THEORETICAL-ANALYSIS OF SECONDARY KINETIC ISOTOPE EFFECTS IN C-N ROTATION OF AMIDES

The deuterium kinetic isotope effects for rotations about the C-N bond s of formamide, N-methylformamide, and N,N-dimethylformamide have been calculated from, the Bigeleisen equation using the program QUIVER, ba sed upon ab initio harmonic vibrational frequencies for ground states and transition states, calculated with GAUSSIAN 92 at the RHF/6-31G, RHF/6-311++G*, MP2(FC)/6-31G*, and MP2(FC)/6-311++G** levels. The pre dicted isotope effects are similar at the different levels and agree c losely with experimental values from Perrin et al. (J. Am. Chem. Soc. 1992, 114, 8800). The magnitudes of the isotope effects are interprete d.