NMR and X-ray studies of 2,6-bis(alkylimino)phenol Schiff bases

Schiff Bases from TRIS and ortho‐Hydroxyarenecarbaldehydes: Structures and Tautomeric Equilibria in the Solid State and in Solution

“…[41] A similar trend can be inferred from 15 N NMR spectroscopy, since the imine nitrogen atom is much more shielded than that atom in the enamine tautomer (δ ≈ -63 ppm vs. δ ≈ -247 ppm). [42,[44][45][46][47][48] In the present case, the carbon resonance at δ ≈ 165 ppm for compounds 20 and 21 can be attributed to C-2 in a phenol-imine structure, whereas 22 shows a signal at δ ≈ 180 ppm, consistent with a keto-enamine structure. Moreover, 13 C NMR spectra for 20 and 21 are essentially identical, with the sole exception of the C-5 signal at δ ≈ 107 ppm for the former and at δ ≈ 77 ppm for the latter, owing to the distinctive presence of halogen atoms (Br and I, respectively) linked to that carbon atom.…”

Synthesis, crystal structures and antibacterial activity studies of aza-derivatives of phytoalexin from cotton plant – gossypol

“…In the spectrum of GOS the signal of C(7) carbon atom was found at 155.6 ppm in CDCl 3 [54] and at 151.4 ppm in CD 3 CN [55], whereas the signal of C(7) carbon atom in the spectra of 19-27 was in the range 150.1-157.3 ppm ( Table 5). The chemical shift of the C(7) signals of gossypol hydrazones (19)(20)(21)(22)(23)(24)(25)(26)(27), similar to those of GOS, are in the range characteristic of the C-OH carbon atoms of phenols [46,[56][57][58][59]. This result shows clearly that gossypol hydrazones are present in the N-imine-N-imine tautomeric form, which is analogous to the aldehyde-aldehyde form of GOS (Scheme 1).…”

2,2′-[(Propane-1,3-diyldinitrilo)bis(phenylmethylidyne)]diphenol

“…There are two strong intramolecular O-H..O hydrogen bonds involving the hydroxyl and imine groups forming S(6) ring motifs (Bernstein et al, 1995). These types of hydrogen bonds are common to some reported molecular structures (Schilf et al, 2007;Fernández et al, 2001;Kabak, 2003;Wojciechowski et al, 2001;Dey et al, 2001;Koşar, et al, 2004;Lu, et al, 2008;Qiu & Zhao, 2008;Montazerozohori et al, 2009;Corden et al, 1996). In the crystal structure, weak intermolecular C-H•••O hydrogen bond connect molecules to form a two-dimensional network.…”

“…The title compound forms part of the group of Schiff bases with a similar method of synthesis as described in Schilf et al (2007). The intermolecular hydrogen bonds O-HÁ Á ÁN between the hydroxy and imine are common to this type of compound as shown with the series of compounds reported by Ferná ndez et al (2001); Kabak (2003); Wojciechowski et al (2001); Dey et al (2001); Koşar, et al (2004); Lu, et al (2008); Qiu & Zhao (2008); Montazerozohori et al (2009); Corden et al (1996).…”