximes While in solution, 2-nitrosoanilines appear to show such behavior and crystallographic determination shows the benzenoid form is preferred . The enthalpy of formation of 4-nitrosodiphenylamine—or is it Af -phenyl-p-benzoquinone oxime—has been measured (213.1 3.2 kJmoD ), but as this value is for the solid we hesitate to make any thermochemical comparisons. Perhaps relatedly, the enthalpy of formation of 3,5-dimethyl-4-nitrosopyrazole has been determined but there are no data for any pyrazolones (1,2-diazacyclopentadienones as opposed to pyrazolinones) with which to make comparison with a putative oxime. 

Brom-4-nitroso-methylanilin in Ger], H3C.N C6H3(Br) N.OH or H3C.HN.CgH3(Br).NO. See 4-Nitroso-3-bromonethylaniline under Bromomethylaniline and Derivatives or 3-Bromo -l,4-benzoquinone-l-methylimine-4-oxime under Benzoquinone Oxime and Derivatives... 

Benzoquinone oximes (30) exhibit sidedness the structures exhibit anomalous 1H-NMR coupling constants (J21 can exceed by 0.6 Hz), and its additions show a syn selectivity.49 The apparent stereoelectronic effect is concluded to be primarily steric in origin. 

Benzoin, IV, 87 Benzoquinone, oxime, IV, 101 —, phytochemical reduction of, IV, 89 o-Benzoquinone, tetrabromo-, IV, 89 p-Benzoquinone, tetrahydroxy-, III, 48 Benzoxazole, 5-acetamido-2-methyl-, III, 351... 

H-l,4-Benzoxazine 6-Bromo-2,3-dimethoxycarbonyi-4-hydroxy-E9a, 145 (1,2-Benzoquinon-oxim/ Cu + ROOC — C = C — COOR)... 

H-l,4-Benzoxazine 2,3-Dimethoxy-carbonyl-4-hydroxy-6-methyl-E9a, 145 (1,2-Benzoquinon-oxim/ Cu + ROOC-C = C —COOR) Kohtensaure tert.-Butylperoxyes.ter-phthalimidoester E13/1, 255 (C-Cl -> C-O-OR) 1,2-Oxazol rro i-3,5-Dimethoxycar-bonyl-4-phenyl-4,5-dihydro- -2-oxid E14b, 927 (R-N02 + R-CHO)... 

The o- and p-nitrosophenols enjoy the possibility of resonance stabilization by jt-electron donation from the phenolic hydroxyl group to the nitroso group, and the o-isomer could also be stabilized by an intramolecular hydrogen bond. These species are also tautomeric with benzoquinone oximes. All of this could confound interpretation of enthalpy of formation values if only they were available—there are seemingly no measured enthalpy of formation values for o-nitrosophenol. The value for p-nitrosophenol will be discussed later in Section VI because of tautomeric ambiguity. The m-species lacks the stabilizing conjugate NO/OH interaction, and so the monomer-dimer equilibrium as found in other nitroso compounds becomes problematic—should the measurement of enthalpy of combustion be available. 

The o- and p-nitrosophenols are tautomeric with o- and p-benzoquinone oxime, respectively. Some of the nitrosonaphthols are tautomers of naphthoquinone oximes. A recent publication summarizes the current knowledge of tautomeric equilibria in solution, the composition of the solid phase and the results of theoretical smdies . While tautomeric composition in solution is very much dependent on compound structure and solvent polarity, various nitrosophenols, 2-nitrosonaphthol, l-nitroso-2-naphthol and 4-nitrosonaphthol exist exclusively as quinone oximes in the solid state. 

Of the nitrosophenols/benzoquinone oximes, only one compound has been thermochem-ically studied and in only one phase, solid 4-nitrosophenol/p-benzoquinone oxime. We welcome a new thermochemical investigation of this species, the 2-nitrosophenol, as well as of the m-isomer for which no oxime contamination or ambiguity is possible because of the absence of stable m-benzoquinones and related derivatives. 

Benzophenones—see also Hydroxybenzophenones chemical shifts for 338 Benzopyrans, formation of 619 Benzoquinone O-oxide 1057 Benzoquinone oximes 235 tautomerism in 251 Benzoquinones—see... 

The crystal structure of the benzylmercury derivative of 3,5-Bu2-1.4-benzoquinone oxime has been determined the tetrameric molecule has a quinonimine N-oxide structure (Hg>N bonding). 5-Chloromercurio-2 -deoxyiridine is monomeric in the solid state [Cl-Hg-C = 179.0(4) A. The complexes 2[Ph4P] [ (p3C)2CHg 5X2] (X=C1 or Br), formed from [(F3C)2CH5]s, have been characterized by " Hg NMR and by X-ray crystallography each of the halide anions, which are in axial sites about the metallacyclic unit, interact with all 5 Hg atoms. ... 

Triethylamine added dropwise with stirring and cooling at 0-5° to an ethereal soln. of 1,4-benzoquinone oxime and o-nitrobenzenesulfenyl chloride, and stirring continued for 5 min. 1,4-benzoquinone oxime o-nitrobenzenesulfenate. 

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