# HYDROGEN BONDING IN THE BENZENE-AMMONIA DIMER

Please use this identifier to cite or link to this item: http://hdl.handle.net/1811/18617

Files Size Format View
1993-TC-09.jpg 84.70Kb JPEG image

 Title: HYDROGEN BONDING IN THE BENZENE-AMMONIA DIMER Creators: Rodham, D. A.; Suzuki, S.; Suenram, R. D.; Lovas, F. J.; Dasgupta, S.; Goddard, W. A., III; Blake, Geoffrey A. Issue Date: 1993 Publisher: Ohio State University Abstract: Amines have long been characterized as amphoteric in terms of their condensed phase hydrogen bond interactions. With the possible exception of $(N H_{3})_{2}$, however, no gas phase complexes exhibiting hydrogen bond donation by ammonia, the simplest amine.'' have been observed [1,2]. High resolution microwave and optical spectroscopy of the benzene-ammonia dimer are presented. The results are consistent with a vibrationally averaged structure where the ammonia resides above the benzene plane experiencing free or nearly free internal rotation. The monomer symmetry axes are tilted by about sixty degrees, such that the ammonia protons interact with the benzene $\pi$-cloud. Ab initio calculations predict a monodentate'' minimum energy structure, with a very low barrier to ammonia proton exchange. The larger monomer separation and smaller dissociation energy relative to benzene-water [3] are illustrative of the weak hydrogen bond donation capability of ammonia, but the observed geometry resembles greatly the amino-aromatic interaction found naturally in proteins [4]. Description: [1] D.D. Nelson. Jr.. G.T. Fraser and W. Klemperer, Science, 238, 1670 (1987). [2] J.G. Loeser et al., J. Chem. Phys., 97, 4727 (1992). [3] S. Suzuki et al., Science, 257, 942 (1992). [4] S.K. Burley and G.A. Petsko, FEBS Lett., 203, 139 (1986). Author Institution: Division of Chemistry and Chemical Engineering, California Institute of Technology.; Molecular Physics Division, National Institute of Standards and Technology; Materials and Molecular Simulations Center, Beckman Institute, California Institute of Technology; Division of Geological and Planetary Sciences, California Institute of Technology URI: http://hdl.handle.net/1811/18617 Other Identifiers: 1993-TC-9