The Hindered Internal Rotations in a Particular Phosphorane Involving a 6-aza Thiothymine: An Experimental Dynamic 1H NMR Study with Three Methods of Determining Activation Parameters

Abstract

The hindered internal rotations around the partial carbon-carbon double bond (MeO 2 C=CPPh 3 ), nitrogen-carbon (N-C-CH) and carbon-carbon single (MeO 2 CH-C-C=PPh 3 ) bonds within the dimethyl-2-(6-aza thiothymin-1-yl)-3-(triphenyl-phosphoran ylidene) butandioate has been experimentally studied by the dynamic 1 H nuclear magnetic resonance (NMR) spectroscopic in variable temperatures. The activation (DH à , DS à , DG à ) and kinetic (k c , E a ) parameters were calculated in a series of separate dynamic 1 H NMR spectra. The energy of activation parameters obtained from classic, Eyring and Arrhenius methods were also compared. The results from Eyring and Arrhenius plots were in good agreement; however, were slightly different from the classic method.

Assignment of the Major Geometrical Isomer of the Synthesized Stable Phosphorus Ylide: Crystallography and Theoretical Approaches

“…1.). On the other hand, the structural assignments of the Zisomer as a major form have previously been reported for other phosphorus ylides 22,15 . Herein the 1 H NMR spectrum of ylide 4 exhibited two singlets at 0.97 and 1.57 ppm arising from the two tert-butoxy groups; this only occurs for the Z-isomer of ylide 4 because of the tert-butoxy group (at 0.97 ppm) is shielded due to the anisotropic effect of a phenyl group of triphenylphosphine.…”

“…These ylides usually exist as a mixture of the two geometrical isomers, although some ylides exhibit one geometrical isomer. Assignment of the two Z-and E-isomers are possible by some experimental methods such as 1 H, 13 C NMR, IR spectroscopy, mass spectrometry and elemental analysis data [13][14][15][16]. In order to gain a better understanding of the major isomer, the crystal structure of di-t-butyl-(N-2-indolinone-1-yl)-3-(triphenylphosphoranylidene) succinate was determined by X-ray crystallography.…”

Investigation of rotations in isomerism forms of a ylide of theophylline: Dynamic 1H NMR study

“…Theophylline in structure of ylides has significant dynamic 1 H NMR effects. So, these effects afford important information regarding the rotational isomers 2,[20][21][22][23][24][25] .…”