Magnesium atoms, reactions

You know from Investigation 10-A that magnesium metal, Mg(s), displaces aluminum from an aqueous solution of one of its compounds, such as aluminum nitrate, Al(N03)3(aq). To obtain a balanced net ionic equation for this reaction, you can start by looking at tbe half-reactions. Magnesium atoms undergo oxidation to form magnesium ions, which have a 2+ charge. The oxidation half-reaction is as follows. 

The loss of electrons by magnesium atoms to form Mg cations indicates that this reaction between magnesium metal and hydronium ions involves oxidation and reduction. An atom of magnesium is oxidized, losing two electrons to form a Mg + cation. Because electrons must be conserved in every chemical process, electrons lost by Mg must be gained by some other species. In this example the electrons lost by Mg are gained by H3 O , which is reduced to form H2 and H2 O. 

Magnesium atoms are oxidized in this reaction, so some other species must be reduced. Oxygen molecules accept the electrons lost by the magnesium atoms. Each oxygen atom gains two electrons from a magnesium atom, generating two oxide anions O2 + 4 e 2 O... 

In this reaction, each of the two magnesium atoms donates two electrons to the two oxygen atoms making up the oxygen molecule. In the process, each magnesium atom becomes Mg + and each oxygen atom becomes... 

From the reaction of the radical anion of l,2-bis[(2,6-diisopropylphenyl)imino]acen-aphthene (dpp-bian) with i -PrMgCl, the persistent radical complex isopropylmagnesium dpp-bian (253) was isolated in yields up to 60% (equation 20). An X-ray crystal-structure determination of 253 showed that the magnesium atom has distorted tetrahedral coordination geometry as the result of the cr-bonded isopropyl group, one coordinate-bonded diethyl ether molecule and A, A -chelate bonding of the dpp-bian radical anion. The radical anionic character of the dpp-bian moiety is indicated by the relatively long Mg—N bond distances [Mg-N 2.120(2) and 2.103(2) A]. 

A. Reactions of Magnesium Atoms with Organic Substrates. 157... 

The enolate structure of 17 is deduced from the IR data of the reaction medium as a result of the presence of absorption bands at 1490 cm for the C=C bond and 1665 cm for the C=0 bond of the ester group, characteristic for an internal coordination of the enolate magnesium atom with the ester C=0 . 

Other chiral magnesium enolates derived from amides are known to react with aldehydes. For example, the aldol-type reaction of magnesium enolate of —)-trans-2-N,N-diethylacetamide-l,3-dithiolanes-5 -oxide with isobutyraldehyde affords a single diastere-omer in 82%. The relative stereochemistry of the adduct originates from a rigid transition state 87 where the oxygen atoms of the enolate and the aldehyde are coordinated to the magnesium atom. ... 

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