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(A) p-methoxy benzaldehyde is less recat...

(A) p-methoxy benzaldehyde is less recative than bensaldehyde towards cyanohydrin formation.
(R) The +R effect methoxy group increases the electron deficiency of the carbonyl carbon.

A

If both (A) and (R) are correct and (R) is the corect explanation of (A)

B

If both (A) and (R) are correct but (R) is not correct explanation of (A)

C

If (A) is correct but (R) is incorrect.

D

If (A) is incorrect but (R) is correct

Text Solution

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The correct Answer is:
C
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Assertion: Phenol is more reactive than benzene towards electrophilic reactions. Reason : The +R effect of OH group increases the electron density on benzene nucleus.

Assertion: Benzaldehyde is more reactive than ethanal towards nucleophilic attact. Reason : The overall effect of- l and +R effect of phenyl group decrease the electron density on the carbon atom of gtC = O group in benzaldehyde.

(A) Benzaldehyde is less reactive than acetaldehyde towards nucleophiles. ltBRgt (R) Carbonyl carbon in benzaldehyde has less positive charge than that of carbonyl carbon in acetaldehyde due to resonance.

Aldehydes and ketones ar specially susecptible to nucleophilic addition because carbonyl group is polar (due to electronegativity difference between carbon and oxygen) Positive charge on carbon makes it reactive towards the nucleophili. This addition is catalysed by acid. Reactivity of carbonyl compound towards nucleophilic addition increases with increases in the electron deficiency at carbonyl carbon. Thus, (-I.E.)groups increase while (+I.E.) groups decrease the reactivity of carbonyl compound. Select the least reactive carbonyl compound for nucleophilic addition :

Aldehydes and ketones ar specially susecptible to nucleophilic addition because carbonyl group is polar (due to electronegativity difference between carbon and oxygen) Positive charge on carbon makes it reactive towards the nucleophili. This addition is catalysed by acid. Reactivity of carbonyl compound towards nucleophilic addition increases with increases in the electron deficiency at carbonyl carbon. Thus, (-I.E.)groups increase while (+I.E.) groups decrease the reactivity of carbonyl compound. Which among the following is most reactive to give nucleophilic addtion ?

OP TANDON-ALDEHYDES AND KETONES -ASSERTION-REASON TYPE QUESTIONS
  1. (A) Carbonyl compounds take part in nucleophilic addition reactions. ...

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  2. (A) Primary alcohols can be easily oxidised to aldehydes. (R) Aldehy...

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  3. Assertion: The addition of ammonia derivative to a carbonyl compound i...

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  4. (A) Fehiling's reagent is a test for all aliphatic aldehydes. (R) Al...

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  5. (A) 2-Methlpropanal undergoes Cannizzaro's reaction. (R) It has no a...

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  6. Assertion (A) Formaldehyde is a planar molecule. Reason (R) It conta...

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  7. (A) Nitromethane can give aldol condensation. (R) alpha hydrogen of ...

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  8. Assertion : Chloral hydrate is a stable compound. Reason : It is sta...

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  9. (A) Acetaldehyde does not show aldol condensation. (R) Compounds ha...

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  10. (A) Lower aldehydes and ketones are soluble in water but solubility de...

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  11. Assertion : Dimethyl sulphide is commonly used for the reduction of a...

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  12. (A) alpha-hydrogen atom of carbonly compouns is acidic in nature. (R...

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  13. Assertion (A): The following intramolecular aldol reaction occurs. ...

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  14. (A) Acetaldehyde reduces Fehlintgs' solution but benzaldehyde does not...

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  15. (A) p-methoxy benzaldehyde is less recative than bensaldehyde towards ...

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  16. (A) Benzaldehyde gives a positive test with Benedict's and Fehiling so...

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