ADSORPTION OF THE AMIDES N-ETHYLACETAMIDE AND 2-PYRROLIDINONE ON GAMMA-ALUMINA - INFLUENCE OF THE STEREOCHEMISTRY OF THE ADSORBATE

The adsorption isotherm of 2-pyrrolidinone on gamma-alumina shows an i nitial rapid uptake of solute followed by a plateau. In contrast, N-et hylacetamide gives a gradual increase in adsorption. For both solutes, DRIFTS data indicate that the carbonyl and N-hydrogen functionalities are involved in bonding, and the most probable conformation of N-ethy lacetamide on the surface is as the trans isomer. Theoretical calculat ions show that in the linear molecule the C-N linkage has a marked dou ble bond character, which results in the molecule remaining in the tra ns form. The energies of interaction of the linear and cyclic molecule s with one and two aluminium ''sites'' are calculated. The cyclic mole cule can adsorb on a single surface ''site'' through both functionalit ies. Adsorption of the trans linear molecule on two ''sites'' gives a comparable interaction energy. Though both molecules adsorb sufficient ly strongly from single solute solutions to survive washing, only 2-py rrolidinone is adsorbed from a solution of the two amides, The differe nces in behavior are attributed to the steric restraints for adsorptio n on a real surface.