[ritwik06]

Why does NR₃⁺ have greater -I effect than NH₃⁺ ?
I think otherwise because alkyl groups have a  +I effect which would enhance electron density on N centre.

 

[aieeee]

actually , this happens due to steric hindrance caused by the bulky alkyl groups surrounding NR₃⁺.thus , its not easy to donate electrons in such a state. thus NR₃⁺ shows -I effect much more than NH₃⁺
(NH₃⁺ doesn't hv bulkier groups surrounding ).

[Schrödinger]

@aieeee : So do you mean to say that NR₃ is less basic than ammonia?

(R=alkyl group)

[aieeee]

dude,see , these ions , I'm mentioning can be formed in aqueous solution. thus take water as the medium and think about it again.

[orgopete]

I am going to take a guess at this. This is the opposite of what I expected. As I recall, the parameters for +/-I, etc. are derived empirically. So, if a reaction were performed, a nitration of trimethylanilinium and anilinium chloride for example, the trimethylanilinium chloride would have a greater amount of meta substitution and the reaction rate slower.

I suspect that while the electrophilic substitution reaction (or other reactions in which the -I effect is being measured) is essentially a kinetic process, anilinium ion can also participate in a deprotonation reaction as well. Although this is a thermodynamic process in which the anilinium ion is favored, aniline itself will have a +I value and can incrementally increase the apparent -I value.

I am not inviting anyone to believe this. I am only making a guess. If more data were presented, my guess could be more easily verified, refuted, or another explanation suggested.

[ritwik06]

actually , this happens due to steric hindrance caused by the bulky alkyl groups surrounding NR₃⁺.thus , its not easy to donate electrons in such a state. thus NR₃⁺ shows -I effect much more than NH₃⁺
(NH₃⁺ doesn't hv bulkier groups surrounding ).

@aieeee : So do you mean to say that NR₃ is less basic than ammonia?

(R=alkyl group)

I am going to take a guess at this. This is the opposite of what I expected. As I recall, the parameters for +/-I, etc. are derived empirically. So, if a reaction were performed, a nitration of trimethylanilinium and anilinium chloride for example, the trimethylanilinium chloride would have a greater amount of meta substitution and the reaction rate slower.

I suspect that while the electrophilic substitution reaction (or other reactions in which the -I effect is being measured) is essentially a kinetic process, anilinium ion can also participate in a deprotonation reaction as well. Although this is a thermodynamic process in which the anilinium ion is favored, aniline itself will have a +I value and can incrementally increase the apparent -I value.

I am not inviting anyone to believe this. I am only making a guess. If more data were presented, my guess could be more easily verified, refuted, or another explanation suggested.

I got this. Here is my view on this. In water or any polar medium, the alkyl bulky groups dont allow water or polar molecules to stabilise formal positive charge on nitrogen. Thats why it has a greater electron pulling tendency.
But the point mentioned by orgopete is worth noting, Why would meta substitution be favored more on trimethylanilinium than anilinium chloride?
@ By the way, is the solvent polar in this nitration reaction?