On the Structure of “5-Nitrosotropolone”

Abstract

It has long been discussed whether "5-nitrosotropolone" 1 takes the nitroso structure 1A or the tautomeric oxime structure 1B. Analysis of NMR and UV spectra data in this study indicates that the tropoquinone-5-monoxime 1B is preferred. The UV absorption shift to longer wavelength at dilute solutions is attributable to the dissociated form 3.

Synthesis and virucidal activity of 5-substituted tropolones

“…Synthesis and chemical properties of 5-substituted tropolones 5-Nitorotropolone (1) was synthesized by the nitration of tropolone according to the method reported by Adachi [8]. All of the other 5-substited tropolones were synthesized via a nitrosation reaction [9][10]. Briefly, catalytic reduction of the resulting nitroso group gave aniline 3, which was converted to the corresponding iodide 4 using a Sandmeyer reaction [9].…”

Deprotonation Equilibrium of 5-Tropolonediazonium Salt Strongly Favors 1,2,5-Tropoquinone-5-diazide Structure in Certain Solvents

“…16 Recently we showed that 5nitrosotropolone exists in the tropoquinone-5-monoxime form, rather than the 5-nitroso form, by means of NMR and UV studies. 17 The diazo group is known to be powerful electronwithdrawing group, like the nitroso group. Therefore, we speculated that if 5-tropolonediazonium salt 1 is deprotonated, it may exist in the diazo form 2 (Scheme 1), which might be available as a carbene precursor, as in the case of 4.…”

“…On the other hand, diazotization of arylamines having a para hydroxy group is well-known; an example is the formation of 4-hydroxybenzenediazonium salt 3 , which has properties quite different from those of a typical diazonium salt. , Deprotonation of 3 affords 1,4-benzoquinonediazide (4-diazo-2,5-cyclohexan-1-one) 4 , which can be regarded as a cyclic vinylogue of α-diazo ketones and is used as a carbene reaction precursor (see Table for structures) . Recently we showed that 5-nitrosotropolone exists in the tropoquinone-5-monoxime form, rather than the 5-nitroso form, by means of NMR and UV studies . The diazo group is known to be powerful electron-withdrawing group, like the nitroso group.…”

NMR Spectroscopic Study of Tautomerism in Solution and in the Solid State

“…5-Nitrosotropolone in methanol solution, however, prefers the tropoquinone 5-monoxime tautomeric structure 54a (Scheme 5.41)[98]. -(α-Aminoalkyl)tetrazoles exist in solution as equilibrium mixtures of N-1 (55a) and N-2 (55b) tautomers (Scheme 5.42)[99].…”