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Topic: I effect Problem  (Read 3412 times)

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Offline ritwik06

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I effect Problem
« on: January 12, 2010, 10:50:45 AM »
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.

 

Offline aieeee

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Re: I effect Problem
« Reply #1 on: January 12, 2010, 12:02:13 PM »
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 ).

Offline Schrödinger

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Re: I effect Problem
« Reply #2 on: January 12, 2010, 12:48:21 PM »
@aieeee : So do you mean to say that NR3 is less basic than ammonia?

(R=alkyl group)
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Offline aieeee

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Re: I effect Problem
« Reply #3 on: January 12, 2010, 01:40:40 PM »
dude,see , these ions , I'm mentioning can be formed in aqueous solution. thus take water as the medium and think about it again.

Offline orgopete

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Re: I effect Problem
« Reply #4 on: January 12, 2010, 07:01:40 PM »
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.
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Offline ritwik06

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Re: I effect Problem
« Reply #5 on: January 12, 2010, 11:05:53 PM »
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?

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