GAS AND SOLUTION-PHASE NMR-STUDIES OF N-ETHYLMORPHOLINE INTRAMOLECULAR AND INTERMOLECULAR EFFECTS ON RING INVERSION RATE CONSTANTS

Temperature dependent gas phase H-1 NMR spectra of N-ethylmorpholine are consistent with the following activation parameters for the ring inversion process: DELTAG(double dagger) = 47.7 (0.3) kJ mol-1, DELTAH(double dagger) = 47.1 (2.3) kJ mol-1, DELTAS(double dagger) - 1.9(4.9) J mol-1 K-1, E(act) = 49.2(2.3) kJ mol-1 and A(infinity) = 1.2(0.4) x 10(13) S-1. Rate constants in the gas phase and in CDCl3 Solution are very similar while those obtained in CS2 solutions are almost twice as large at corresponding temperatures. Rate constants obtained for a 1% solution of N-methylmorpholine in CDCl3. obtained in the present study and those previously obtained in the gas phase and CS2 solutions show a similar trend. The observed phase and solvent dependent rate constants do not agree with predictions based on simple steric or dielectric considerations and may indicate that complex static and dynamic solvent effects are important in the liquid solutions.