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प्रश्न
Explain Aldol condensation of ethanal.
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उत्तर १
Aldehydes containing at least one α –hydrogen atom undergo a reaction in the presence of dilute alkali (dilute NaOH, KOH or Na2CO3) as a catalyst to form β-hydroxy aldehydes (aldol). This reaction is known as the aldol reaction.
Ethanal contains an α-hydrogen atom, so it undergoes the aldol condensation reaction.
\[\ce{\underset{Ethanal}{2CH3 - CHO} ->[dil{.} NaOH] \underset{3-Hydroxybutanal}{CH3 - CHOH - CH2 - CHO}}\]
\[\ce{\underset{3-Hydroxybutanal}{CH3 - CHOH - CH2 - CHO} ->[H+] \underset{But-2-enal}{CH3 - CH = CH - CHO} + H2O}\]
When ethanal is treated with dilute base NaOH, KOH or sodium carbonate, two molecules of ethanal add together to form 3-Hydroxybutanal. When 3-Hydroxybutanal is heated in the presence of an acid, a molecule of water is lost, and But-2-enal is formed.
उत्तर २
The carbon atom adjacent to the carbonyl carbon atom is called the α-carbon atom (α − C).
\[\begin{array}{cc}
\phantom{.........}\ce{O}\\
\phantom{.........}||\\
\ce{- \overset{\beta}{C} - \overset{\alpha}{C} - C - \overset{\alpha}{C} -}\\
|\phantom{.....}\\
\ce{H^\alpha}\phantom{...}\\
\end{array}\]
Aldol condensation reaction is a characteristic reaction of aldehydes and ketones containing an active α-hydrogen atom.
When aldehydes or ketones having α-H atoms are heated with a dilute base or dilute acid, two molecules undergo self-condensation to yield β-hydroxy aldehyde (aldol) or β-hydroxy ketone (ketol), respectively. The reaction is referred to as the aldol addition reaction.
For aldehyde:
Acetaldol, on heating, undergoes subsequent elimination of water, giving rise to α, β-unsaturated aldehyde.
The overall reaction is called aldol condensation. It is a nucleophilic addition-elimination reaction.
संबंधित प्रश्न
Write the products formed when CH3CHO reacts with the following reagents: CH3CHO in the presence of dilute NaOH
How will you convert ethanal into the following compound?
But-2-enal
How will you bring about the following conversion in not more than two steps?
Benzaldehyde to 3-Phenylpropan-1-ol
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Cross aldol condensation
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\[\begin{array}{cc}
\ce{C6H5CHO}\phantom{............}\\
\phantom{........}\ce{+\phantom{......}\ce{->[dil.NaOH][\Delta]}}\phantom{...}\\
\ce{CH3CH2CHO}\phantom{............}
\end{array}\]
Why is alpha (α) hydrogen of carbonyl compounds acidic in nature?
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Propanone is treated with dilute Ba (OH)2-.
Write chemical equations of the following reaction :
Benzoyl chloride is hydrogenated in the presence of `"Pd"/(BaSO_4)`
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Explain aldol condensation reaction in detail.
Which product is formed when the compound 
is treated with concentrated aqueous \[\ce{KOH}\] solution?
Compounds A and C in the following reaction are:
\[\ce{CH3CHO ->[(i) CH3MgBr][(ii) H2O] (A) ->[H2SO4, Δ] (B) ->[Hydroboration oxidation] (C)}\]
Which of the following compounds do not undergo aldol condensation?
(i) \[\ce{CH3 - CHO}\]
(ii) 
(iii) \[\begin{array}{cc}
\phantom{}\ce{O}\\
\phantom{}||\\
\ce{CH3 - C - CH3}
\end{array}\]
(iv) \[\begin{array}{cc}
\phantom{}\ce{CH3}\\
|\phantom{...}\\
\ce{CH3 - C - CHO}\phantom{..}\\
|\phantom{...}\\
\phantom{}\ce{CH3}\\
\end{array}\]
What product will be formed on reaction of propanal with 2-methylpropanal in the presence of \[\ce{NaOH}\]? What products will be formed? Write the name of the reaction also.
Compound ‘A’ was prepared by oxidation of compound ‘B’ with alkaline \[\ce{KMnO4}\]. Compound ‘A’ on reduction with lithium aluminium hydride gets converted back to compound ‘B’. When compound ‘A’ is heated with compound B in the presence of \[\ce{H2SO4}\] it produces fruity smell of compound C to which family the compounds ‘A’, ‘B’ and ‘C’ belong to?
When liquid ‘A’ is treated with a freshly prepared ammoniacal silver nitrate solution, it gives bright silver mirror. The liquid forms a white crystalline solid on treatment with sodium hydrogensulphite. Liquid ‘B’ also forms a white crystalline solid with sodium hydrogensulphite but it does not give test with ammoniacal silver nitrate. Which of the two liquids is aldehyde? Write the chemical equations of these reactions also.
Identify A and B from the following reaction:
\[\begin{array}{cc}
\ce{CH3}\phantom{.................}\\
|\phantom{....................}\\
\phantom{}\ce{2CH3 - C = O ->[Ba(OH)2] A ->[Δ] B + H2O}
\end{array}\]
\[\ce{CH3-CH2-CHO ->[dil][alkali] Product}\]
The product in the above reaction is:
Which of the following compounds will undergo self-condensation in the presence of dilute NaOH solution?
Assertion (A): The final product in Aldol condensation is always α, β-unsaturated carbonyl compound.
Reason (R): α, β-unsaturated carbonyl compounds are stabilised due to conjugation.
Identify A and B:
What is aldol condensation? Explain it with suitable examples.
Which one of the following undergoes reaction with 50% sodiumhydroxide solution to give the corresponding alcohol and acid:
