PHYS 398 |
| A nuclear magnetic resonance (NMR) conformational study of 4,7,13,16,21,24-hexaoxa-1,10-diaza-bicyclo[8.8.8]hexacosane (222) in the crystalline and solution phases is presented with the primary goal of understanding host-guest binding equilibria. Gauge-Independent Atomic Orbital (GIAO) 13C NMR shielding calculations at B3LYP/6-31G* are compared to experimental correlates, and observed differences are interpreted with Natural Bond Orbital (NBO) and Natural Chemical Shielding (NCS) methods. Energy minimized conformers of 222, derived from experimental X-Ray crystallography and theoretical Monte Carlo MMFF conformer searches, possessed chemical shielding similar to that in solution; central carbon atoms were downfield, while carbon atoms primary to the nitrogen bridgeheads were most upfield. Despite the conformational rigidity of the bound 222, shielding differences greater than 2 ppm were observed due in part to the presence of the cation and to the induced conformation of the cryptand backbone.
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Physical Chemistry Poster Session
7:00 PM-9:00 PM, Wednesday, August 22, 2007 BCEC -- Exhibit Hall - B2, Poster
Division of Physical Chemistry |
