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Werewolf

In solution phase we know that secondary amines are the most basic .....

What comes next? Primary or tertiary ?

Werewolf

Reply

sandeepramesh

I should think primary because of the extensive H bonding

computer001

but alkyl grps being more +i will inc the free elec on N no??
so tht also shud be take into consideration??

computer001

if i rem rite its supposed to be :
if alkyl size>ch3
then it will be s>p>t
for che i is s>t>p

Werewolf

Ok I have read both these orders in different books 2>1>3 and 2>3>1

Now I need majority .

Werewolf

ashgirl

2>1>3> NH3

actually, the order shud be 3>2>1>NH3 coz more the number of alkyl groups, more is the electron density on N.

but in aq soln, the basicity depends upon +I effect, H-bonding, streic effects

due to +I effect, 3>2>1 is correct order

due to hbonding, 1>2>3

due to steric effect, 2>3>1

so, in short ---->

2>1>3>NH3

Werewolf

Quote by ashgirl : due to steric effect, 2>3>1

Please explain it .

ashgirl

this is in the case when the alkyl group is bigger than CH3 group.

due to the presence of large grps there will be steric hinderance and hence 3' amines will be less basic than 2' but bcoz of greater +I effect in 3' than in 1',

3' will be more basic than 1'....

hope u got it!!

sorry one more point to add-----

"steric hinderance to H bonding"

Werewolf

But you have already considered +I effect separately

you wrote

due to +I effect, 3>2>1 is correct order

due to hbonding, 1>2>3

due to steric effect, 2>3>1

this means that the third sequence is only due to steric and +I is not involved in it as u have already taken +I in the first series so the third series should be 1>2>3 ? because 1 has least steric crowding and 3 the most.

dream

hey werewolf,
the answer lies in both inductive effect as well as steric hindrance

due to inductive effect the expected order is 3>2>1

but due to steric hindrance in tert-amines, they are weaker bases

hence the order of basic strength of amines is 2>1>3>NH3

lalitvijay17

in gaseous phase 3⁰>2⁰>1⁰.. (basicity)

in aqueous medium for meyhyl amine -2⁰>1⁰>3⁰.
for ethyl amine 2⁰>3⁰>1⁰

tarinbansal

Ya, the answer is 2>1>3>NH3.

But it has nothing to do with steric hindrance.

It is found by collective result of both +I effect and HYDRATION effect.
It is found by the stability of conjugate acid.
More the neutralisation of +ve charge, more will the stability of C.A and more will be the basicity.
Now more the +I effect, more the neutralisation.
Also MORE THE HYDRATION, MORE THE NEUTRALISATION.

Hydration is difficult in compounds with bulkier groups. So it will be least in tertiary but we cant neglect the very high +I effect in it.

So the ans comes out to be- 2>1>3>NH3

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