Tetrahedron p. 3233 - 3240 (1980)
Update date:2022-08-02
Topics:
Nicole, D.
Delpuech, J-J.
Wierzbicki, M.
Cagniant, D.
Two stereoisomers of the title compound are observed by H NMR at 10 deg C.Their spectra coalesce at higher temperature (10 deg C-90 deg C).The equilibrium and rate constants K and k, strongly dependent on the solvent used (1,4-dioxane, tetrahydrofuran, acetone, chloroform); typical values for these parameters and the related thermodinamic functions are: K(25 deg C)=0.170; k(25 deg C)=23.2s-1; ΔHR and ΔH(excit.)=4.94 and 17.9kcal.mol.-1; ΔSR and ΔS(excit.)=13.1 and 7.7 e.u. in a 0.2 molar solution in 1,4-dioxane.The two isomers are shown to result from a hindered rotation around the aryl-to-nitrogen bond, presumably due to a direct resonance effect between the amide and nitro groups.The more abundant isomer was assigned a planar molecular structure in which the O atom of the amide group is close to the S atom of the thiophen ring, presumably on account of an electrostatic interaction between these two atoms which bear partial electrical charges of opposite sign.
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