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Priya Gorakshnath Anandkar Grade: 12
           R      RELATIVE BASIC STENGTH FOR AMINES 

CH3 SEC> PRI.> TER >NH3
C2H5 SEC> TER> PRI> NH3
(CH3)2CH PRI> NH3> SEC >TER
(CH3)3C NH3 >PRI>SEC>TER
WHY THIS IS SO PLZ EXPLAIN ? THANKS FOR REPLY !!!!!!!
6 years ago

Answers : (1)

SAGAR SINGH - IIT DELHI
879 Points
										

Dear student,


basicity order of amines

The basic strength in aqueous solution depends not only upon electron releasing effect but also upon steric effect and hydration effect.


a) Steric effect


Steric effect refers to the crowding of alkyl groups around N atom which hinders the attack of proton on the amine molecule and this decreases its basic strength. Since crowding of alkyl groups around N atom increases from 1o to 3o amines, the basic strength of amine should decrease in the order 1o > 2o > 3o.


b) Hydration effect


Hydration effect refers to the stabilization of the protonated amine by water molecules. The water molecules from H - bonds with the protonated amine and release energy called hydration energy.


Greater the extent of H - bonding in protonated amine more will be its stabilization and consequently greater will be the basic strength of the corresponding amine.


Hydration due to hydrogen-bonding is maximum in monoalkyl ammonium ion (protonated cation of 1o amine), it is less in dialkyl ammonia ion and still less in trialkyl ammonium ion. Thus basic strength should decrease from 1o > 2o > 3o.


In 3o amine, hydration is least, steric hinderance is maximum so least basic inspite of maximum inductive effect.


In 1o amine, steric hinderance is least, hydration is maximum and inductive effect is minimum. So its basic strength is more than 3o amine.


The resultant of all factors cause 2o amine to be still more basic than 1o amine.


So overall basic strength varies as 2o > 1o > 3o.



 


















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Please feel free to ask your queries here. We are all IITians and here to help you in your IIT JEE preparation.


All the best.


Win exciting gifts by answering the questions on Discussion Forum. So help discuss any query on askiitians forum and become an Elite Expert League askiitian.


Now you score 5+15 POINTS by uploading your Pic and Downloading the Askiitians Toolbar  respectively : Click here to download the toolbar..


 


Askiitians Expert


Sagar Singh


B.Tech, IIT Delhi


















6 years ago
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