Hydrogen carbonate dimer

Anionic Rosette Ribbon Built of Guanidinium and Hydrogen Carbonate Dimer... 

Electrochemical oxidation of 2,6-dimethoxy-4-allylphenol in aqueous methanol buffered with sodium hydrogen carbonate gives similar amounts of 2- and 4-methoxy substitution products, fhe 2-methoxylated product readily undergoes a Diels-Alder reaction with itself. The dimer 19, the natural product asatone, is found in some 1 % yield and most of the 2-methoxylated product is lost by addition of the ally alkene bond across the diene system of a second molecule [109]. 

Many carboxylic acids exist in the free state as hydrogen-bonded dimers with an oxygen-oxygen separation (between oxygens linked to the same carbon atom) close to 220 pm. Replacement of these hydrogens by two metal atoms results in the close approach of the two metal atoms.28 Much of the interest in these dinuclear paddlewheel systems has been generated by a need to understand the nature of these metal-metal interactions. The natural desire of chemists is to use formal bond orders as an index of this interaction and much has been published to this end. However, there are growing indications that such a formal concept is not entirely appropriate for such systems.29... 

In 5-hydroxy-3-phenyl-l,2,4-oxadiazole (97a) the keto forms (97b, c) predominate due to the proximity of the electronegative oxygens at the sp2 carbon. Of these three tautomers (97c) is favored by IR, UV and NMR spectral data (76BSB35). The tautomer (98b) is more important in the 5-phenyl isomer in solution. Nevertheless the position of tautomeric equilibrium in the two cases is dependent on solvent. For example, in the solid (98b, c) predominates but in acetone and other oxygen solvents (98a) allows for an effective hydrogen bonded dimer (99). 

Thermosynechococcus (T.) vulcanus crystallizes as a dimer (Figure 3.4.2) that contains about 2,800 solvent water molecules [7], Each monomer consists of about 20 protein subunits that harbor 77 cofactors 35 chlorophylls (Chi a) 11 p-carotenes 2 plastoquinones (PQ) 2 pheophytines (Pheo a) 1 Mn4OsCa complex 2 heme Fe 1 nonheme Fe and 1 hydrogen carbonate, HCO3/CO3. The overall reaction of PSII is that of a light-driven water plastoquinone oxidoreductase [1] ... 

Hobza, R, Sponer, J., and Polasek, M., H-honded and stacked DNA base pairs cytosine dimer. An ab initio second-order M0ller-Plesset study, J. Am. Chem. Soc. 117, 792-798 (1995). McDowell, S. A. C. and Buckingham, A. D., Isotope effects on the stability of the carbon monoxide-acetylene van der Waals molecule and the hydrogen fluoride dimer, Chem. Phys. Lett. 182, 551-555 (1991). 

Zeng, Y. R, Sharpe, S. W., Shin, S. K., Wittig, C., and Beaudet, R. A., Infrared spectroscopy of C02 D(H)Br Molecular structure and its reliability, J. Chem. Phys. 97, 5392-5402 (1992). Muenter, J. S., Potential functions for carbon dioxide-hydrogen halide and hydrogen halide dimer van der Waals complexes, J. Chem. Phys. 103, 1263-1273 (1995). 

Under high-pressure conditions, volatile species, such as hydrogen, carbon dioxide, and in some cases olefins or alkanes, are accumulated on the anode surface, which may affect the product distribution [33,36]. An aqueous Kolbe electrolysis of an alkanoic acid (in the range C4-C6) tends to give higher yields of the Kolbe dimers when run at elevated pressure (100 kPa) than an equivalent experiment at atmospheric pressure. 

The hydrogen carbonate XHCO3 family with X = Na, K, Rb, Cs is interesting in the context of both supramolecular engineering and HB studies, because it gives a series of ionic compounds with hydrogen-bonded dimers... 

Among the AHCO3 compounds, only potassium hydrogen carbonate KHC03 was systematically studied as a function of temperature. In the high-temperature phase with one dimer per unit cell, the protons are dynamically disordered in a symmetric double-minimum potential. A nonferroic structural phase transition occurs at Tc = 318 K, and the unit cell is doubled with two inequivalent dimers. Incoherent neutron scattering experiments123 proved that the double-well potential associated to the two dynamically disordered tautomers becomes asymmetric in the low-temperature phase. This phase transition has thus an order-disorder character, and can be described by an order parameter Ap = p —p2, which measures the difference of occupation probabilities of the two sites. 

EXPLOSION and FIRE CONCERNS extremely flammable gas gas is heavier than air and may travel along the ground distant ignition possible forms explosive gas/air mixtures substance may readily polymerize reacts with water to form acetic acid violent reaction with many organic compounds NFPA rating (not rated) rapidly forms explosive diacetyl peroxide upon interaction with hydrogen peroxide dimerizes to diketene even at low temperatures toxic gases and vapors, such as carbon monoxide, may be released in a fire use dry powder or carbon... 

---