Aggregation and C−N Rotation of the Lithium Salt ofN,N-Dimethyldiphenylacetamide

[GRAPHICS] Two methyl H-1 NMR signals for the Li salt of N,N-dimethyldiphenylacetamide are observed at low temperature and assigned to the monomer and dimer. From line shape analysis, the dimerization constant (K-1,K-2) is 40 +/- 10 M-1 at 200 K (Delta G degrees = 1.5 kcal mol(-1), Delta H degrees = 0.8 kcal mol(-1), Delta S degrees = 12 eu) and the activation parameters are Delta H-double dagger = 5.5 kcal mol(-1) and Delta S-double dagger = -18 eu. The C-N bond rotation is too fast to observe on the NMR time scale, indicating a rotation barrier of less than 10 kcal mol(-1).