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प्रश्न
What is meant by the following term? Give an example of the reaction in the following case.
Aldol
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उत्तर
Aldehydes and ketones having at least one α-hydrogen undergo a reaction in the presence of dilute alkali as catalyst to form β-hydroxy aldehydes (aldol) or β-hydroxy ketones (ketol), respectively. This is known as the aldol reaction.
\[\begin{array}{cc}
\ce{\underset{Ethanal}{2CH3-CHO}<=>[dil.NaOH] CH3 - CH - CH2 - CHO ->[\Delta][-H2O]\underset{But-2-enal}{CH3 - CH = CH - CHO}}\\
|\phantom{.....................}\\
\ce{\underset{(Aldol)}{\underset{3-Hydroxybutanal}{OH}}}\phantom{...................}\
\end{array}\]
\[\begin{array}{cc}
\phantom{..................}\ce{CH3}\phantom{.............................}\ce{CH3}\\
\phantom{..............}|\phantom{.................................}|\\
\ce{\underset{Propanone}{2CH3 - CO - CH3} <=>[Ba(OH)2] CH3 - C - CH2CO - CH3->[\Delta][-H2O]\underset{(Aldol condensation product)}{\underset{4-Methylpent-3-en-2-one}{CH3 - C = CH - CO - CH3}}}\\
|\phantom{...................}\\
\ce{\underset{4-Hydroxy-4-methylpentan-2-one}{\underset{(Ketol)}{OH}}}\phantom{................}\
\end{array}\]
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संबंधित प्रश्न
Which of the following compounds would undergo aldol condensation, which the Cannizzaro reaction and which neither? Write the structures of the expected products of aldol condensation and Cannizzaro reaction.
- Methanal
- 2-Methylpentanal
- Benzaldehyde
- Benzophenone
- Cyclohexanone
- 1-Phenylpropanone
- Phenylacetaldehyde
- Butan-1-ol
- 2, 2-Dimethylbutanal
Describe the following:
Cross aldol condensation
Why is alpha (α) hydrogen of carbonyl compounds acidic in nature?
Write chemical equations of the following reaction :
Benzoyl chloride is hydrogenated in the presence of `"Pd"/(BaSO_4)`
Write a chemical equation for the following reaction:
Propanone is treated with dilute Ba( OH)2.
Why is there a large difference in the boiling points of butanal and butan-1-ol?
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?
Assertion: Aromatic aldehydes and formaldehyde undergo Cannizaro reaction.
Reason: Aromatic aldehydes are almost as reactive as formaldehyde.
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.
Which of the following gives aldol con~ensation reaction?
Predict the reagent for carrying out the following transformations:
Ethanal to 3-hydroxy butanal
Explain the aldol condensation of ethanal.
Which of the following does not give aldol condensation reaction?
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.
Write a note on the aldol condensation reaction of acetaldehyde.
