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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
A compound 'A' of molecular formula C2H3OCl undergoes a series of reactions as shown below. Write the structures of A, B, C and D in the following reactions :
Write the products formed when CH3CHO reacts with the following reagents: CH3CHO in the presence of dilute NaOH
How will you bring about the following conversion in not more than two steps?
Ethanol to 3-Hydroxybutanal
Describe the following:
Cross aldol condensation
Why is alpha (α) hydrogen of carbonyl compounds acidic in nature?
Cannizaro’s reaction is not given by ______.
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) \[\begin{array}{cc}
\phantom{}\ce{CH3}\\
|\phantom{...}\\
\ce{CH3 - C - CHO}\phantom{..}\\
|\phantom{...}\\
\phantom{}\ce{CH3}\\
\end{array}\]
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?
Why are carboxylic acids more acidic than alcohols or phenols although all of them have hydrogen atom attached to a oxygen atom \[\ce{(-O-H)}\]?
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.
Give reasons to support the answer:
Presence of Alpha hydrogen in aldehydes and ketones is essential for aldol condensation.
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:
The major product of the following reaction is:
Which of the following does not give aldol condensation reaction?
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.
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:
