Hydrogen anion, confined

The anion confinement by the receptor was further confirmed by single crystal X-ray analyses in the solid state. In the structure, the anion remains in proximity to the TMA cation, and is symmetrically bound by all four -NH amide hydrogen bonds (Fig. 11.13). Additionally, from the top, four aromatic hydrogens (from ort/jo-positions) are in close proximity to the chloride (C-H Cl distances are 2.7-3.1 A). This weak interaction also adds to the overall binding efficiency and selectivity. Indeed, it is seen that the anion effectively seals this molecular capsule. The view from the top (Fig. 11.13) also reveals the space/void to which the anion is embedded and isolated from the environment by the bulky phenyl groups [34]. 

DOT CLASSIFICATION 4.3 Label Dangerous When Wet SAFETY PROFILE The toxicity of potassium compounds is almost always that of the anion, not of potassium. A dangerous fire hazard. Metallic potassium reacts with moisture to form potassium hydroxide and hydrogen. The reaction evolves much heat, causing the potassium to melt and spatter. The reaction also ignites the hydrogen, which burns, or if there is any confinement. 

A possible isomerization pathway for the = 6 cluster has been proposed on the basis of the quantum chemical calculations of Conbariza et al. [59] and Kim et al. [33]. In the predicted most stable structure for the ground state [59], the 1 ion lies on the surface of a V-shaped solvent network. It has been assumed that the initially excited state has a similar geometry, in which the excess electron is weakly bound by the net dipole moment of the solvent network. The supposed form after isomerization resembles the stable half-cage structure for the water hexamer anion [33], in which the excess electron is confined by dangling hydrogens of waters. 

The Clemmensen reduction of aldehydes and ketones to methyl or methylene groups takes place by heating with zinc and hydrochloric acid. A non-miscible solvent can be used and serves to keep the concentration in the aqueous phase low, and thus prevent bimolecular condensations at the metal surface. The choice of acid is confined to the hydrogen halides, which appear to be the only strong acids whose anions are not reduced with zinc amalgam. The Clemmensen reduction employs rather vigorous conditions and is not suitable for the reduction of polyfunctional molecules, such as 1,3- or 1,4-diketones, or of sensitive compounds. However, it is effective for simple compounds that are stable to acid (7.38). A modification under milder conditions uses zinc dust and HCl dissolved in diethyl ether (ethereal HCl). Other methods for converting C=0 to CH2 are described in Schemes 7.87 and 7.105. 

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