Aluminum-hydrogen bond, nucleophilic

Alkyl methacrylates, hydrolysis of polymeric ester functionality, 259 Aluminum-hydrogen bond, nucleophilic substitution, 264 Amines alkylation, 28 benzyl-group cleavage, 25 Aminomethylation chloromethylated polymers, 19 Deltfpine reaction, 19 Anionic polymerization advantages, 85... 

The concept that by carrying out a surface analysis on a model specimen one can obtain direct access to the interphase chemistry is a potentially very exciting and rewarding idea. The interaction of PMMA with various metals (as exemplified hyO Fig. 10.14 above) has been studied in some detail using high resolution XPS (Leadley and Watts 1997). In this work the manner in which PMMA formed specific interactions with oxidized metal surfaces was studied by the nature of the fine structure in the XPS spectrum. In this manner, it was possible to show that the polymer formed hydrogen bonds with oxidised silicon (an acidic substrate), a bidentate structure with oxidised aluminum (an amphoteric substrate) and would undergo acyl nucleophilic attack with oxidised nickel (a basic substrate). 

The different reactivities of the two substituents on C-l allow selective replacement and conversion of them. Alkyl monothio-acetals [proposed as intermediates in mercury(II)-catalyzed demer-captalation reactions—see Section IV,l,b] have been prepared from a-bromothioethers by the combined action of an alcohol and silver(I) carbonate the introduction of S-nucleophiles is discussed in Section 11,6. Reduction of 81 by lithium aluminum hydride effects hydrogen-olysis of the carbon-halogen bond, whereas the action of Raney nickel on the derived S-ethyl O-methyl monothioacetal specifically cleaves the carbon-sulfur bond to afford the pentaacetate of 1-0-methyl-D-galactitol.327... 

The most common metal hydrides used to reduce carbonyl compounds are lithium aluminum hydride (LiAlHJ and sodium borohydride (NaBH4). The metal-hydride bond is polarized, with the metal positive and the hydrogen negative. Therefore, the reaction involves irreversible nucleophilic attack of the hydride (H ) at the carbonyl carbon ... 

Another standard example is the nucleophilic attack by lithium aluminum hydride (LAH) on a ketone or aldehyde (Scheme 10.8). Each hydrogen in LiAlH4 is partially negatively charged, and therefore the Al-H a bonds are nucleophilic. After the nucleophilic attack by hydride, the resulting alkoxide anion coordinates with the A1 species. These two steps are repeated three more times. Finally, dilute acid is added to supply a proton to the alkoxide anion (electron pushing not shown). 

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