Deuterium Isotope Effects on 13C-NMR Chemical Shifts of 10-Hydroxybenzo[h]quinolines

Abstract

Deuterium isotope effects on 13C-NMR chemical shifts are investigated in a series of 10-hydroxybenzo[h]quinolines (HBQ’s) The OH proton is deuteriated. The isotope effects on 13C chemical shifts in these hydrogen bonded systems are rather unusual. The formal four-bond effects are found to be negative, indicating transmission via the hydrogen bond. In addition unusual long-range effects are seen. Structures, NMR chemical shifts and changes in nuclear shieldings upon deuteriation are calculated using DFT methods. Two-bond deuterium isotope effects on 13C chemical shifts are correlated with calculated OH stretching frequencies. Isotope effects on chemical shifts are calculated for systems with OH exchanged by OD. Hydrogen bond potentials are discussed. New and more soluble nitro derivatives are synthesized.

Dynamics of excited state proton transfer in nitro substituted 10-hydroxybenzo[h]quinolines

“…The title compounds are synthesized and purified according to the already described procedures. 13,14 They are dissolved with a concentration in the order of 10 -4 M in acetonitrile of Uvasol quality (Merck). Fused silica cuvettes with a thickness of 1 mm are employed as sample cells.…”

Isotopic splitting patterns in the 13C NMR spectra of some partially deuterated 1‐aryl‐2‐(phenyldiazenyl)butane‐1,3‐dione and 4‐hydroxy‐3‐(phenyldiazenyl)‐2H‐chromen‐2‐one: evidence for elucidation of tautomeric forms

“…One of the most distinguished works about deuterium isotope effects on 13 C chemical shifts have been reported by Hansen et al , who worked on deuterium isotope effects on chemical shifts in intramolecular hydrogen‐bonded systems, especially resonance assisted hydrogen bonding . In those cases, it has been shown that the isotope effect may be transmitted across the hydrogen bonds and may affect the chemical shifts in hydrogen‐bonded systems .…”

“…In those cases, it has been shown that the isotope effect may be transmitted across the hydrogen bonds and may affect the chemical shifts in hydrogen‐bonded systems . Also the variable‐temperature nuclear magnetic resonance (NMR) study of the enol forms of benzoylacetones and corresponding isotope effect, deuterium isotope effects on 13 C chemical shifts of nitromalonamide, 10‐Hydroxybenzo[ h ]quinolines, enaminocarbonyl derivatives of Meldrum's and Tetronic acid, o ‐hydroxy Schiff bases by applying factor analysis and tautomerism of an intramolecular O‐H...O...H‐N‐charge of the 15 N labeled Schiff base 3‐carboxy‐5‐methyl‐salicylidenaniline have been studied by means of the 1 H and 15 N NMR spectroscopy . Deuterium isotope effects in 13 C NMR spectra of intramolecularly hydrogen‐bonded salicylaldehyde‐4‐phenylthiosemicarbazone has also been studied by means of NMR spectroscopy by Novak et al …”

10-Hydroxybenzo[h]quinoline: switching between single- and double-well proton transfer through structural modifications

“…According to the NMR results in N,N-dimethylformamide (DMF) the 7,9-dinitro derivative 3 is fully in the keto form. 23 The 1 H chemical shis in DMF-d 7 (H-2, Hx) of 1 (9.03, 14.80), 2 (9.15, 16.68) and 3 (9.48 and 19.87) give an estimate of 68% keto form of 2 under the assumption that HBQ is fully in the enol form and 3 exists as a keto form only. Unfortunately the interpretation of the UV-Vis spectra in DMF is not straightforward.…”

“…In compounds 2 and 3, the ground and excited state proton transfer is investigated as a consequence of incorporating a strong electron acceptor(s), 23 while in compounds 4 and 5 the inuence of competitive processes takes our attention. In the case of 4, the incorporation of an azo group creates an alternative tautomeric route (azo-quinonehydrazone, Scheme 2) to the HBQ type proton transfer.…”