3-Hydroxy-6-[(4-hydroxyphenylamino)methylene]cyclohexa-2,4-dienone and 2-hydroxy-6-[(4-hydroxyphenylamino)methylene]cyclohexa-2,4-dienone

Abstract

The title compounds, both C(13)H(11)NO(3), exist as the keto-amine tautomers, and the formal hydroxyl H atoms, which display strong intramolecular hydrogen bonds, are located on the N atoms. This is a verification of the preference for the keto-amine tautomeric form in the solid state. The 2-hydroxy isomer has two independent molecules, with the molecules linked by intramolecular N-H.O and O-H.O and intermolecular O-H.O hydrogen bonds into three-dimensional networks.

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.…”

Crystal Structure of N-n-Propylalcohol-2-oxo-5-nitro-1-benzylidene-methylamine

“…4 The N2-O2 and N2-O3 bond lengths are as expected for a nitro group (Table 3). Similar to this compound, a very related structure was reported in the literature.…”