What is Zimmerman Traxler transition state?
In 1957, Howard Zimmerman and Marjorie D. Traxler proposed that some aldol reactions have “six-membered transition states having a chair conformation.” This is now known as the Zimmerman–Traxler model. E-enolates give rise to anti products, whereas Z-enolates give rise to syn products.
Which is the correct statement in aldol condensation reaction?
We know that in aldol condensation, α- hydrogen atoms undergo self- addition between two molecules to form β- hydroxy ketone. Therefore ketone in which α- hydrogen atom is present, give this reaction .
What type of reaction is an aldol reaction?
An aldol condensation is a condensation reaction in organic chemistry in which an enol or an enolate ion reacts with a carbonyl compound to form a β-hydroxyaldehyde or β-hydroxyketone, followed by dehydration to give a conjugated enone.
What is an Enolate in organic chemistry?
Enolates are organic anions derived from the deprotonation of carbonyl compounds. Rarely isolated, they are widely used as reagents in the synthesis of organic compounds.
Which statement about aldol condensation is incorrect?
It accomplishes the formation of a new C—C bond. The enolate is favoured at equilibrium. The key step in the mechanism of base catalysed reaction is attack of α-carbon of an enolate ion on the carbonyl carbo.
Which statement about a Claisen condensation is incorrect?
Which statement about a Claisen condensation is incorrect? The reaction involves C–C bond formation. The product is a β-keto ester which resists deprotonation by the strong base in the reaction mixture. The reaction involves the condensation of two esters in the presence of strong base.
What are the three steps in the mechanism of an aldol reaction?
There are three simple steps in the mechanism of an aldol condensation: (1) get rid of the alpha hydrogen, (2) form a new carbon and carbonyl bond, and (3) convert that carbonyl group (CO) into a COH using deprotonation, which is the process of removing a proton from a molecule.
What is aldol reaction write its mechanism?
Aldol condensation is an organic reaction in which an enolate ion reacts with carboxyl compound in order to form a β– hydroxy aldehyde or β– hydroxy ketone. Hydroxide functions as a base and therefore moves the acidic a-hydrogen producing the reactive enolate ion. This reaction can be seen as an acid-base reaction.
What does aldol mean?
Definition of aldol : a colorless beta-hydroxy aldehyde C4H8O2 used especially in organic synthesis broadly : any of various similar aldehydes.
Which molecules show aldol condensation reaction?
The optimum result of cross aldol condensation reaction is possible if an aldehyde compound contains α-hydrogen and another aldehyde compound does not contain α-hydrogen. Refer to the example below to see the reaction with the mixture of ethanal and propanal.
What is the Zimmerman Traxler model of aldol reactions?
In 1957, Howard Zimmerman and Marjorie D. Traxler proposed that some aldol reactions have “six-membered transition states having a chair conformation .” This is now known as the Zimmerman–Traxler model. E -enolates give rise to anti products, whereas Z -enolates give rise to syn products.
Does lithium follow the Zimmerman Traxler model?
In reality, only some metals such as lithium reliably follow the Zimmerman–Traxler model. Thus, in some cases, the stereochemical outcome of the reaction may be unpredictable. The problem of “control” in the aldol addition is best demonstrated by an example.
How do you differentiate between Syn and anti transition states?
To differentiate two syn or two anti transition states, a chiral element must be introduced (e.g., R1, R2, or L), thereby creating diastereomeric transition states which, by definition, are of different energies. syn anti syn anti M. Movassaghi CHO R2CHO
What is the difference between enantiomeric and pericyclic transition states?
• Note: the enantiomeric transition states (not shown) are, by definition, of equal energies. The pericyclic transition state determines syn/anti selectivity.