Alpha Substitution

Iron carries half the charge of a whole electron. The calculation produces a set of molecular orbitals appropriate for this pseudowave function. HyperChem then assigns the unpaired electron its proper spin (alpha), substitutes this electron in the orbital formerly occupied by the half electrons, and calculates energy and other properties. 

Both in the laboratory and in living organisms, the reactions of carbonyl compounds take place by one of four general mechanisms nucleophilic addition, nucleophilic acyl substitution, alpha substitution, and carbonyl condensation. These... 

The third major reaction of carbonyl compounds, alpha substitution, occurs at the position next to the carbonyl group—the alpha (a) position. This reaction, which takes place with all carbonyl compounds regardless of structure, results in the substitution of an a hydrogen by an electrophile through the formation of an intermediate enol or enolcite ion ... 

Alpha-substitution reactions occur at the position next to the carbonyl group—the a position—and involve the substitution of an cv hydrogen atom by an electrophile, E, through either an enol or eriolate ion intermediate. Let s begin by learning more about these two species. 

Reactivity of Ends The Mechanism of Alpha-Substitution Reactions 84... 

G Loss of a proton from oxygen yields the neutral alpha-substitution product as a new C=0 bond is formed. 

There is no simple answer to this question, but the exact experimental conditions usually have much to do with the result. Alpha-substitution reactions require a full equivalent of strong base and are normally carried out so that the carbonyl compound is rapidly and completely converted into its enolate ion at a low temperature. An electrophile is then added rapidly to ensure that the reactive enolate ion is quenched quickly. In a ketone alkylation reaction, for instance, we might use 1 equivalent of lithium diisopropylamide (LDA) in lelrahydrofuran solution at -78 °C. Rapid and complete generation of the ketone enolate ion would occur, and no unreacled ketone would be left so that no condensation reaction could take place. We would then immediately add an alkyl halide to complete the alkylation reaction. 

Yuki, H. and Hatada, K. Sterospecific Polymerization of Alpha-Substituted Acrylic Acid Esters. Vol. 31, pp. 31, pp. 1—45. 

Richard, J. P. Amyes, T. L. Bei, L. Stubblefield, V. The effect of beta-fluorine substituents on the rate and equilibrium-constants for the reactions of alpha-substituted 4-methoxybenzyl carbocations and on the reactivity of a simple quinone methide. J. Am. Chem. Soc. 1990, 112, 9513-9519. 

Table III. PE and RIE results for alpha-substituted polyacrylates -(CH2-C(X)C02CH3>.

The market potential of such high-tech materials and engineering plastics is not quite clear. An essentially shorter time-to-market is to be expected with pharmaceutical (intermediate) products. Examples are dipeptides containing alpha-substituted amino acids [65] and d,l-phenylalanine [66]). 

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