Hindered internal rotation in [15N]trifluoroacetamide

Abstract

The lH n.m.r. spectrum of [15N] trifluoroacetamide has been measured in dioxan and methyl propyl ketone from 15 to 80 "C. From the temperature dependence of the n.m.r. spectra the values for the energy barrier ,Ea to internal rotation about the central C-N bond were determined by means of total line-shape analysis. It has been found that the barrier was almost independent of the nature of the solvents used : €a = 76.5 f 2-9 in dioxan and 77.8 f 2.5 kJ mol-l in methyl propyl ketone. The other thermodynamic activation parameters AGZ (298 K), AH$' and A S were calculated to be 74.0.74.5, and 2.1 in dioxan and 73.6 kJ mol-l, 74.5 kJ mol-l, and 3.3 J m o l -l K -I in methyl propyl ketone. The results obtained are compared with those for related compounds.

Gas-Phase Nuclear Magnetic Resonance Study of (15N)Trifluoroacetamide: Comparison of Experimental and Computed Kinetic Parameters

“…Previously, Ouchi et al determined the following kinetic parameters ( κ = 0.5) for ( 15 N)TFA in dioxane (16 mol %) and methyl propyl ketone (18 mol %): Δ G ⧧ 298 = 17.3(0.7) kcal mol -1 , Δ H ⧧ = 17.8(0.8) kcal mol -1 , and Δ S ⧧ = −0.9(2.3) cal K -1 mol -1 and Δ G ⧧ 298 = 17.2(0.6) kcal mol -1 , Δ H ⧧ = 17.8(0.8) kcal mol -1 , and Δ S ⧧ = −0.7(0.2) cal K -1 mol -1 for the two solvents, respectively. The gas-phase values determined in this study are Δ G ⧧ 298 = 15.1(0.36) kcal mol -1 , Δ H ⧧ = 13.3(1.3) kcal mol -1 , and Δ S ⧧ = −5.9(4.5) cal mol -1 K -1 .…”