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Keto Tautomer → Enol Tautomer. In the first step, a base removes an α-hydrogen from a carbonyl containing compound to form an alkene by an E 2 like process. The causes the pi electrons of the carbonyl bond to move onto the carbonyl oxygen to form an enolate anion.
The degradation of serine, for example, involves an enamine to imine tautomerization step, followed by hydrolysis of the imine (section 11.6) to form pyruvate. As we shall see in a later section, enamines are key intermediates in a very important type of carbon-carbon bond-forming reaction.
Keto–enol tautomerism of carbonyl compounds is catalyzed by both acids and bases. Acid catalysis occurs by protonation of the carbonyl oxygen atom to give an intermediate cation that loses H + from its α carbon to yield a neutral enol (Figure 22.2a).
Under basic conditions, the enolate tautomer forms. Both the enol and enolate are nucleophiles that can undergo subsequent reactions. The mechanism for both acidic and basic reaction conditions are shown below. Acid conditions. 1) Protonation of the Carbonyl. 2) Enol formation. Basic conditions. 1) Enolate formation. 2) Protonation.
21 cze 2022 · The enol tautomer is nucleophilic on the carbon adjacent to the C-OH bond (the “alpha-carbon”) and undergoes reactions with electrophiles; Keto-enol tautomerism can be catalyzed with acid or base. Generally the keto tautomer is favored at equilibrium.
Draw the corresponding keto or enol tautomer for each of the following molecules. Predict the product (s) and show the mechanism for each of the following reactions: The following two optically active β -keto acids were decarboxylated under the conditions typically used for the acetoacetic ester synthesis.
• enolates are ambident nucleophiles and can react at either oxygen or carbon terminus. • SOFT electrophiles ( e.g. most carbon electrophiles) tend to react at carbon (soft centre). • HARD electrophiles tend to react at oxygen (hard centre).
