Carboxylic acids are acidic due to the stability of the resonance hybrid carbanion.
Hydrogens attached to carbon atoms immediately adjacent to a carbonyl carbon (a hydrogens) are acidic for the same reason.
In contrast, acid catalyzed halogenation does not involve a carbanion but rather a carbonium ion. not involve a carbanion but rather a carbonium ion.
The carbonyl carbon is subject to nucleophillic attack due to the ability of the intermediate to accommodate a negative charge.
Carbonyl compounds under basic conditions form a carbanion with nucleophillic character.
This nucleophile can now add to the carbonyl carbon to form a b hydroxy carbonyl compound.
So, acetone gives 4-hydroxy-4-methyl-2-pentanone also known as diacetone alcohol.
The Aldol product can undergo dehydration.
So, diacetone alcohol gives 4-methyl-3-penten-2-one (mesityl oxide).
Triphenylphosphine reacts with alkyl halides to form an ylide.
The ylide can be represented by the following two resonance structures and has a carbanion like character.
The ylide can react as a nucleophile towards a carbonyl carbon to form a betaine.
The betaine goes on to form a new compound where the original =O group has been replaced by a = CR1R2 group.
In the presence of an alkoxide ion the a hydrogen of a carboxylic acid ester is abstracted to form a carbanion.
This carbanion is a nucleophile which can in turn attack the carbonyl carbon of the same or different carboxylic acid ester
The resulting intermediate loses an alkoxide ion. In the reaction mixture (strongly basic due to the presence of the alkoxide ion) the product is present as the following very stable carbanion.
Upon acidification a b-keto ester is formed.
Acetoacetic ester is one important b-keto ester.
In this reaction Zinc is reacted with an a bromo ester to form a nucleophile
This intermediate can then react with the carbonyl carbon of an aldehyde or ketone to form an intermediate which upon acidification yields a b-hydroxy ester.
The reaction product can be dehydrated to form a, b unsaturated esters which can be hydrogenated and then hydrolyzed to form carboxylic acids.
Reaction of sodiomalonic ester with an alkyl halide gives an alkylmalonic ester.
The alkylmalonic ester can be further reacted with sodium ethoxide and the resulting salt reacted with an alkyl halide to form a dialkylmalonic ester.
The esters can be hydrolyzed to the malonic acids. Acid and heat forms a substituted acetic acid.
Reaction of sodioacetoacetic ester with an alkyl halide gives an alkylacetoacetic ester (aka an ethyl alkylacetoacetate).
The alkylacetoacetic ester can be further reacted with sodium ethoxide and the resulting salt reacted with an alkyl halide to form a dialkylacetoacetic ester.
The esters can be hydrolyzed to the corresponding acids acids. Acid and heat (sometimes not necessary) causes decarboxylation to form ketones
A protective group for the carboxyl functionality.
The best base is
A good alkylborane can be prepared by the following scheme: