ABSTRACT
I. Introduction ...................................................................................................................... 232
A. Single-and Double-Well H-Bonds.......................................................................... 232
B. Low-Barrier H-Bonds, Short, Strong H-Bonds, “Symmetric” H-Bonds ................ 232
1. Resonance-Assisted H-Bonds, Charge-Assisted H-Bonds ............................... 233
2. Sterically Enforced H-Bonds ............................................................................ 233
II. Computational Work........................................................................................................ 234
A. Energetic and Geometric Descriptions .................................................................... 234
B. Accounting for Solvation......................................................................................... 235
III. Methods of Observation................................................................................................... 236
A. Measurement of pK
................................................................................................ 237
B. Fractionation Factors................................................................................................ 237
C. NMR Chemical Shifts.............................................................................................. 238
D. NMR Coupling Constants........................................................................................ 239
E. Infrared (IR) ............................................................................................................. 240
F. X-Ray and Neutron Diffraction ............................................................................... 240
IV. Current Work ................................................................................................................... 241
A. Intramolecular Systems............................................................................................ 241
1. Enol Tautomers of b-Dicarbonyls and Related Molecules.............................. 241
2. Proton Sponge ................................................................................................... 242
3. Dicarboxylic Acids............................................................................................ 243
4. Schiff Bases ....................................................................................................... 244
B. Intermolecular Systems............................................................................................ 245
1. Pyridine-Acid Complexes................................................................................ 245
2. Enzymes............................................................................................................. 246
V. Conclusion........................................................................................................................ 247
Acknowledgments ........................................................................................................................ 247
References..................................................................................................................................... 247
Hydrogen bonds (H-bonds) create the stabilizing interactions between a donor, typically a hetero-
atom such as N or O bearing a hydrogen, and an acceptor, typically a heteroatom bearing a lone
pair. A common convention is to represent the donor as A-H and the acceptor as B, so that the
H-bond is represented as a dashed bond: A-H· · ·B.
