Advertisements
Advertisements
प्रश्न
Explain Aldol condensation of ethanal.
उत्तर
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.
1) Ethanal contains an α hydrogen atom so it undergoes the aldol condensation reaction.
2) Reaction:
- \[\ce{\underset{Ethanal}{2CH3 - CHO} ->[dil.NaOH] \underset{3-Hydroxybutanal}{CH3 - CHOH - CH2 - CHO}}\]
- \[\ce{\underset{3-Hydroxybutanal}{CH3 - CHOH - CH2 - CHO} ->[H^+] \underset{But-2-enal}{CH3 - CH = CH - CHO} + H2O}\]
3) When ethanal is treated with dilute base NaOH, KOH or sodium carbonate, two molecules of ethanal add together to form 3-Hydroxybutanal.
4) When 3-Hydroxybutanal is heated in the presence of an acid, a molecule of water is lost But-2-enal is formed.
APPEARS IN
संबंधित प्रश्न
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?
Ethanal to but-2-enal
What is meant by the following term? Give an example of the reaction in the following case.
Aldol
How will you bring about the following conversion in not more than two steps?
Ethanol to 3-Hydroxybutanal
How will you bring about the following conversion in not more than two steps?
Benzaldehyde to 3-Phenylpropan-1-ol
Complete the synthesis by giving missing starting material, reagent or product.
\[\begin{array}{cc}
\ce{C6H5CHO}\phantom{............}\\
\phantom{........}\ce{+\phantom{......}\ce{->[dil.NaOH][\Delta]}}\phantom{...}\\
\ce{CH3CH2CHO}\phantom{............}
\end{array}\]
Give reasons Acetylation of aniline reduces its activation effect.
Write chemical equations of the following reaction :
Benzoyl chloride is hydrogenated in the presence of `"Pd"/(BaSO_4)`
What is substituted imine called?
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) \[\begin{array}{cc}
\phantom{}\ce{CH3}\\
|\phantom{...}\\
\ce{CH3 - C - CHO}\phantom{..}\\
|\phantom{...}\\
\phantom{}\ce{CH3}\\
\end{array}\]
Which of the following conversions can be carried out by Clemmensen Reduction?
(i) Benzaldehyde into benzyl alcohol
(ii) Cyclohexanone into cyclohexane
(iii) Benzoyl chloride into benzaldehyde
(iv) Benzophenone into diphenyl methane
Assertion: The α-hydrogen atom in carbonyl compounds is less acidic.
Reason: The anion formed after the loss of α-hydrogen atom is resonance stabilised.
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:
\[\begin{array}{cc}
\ce{CH3}\phantom{.................}\\
|\phantom{....................}\\
\phantom{}\ce{2CH3 - C = O ->[Ba(OH)2] A ->[Δ] B + H2O}
\end{array}\]
Predict the reagent for carrying out the following transformations:
Ethanal to 3-hydroxy butanal
\[\ce{CH3-CH2-CHO ->[dil][alkali] Product}\]
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:
When acetaldehyde is treated with dilute NaOH, the following reaction is observed.
\[\begin{array}{cc}
\ce{2CH3 - CHO ->[dil.NaOH] CH3 - CH - CH2 - CHO}\\
\phantom{...............}|\\
\phantom{.................}\ce{OH}
\end{array}\]
- What are the functional groups in the product?
- Can another product be formed during the same reaction? (Deduce the answer by doing atomic audit of reactant and product).
- Is this an addition reaction or condensation reaction?
What is aldol condensation? Explain it with suitable examples.
