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Give reason for the following: (i) Aldehydes are more reactive than ketones towards nucleophilic reactions. (ii) pK a value of acetic acid is higher than pK a value of chloroacetic acid.

Give reason for the following: (i) Aldehydes are more reactive than ketones towards nucleophilic reactions. (ii) pK a value of acetic acid is higher than pK a value of chloroacetic acid.

Grade:upto college level

1 Answers

Gaurav
askIITians Faculty 164 Points
9 years ago
Hello Student
i. Aldehydesare usuallymore reactive toward nucleophilicsubstitutionsthan ketonesbecause of both steric and electronic effects. Because of steric hinderence, the nucleophile feels it more difficult to attach the carbonyl carbon atom of ketone.

ii.pkaof acetic acid is 4.23 and chloroacetic acid is 2.3.
pka value depends upon the strength of acid. The stronger acid will have lesser pKa value and weaker acid will have higher pKa value.The value indicates that chloroacetic acid is stronger acid than acetic acid.
This can be explained on the basis of inductive effect of Cl.Cl being highly electronegative will pull the electrons towards itself This will polarize the C-Cl bond and in turn also polarize the C-O and O-H bonds.Due to this there would be easy removal of H+ ion. Moreover anion formed by removal of H+ will also stabilized by electron pulling nature of Cl.

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