Rate constants obtained from total line-shape analysis of 11 temperature-dependent gas-phase NMR spectra of (N-15)trifluoroacetamide yielded the following kinetic parameters: Delta G(298)double dagger = 15.1(0.36) kcal mol(-1), Delta H double dagger = 13.3(1.3) kcal mol(-1), and Delta S double dagger = -5.9(4.5) cal mol(-1) K-1. Ab initio calculations performed at the MP2 level using the 6-311++G(d,p) basis set calculated Delta G(298)double dagger = 15.19 kcal mol(-1), Delta H double dagger = 14.35 kcal mol(-1), and Delta S double dagger = -2.82 cal mol(-1) K-1 in reasonable agreement with experiment. Hartree-Fock calculations using that basis set were also in reasonable agreement with experiment, yielding Delta G(298)double dagger = 16.03 kcal mol(-1) Delta H double dagger = 14.35 kcal mol(-1), and Delta S double dagger = -5.62 cal mol(-1) K-1. DFT calculations (B3-PW91) using the same basis set gave results that were considerably less accurate.