Magnesiums carbon—hydrogen bonds

Another reaction in which the cleavage of a carbon-hydrogen bond is important is the bromination of ketones. In the bromination of ethyl acetoacetate and 2-carboethoxycyclopentanone, it was shown that multivalent cations are catalysts. In the latter reaction, cupric, nickelous, lanthanum, zinc, plumbous, manganous, cadmium, magnesium, and calcium ions were effective (45). One can interpret the effect of the metal ion in terms of its catalysis of the proton transfer from the ester to a base, whether the reaction is carried out in dilute hydrochloric acid solution (acid-catalyzed bromination) or in acetate buffer (base-catalyzed bromination). 

The application of organometallic compounds or hydrides of the more electropositive main group metals lithium, magnesium or aluminium in organic synthesis, catalysis and polymerization is due to the polarity of the metal/carbon and metal/hydrogen bonds, i.e. to the considerably unsymmetrical electron distribution M —or —respectively. While there are... 

The reaction to be catalyzed poses problems for the enzyme [34]. The abstraction of a proton from an aliphatic carbon atom is generally difficult and slow. The plf of the carbon-bound a-proton of mandelic acid is 22.0 [55], while the p/f the a-proton of the mandelate anion (as for the phenylacetate anion) is approximately 29 [36, 37]. In spite of this, mandelate racemase increases the rate of the racemiza-tion reaction by a factor of 1.7 x 10 to approximately 1000 per second at 25 °C at pH 7 [57, 55]. Interactions of mandelate with enzyme, analogous to those with inhibitor (5)-atrolactate in which one carboxylate oxygen atom is coordinated to the magnesium ion and also hydrogen-bonded to the e-ammonium group of Lysi 64,... 

The acid consumption corresponds to the content of hydrogen carbonates. As well as free HCO3 ions, hydrogen carbonate complexes bonded in ionic pairs with calcium, magnesium, etc. are also determined. 

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