Dynamic 1H NMR Study of the Hindered Internal Rotation in a Particular Biological Phosphorus Ylide Involving 6-Azauracil

Sayyed Mostafa Habibi-Khorassani*¹, Mehdi Shahraki¹, Malek Taher Maghsoodlou¹, Eideh Mofarrah¹, Elham Mofarrah² and Sayyed Rasul Mousavi¹

¹Department of Chemistry, University of Sistan and Baluchestan, P. O. Box 98135-674, Zahedan, Iran, ²Department of Chemical Engineering, Amirkabir University of Technology (Tehran Polytechnic), Tehran, Iran

Abstract: The hindered internal rotations around the partial carbon-carbon double bond (MeO₂C↑=CPPh₃), nitrogen-carbon (N↑-C-CH) and carbon-carbon single (MeO₂C↑H-C-C=PPh₃) bonds within dimethyl-2-(6-Aza uracil 1-yl)-3-(triphenylphosphoranylidene) butandioate has been experimentally studied by the dynamic ¹H NMR spectroscopic in variable temperatures. The activation (∆H^‡, ∆S^‡, ∆G^‡) and kinetic (k_c, E_a.) parameters were calculated in a series of separate dynamic ¹H NMR spectra. The energy of activation parameters obtained from classic, Eyring and Arrhenius methods were also compared for carbon-carbon double, this compound. The results from Eyring and Arrhenius plots were in good agreement, however, they were different with the classic method. Rotation around the carbon-carbon single bond ∆G^‡ has low value than rotation around the carbon-carbon double bond and rotation around the carbon-carbon single bond.

Keywords: Dynamic ¹H NMR; Activations Parameters; Internal Rotations; Ylide; Isomerism

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