Malonic acids substituent effect

The protons attached to C 2 of malonic acid are not directly involved m the process and so may be replaced by other substituents without much effect on the ease of decar boxylation Analogs of malonic acid substituted at C 2 undergo efficient thermal decar boxylation... 

Although the reaction mechanism of this type of reactions is not fully elucidated, it is easily anticipated that no intramolecular special stabilization effect for the carbanion generated from decarboxylation is expected, different from the case of malonic acid-type compounds. Moreover, cinnamic acid derivatives that have both the electron-donating and withdrawing substituents have been reported to undergo this reaction. This fact suggests that the enzyme itself stabilizes the transition state without the aid of mesomeric and inductive effects of the other part of the substrate molecule itself. If such unknown mechanism also works for other... 

Note that the primary effect of the alkyl substituents is steric, rather than electronic, with only branching on the carbon attached to the parent malonic acid effective in closing the jaws to strengthen the intramolecular hydrogen bond. Taking the "melting of one water molecule from the dianion to contribute... 

The product of a malonic ester synthesis is a substituted acetic acid, with the substituent being the group used to alkylate malonic ester. In effect, the second carboxyl group is temporary, allowing the ester to be easily deprotonated and alkylated. Hydrolysis and decarboxylation remove the temporary carboxyl group, leaving the substituted acetic acid. 

In octanoic acid solvent, alkyl substitution of malonic acids causes a small decrease in AG and thus an increase in rate as seen from Table 47. This is in contrast to the alkyl substituent effect in water (Table 46). The enthalpy of activation is clearly more favorable for decarboxylation of alkyl malonic acids than malonic acid in octanoic acid. Both Ai/ and AG are less favorable for decarboxylation of malonic acid in octanoic acid compared to water. This is expected on the basis of either the concerted (2) or the zwitterion mechanism (3) and (4). Association of the carboxyl groups of malonic acid with the octanoic acid solvent would thwart the attainment of the concerted transition state. Also generation of the zwitterion would be suppressed in octanoic acid. It is clear that additional work is required... 

Many substituted thiophenes are commercially available. Thus, the study of the effects of substituents on polythiophene is relatively straightforward in comparison with pyrrole, whose 3-monosubstituted and 3,4-substituted derivatives are not easily synthesized. Table 3 gives many substituted thiophenes that can be electrochemi-cally oxidized to produce conducting polymers. Some derivatives, such as 3-thiophene acetic acid, 3-thiophene malonic acid, 3-thiophene carboxylic acid, and 3-thiophene carboxaldehyde do not polymerize at all [205). 

The carbon nucleophiles in amine-catalyzed reaction conditions are usually rather acidic compounds containing two electron-attracting substituents. Malonic esters, cyanoacetic esters, and cyanoacetamide are examples of compounds which undergo condensation reactions under Knoevenagel conditions.115 Nitroalkanes are also effective nucleophilic reactants. The single nitro group sufficiently activates the a hydrogens to permit deprotonation under the weakly basic conditions. Usually, the product that is isolated is... 

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