2-[(2-Hydroxy-4-nitrophenyl)aminomethylene]cyclohexa-3,5-dien-1(2H)-one

Abstract

The title compound, C(13)H(10)N(2)O(4), adopts the keto-amine tautomeric form and displays an intramolecular N-H...O [N...O = 2.579 (2) A] and three intermolecular O-H...O [O...O = 2.561 (2) A] and C-H...O [C...O = 3.274 (2) and 3.318 (2) A] hydrogen bonds. The keto-amine structure is favoured by through-molecule conjugation between the hydroxy O atom and imine N atom. The dihedral angle between the planes of the two aromatic rings is 10.79 (4) degrees.

Structural and aromatic aspects for tautomerism of (Z)-6-((4-bromophenylamino)methylene)-2,3-dihydroxycyclohexa-2,4-dienone

“…The former is of single bond character in OH (phenol-imine) tautomers and of double bond character in canonical NH (keto-amine or quinoid) tautomers, while the latter is of double bond in OH (phenol-imine or benzenoid) tautomers and of single bond in canonical NH (keto-amine) tautomers as shown in Chart 1b. While C13-O1 bond length (Table 2) is in well agreement with those of similar NH (cis-keto amine) tautomers in the literature [29][30][31][32][33], C7-N1 and C7-C8 bond lengths are somewhat longer than their corresponding values in [29][30][31][32][33], indicating more single bond character of them. Although C ar =C(sp 2 ) bond distances in these compounds varies from 1.391 to 1.404 Å [29][30][31][32][33], it is found as 1.412(9) Å in this study.…”

“…While C13-O1 bond length (Table 2) is in well agreement with those of similar NH (cis-keto amine) tautomers in the literature [29][30][31][32][33], C7-N1 and C7-C8 bond lengths are somewhat longer than their corresponding values in [29][30][31][32][33], indicating more single bond character of them. Although C ar =C(sp 2 ) bond distances in these compounds varies from 1.391 to 1.404 Å [29][30][31][32][33], it is found as 1.412(9) Å in this study. As a result of partial quinoid effect in the compound, C7-C8 bond length is essentially intermediate between single and double C ar to C(sp 2 ) bonds those in NH [29][30][31][32][33] and OH [34] tautomers.…”

“…Although C ar =C(sp 2 ) bond distances in these compounds varies from 1.391 to 1.404 Å [29][30][31][32][33], it is found as 1.412(9) Å in this study. As a result of partial quinoid effect in the compound, C7-C8 bond length is essentially intermediate between single and double C ar to C(sp 2 ) bonds those in NH [29][30][31][32][33] and OH [34] tautomers. Depending on proton transfer, not only do the most indicative bonds vary, but also certain C ar -C ar bond lengths (Chart 1b) deviate from their optimal values (1.388 Å ) and thus, aromaticity …”

“…Valences of tautomeric proton located in the center of the hydrogen bridge are obtained as 0.829 and 0.905 with regard to geometric details of H-bonds in [37,40], while those of other stable tautomeric forms in [37,40] are higher than 1.00 in the interval of 1.015-1.214. Total valence of the tautomeric proton in the crystallographically observed geometry of the compound is found as 1.376 and this value is in the interval of 1.070-1.487 calculated for the similar compounds [29][30][31][32][33]. It is inferred from these computational results that excess valence of the tautomeric proton in the initial OH form leads to proton transfer reaction and the tautomerization results in almost formal single valence of the tautomeric proton for both stable OH and NH form in gas phase.…”

Synthesis and photophysical characterization of a Schiff base as anion sensor

“…The acidity of the amine or the conjugated phenol is relatively high as indicated by the appearance of a peak at 13.24 ppm and it has been reported [44] that salicylidenes exist in the phenol-imine tautomer in DMSO solution while in other solvents the keto form predominates. There have been many examples [45][46][47][48] of X-ray data showing analogous compounds in the keto-amine form in the solid state and studies on the keto-amine phenol-imine tautomerism [49][50][51].…”