Oxamide

One of the our original investigations into hydrogen bonding was the hydrogen bonding network of oxamide, see Figure 1. Each oxamide molecule contributes to eight hydrogen bonds; two carbonyls which involve in two hydrogen bonds each, and two amines whose hydrogens are involved in hydrogen bonds. In the crystal a planar, two dimensional network is formed.

Imidazolium Hydrogen Maleate

The study of imidazolium hydrogen maleate (IHM) provides unique insight into the properties of hydrogen bonds. Above all, IHM contains the shortest hydrogen bond yet discovered. The oxygen to oxygen distance in the OH ··· O hydrogen bond is an impressive 2.408 Ångstroms. IHM, as seen in Figure 2, has a unique structure which facilitates study through INS spectroscopy. IHM can be deuterated in multiple combinations to provide imformation about specific vibrational modes. In addition, the fact that IHM crystallizes into isolated tetramers accelerates theoretical modeling.

1,3-Cyclohexanedione

1,3-cyclohexanedione (CHD) has been intriguing on many levels. CHD undergoes keto-enol isomerization and forms linear hydrogen bonded chains in the crystal. Interestingly, phase transistions in the crystal involve the shifting of the hydrogen bonded hydrogen to the nearest neighbor down the whole chain, in a "domino effect". The keto-enol isomerization allows deuteration of most extraneous (not involved in hydrogen bonds) hydrogens. The deuteration process is turns out to be fairly complicated as the keto-enol isomerization process runs along multiple paths, each of which is dependent upon many variable. This includes: concentration, temperature, pH, time, and solvent. Additionally, CHD forms an complex with benzene, in which six CHD molecules for a hydrogen bonded host ring with a benzene molecule in the center.