15min:

BARBARA M. GIULIANO, ASSIMO MARIS, SONIA MELANDRI, LAURA B. FAVERO, LUCA EVANGELISTI AND WALTHER CAMINATI, Dipartimento di Chimica "G. Ciamician" dell'Università, Via Selmi 2, I-40126 Bologna, Italy.

We studied the rotational spectra of the adducts of ammonia with several organic molecules, namely tert -butanol, glycidol, ethyl alcohol, anisol and 1,4-difluorobenzene. The adducts with glycidol and ethanol have been observed for both conformers of the substrate molecule. Based on the rotational and ¹⁴N quadrupole coupling constants of the various complexes, we found a considerably different behaviour of ammonia, with respect to water, in its proton donor/acceptor double role. In the interaction with the three alcohol molecules, NH₃ acts as a proton acceptor and the OH groups as a proton donor. However, in the case of glycidol-NH₃, a secundary N-H O interaction occurrs between ammonia and the ether oxygen. This interaction generates a sizable V ₃ barrier to the internal rotation of the NH₃ moiety, while NH₃ undergoes a free rotation in tert -butanol-NH₃ and in ethanol-NH₃. As to the anisole-NH₃ and 1,4-difluorobenzene-NH₃ complexes, the NH₃ group explicits its double proton donor/acceptor role, although through two weak (C_Me-H N and N-H ) H-bonds. There is, however, an important difference between the two complexes, because in the first one NH₃ lies out of the aromatic plane, while in the second one it is in the plane of the aromatic ring.