Rodham, David A. and Suzuki, Sakae and Suenram, Richard D. and Lovas, Frank J. and Dasgupta, Siddharth and Goddard, William A., III and Blake, Geoffrey A. (1993) Hydrogen bonding in the benzene–ammonia dimer. Nature, 632 (6422). pp. 735-737. ISSN 0028-0836 http://resolver.caltech.edu/CaltechAUTHORS:20120914-115237350
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AMINES have long been characterized as amphoteric (acting as both donor and acceptor) in terms of their hydrogen-bond interactions in the condensed phase. With the possible exception of (NH_3)_2, however, no gas-phase complexes exhibiting hydrogen-bond donation by ammonia, the ‘simplest amine’, have been observed. Here we present high-resolution optical and microwave spectra of the benzene–ammonia dimer in the gas phase, which show that the ammonia molecule resides above the benzene plane and undergoes free or nearly free internal rotation. In the vibrationally averaged structure, the C_3 symmetry axis of NH_3 is tilted by about 58° relative to the benzene C_6 axis, such that the ammonia protons interact with the benzene π-cloud. Our ab initio calcula-tions predict a 'monodentate' minimum-energy structure, with very low barriers to rotation of ammonia. The larger separation of the two molecular components, and the smaller dissociation energy, relative to the benzene–water dimer reflect the weak hydrogen-bond donor capability of ammonia, but the observed geometry greatly resembles the amino–aromatic interaction found naturally in proteins.
|Additional Information:||© 1993 Nature Publishing Group. Received 11 January, accepted 9 March 1993. We gratefully acknowledge support from the Caltech Beckman Institute (to W.A.G.) NSF, NASA and the David and Lucille Packard Foundation (to G.A.B.).|
|Official Citation:||Hydrogen bonding in the benzene–ammonia dimer 735 David A. Rodham, Sakae Suzuki, Richard D. Suenram, Frank J. Lovas, Siddharth Dasgupta, William A. Goddard III & Geoffrey A. Blake doi:10.1038/362735a0|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||14 Sep 2012 19:13|
|Last Modified:||14 Sep 2012 19:13|
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