Organic doubt
Why is nucleophilicity a Kinetic property but basicity a thermodynamic property?
15 Replies
@Dexter
Note for OP
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Transcription requested by Opt
Because you're physically moving things around, right? Nucleophilicity means how easily a nucleophile attacks some sort of substrate. So, that has to do with physical motion. Whereas basicity or acidity, all of these are movement of electrons for the lack of a better word. Right? So, that is a stability thing. If the electron moves well, that has to do with energy. PKA and all of that. Hence, that's a thermodynamic thing.
I'm confused on this though. We always take acid-base reactions in a substrate to be faster than the corresponding electrophile-nucleophile reaction. Doesn't this mean that the basic nature of reagent is causing the kinetic product?
iteachchem
Transcription requested by Opt
You mean solvent here, not reagent?
iteachchem
Transcription requested by Opt
Because there are three things, right? One is nucleophile, one is substrate, and third is solvent.
No, I meant the reagent/nucleophile.
For example, if we have a higher amine reacting with a 1,3-dial, I learnt that de-protonation (acid-base reaction) will occur before any sort of nucleophilic attack.
One reason is orientation i presume, because acid-base reactions don't require any specific molecular orientations while nucleophilic attacks involve orbital overlap.
But other than that, isn't an acid-base reaction preferred over the nucleophilic attack ?
Ok sir
Thank you. On the acidity and basicity, what do you by it being related to movemoment of electrons?
I've studied acidity and basicity and I know their relationship with Pka and Pkb but I cannot see how it's related to movement of electron
If you mean movement of electrons kyuki H+ ko electron pair dene ka power is basicity then ham vo baat toh nucleophilicity ke liye bhi keh sakte hain-that is the ability to donate electron to atoms other than H+
Also, what do you mean by it means how easily nucleophile attacks substrate. I have the definition of both the terms and I can compare orders of both for a given set of compounds but I'm still not very clear on their definition
I also have this doubt
Just had this thought : Ham acidity basicity mein basically conjugate acid and bases ki stability ko check karte hain. So...is that what you mean by electron movement?
i.e. The acid loosing a proton to form a conjugate base
does this help?
nu: - rate of rxn
acidity/basicity: K (eq constant)
James Ashenhurst
Master Organic Chemistry
Nucleophilicity vs. Basicity
What is the difference between basicity and nucleophilicity? Basicity measures a reversible equilibrium, whereas nucleophilicity measures a rate.
this is better actually
the comments go into detail about acidity depending on multiple factors that are energy related whereas nu: is all about the rate of the reaction
so there is no 'before' when it comes to thermodynamically controlled reactions.
I am not an oc expert but if the nu: doesnt play a prominent part, it is perhaps because in the kinetics of the reaction, rate does not depend on [nu:] in that case!
same thing, yes you are right bronsted acid base theory.
lot more details given here
https://en.wikipedia.org/wiki/Thermodynamic_versus_kinetic_reaction_control
Thermodynamic versus kinetic reaction control
Thermodynamic reaction control or kinetic reaction control in a chemical reaction can decide the composition in a reaction product mixture when competing pathways lead to different products and the reaction conditions influence the selectivity or stereoselectivity. The distinction is relevant when product A forms faster than product B because th...