Journal of Molecular Structure p. 189 - 199 (1997)
Update date:2022-08-10
Topics:
Dziembowska, Teresa
Rozwadowski, Zbigniew
Hansen, Poul Erik
Secondary isotope effects on 13C chemical shifts have been measured in a series quinolinols, quinaldinic acid N-oxides and quinoline-2-carboxyamide N-oxide. For 8-quinolinol N-oxides a good correlation was found between δOH and (n)ΔC(OD) isotope effects. The OH and 13C chemical shifts and (n)AC(OD) show very small temperature dependences. The primary isotope effects are small, positive and temperature insensitive. Furthermore, they increase with increasing (n)AC(OD). All features point towards a localised hydrogen bond in an asymmetric double well potential. The quinaldinic acid N-oxides show long-range isotope effects on 13C chemical shifts of both signs with 2AC=O(OD) rather small. The primary isotope effects of the quinaldinic acid N-oxide is of order of 0.5 ppm, whereas for its 4-ethoxy-derivative is smaller, ~0.3 ppm. The OH chemical shifts resonate at the low field ~ 18-20 ppm and the OH resonance is fairly broad at room temperature, especially for the 4-ethoxy-derivative. The temperature effects on the chemical shifts, primary and secondary isotope effects are small. For quinaldinic acid N-oxides the asymmetric broad quasi-single potential is suggested. For quinoline-2-carboxyamide N-oxide the isotope effects are small, indicating rather weak hydrogen bond.
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