How to Rank Acids without a pKa Table | A Detailed Guide
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- čas přidán 27. 07. 2024
- In this video we'll discuss the 5 factors you'll use in ranking the acids according to their strength when you don't have access to the pKa table or when the pKa table is not helpful b/c you're looking at a set of molecules with the same functional group.
00:00 Types of Acid-Base Equilibria
02:52 Factor 1 - Resonance
05:48 Factor 2 - Atomic Size
07:08 Factor 3 - Electronegativity
09:03 Factor 4 - Inductive Effects
12:08 Factor 5 - Hybridization
13:51 Recap
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Such an effective lesson in less that 20 min.! 😂 Brilliant work!
Haha, thank you, Curt! I try to prioritize the "how-to" aspects in my tutorials rather than a list of boring facts. I mean, at the end of the day, you're not going to be tested on facts in organic chemistry but on your ability to solve the problems.
May I ask if the factors are arranged in order of importance? i.e., does resonance take precedence over atomic size, atomic size over electronegativity, and so on? Thank you so much for the video; it was very informative and well-explained.
Roughly. The only trend that will always be true is the size always beats electronegativity. Everything else is a general guideline and may change depending on the molecule. pKa table is always going to be your best friend.
ok got it!! thank you for the quick response 🙏🏼 @@VictortheOrganicChemistryTutor
Hello, in your example of Inductive effect, What if instead of fluorine it was oxygen? from my understanding oxygen is an EDG so would it destabilize the charge?
It's a pretty common misconception. Oxygen has a strong negative inductive effect (pulls electrons) and equally strong positive resonance effect (can give electrons via resonance). If both effects are in play, then the resonance effect typically overpowers. If only inductive effect is at play, in other words, there's no resonance, then it's a strong electron withdrawing group.
@@VictortheOrganicChemistryTutor Thank you for the very fast reply, that makes a lot of sense, thanks again!
@@VictortheOrganicChemistryTutor I have another question which I have been struggling with for a few days now, and I am failing to understand. I am hoping you may help me if possible.
So the ARIO concept is simply a pneumonic device meant to help memorize the four key factors that affect acidity, there is no order in which one will overpower another, correct?
for example Alkynes are more acidic then Amines despite Amines having a more Electronegative atom.
If this is the case, how can I tell which molecule is more acidic then the other if I have one molecule effected by 2 inductive forces and one molecule by one resonance?
Thank you again, Its my first year in Ochem so I apologize if it is simply me not understanding a more basic concept.
*mnemonic device 😉
ARIO model, popularized by David Klein in his "Organic Chemistry as a Second Language," is limited by its simplicity. The only way to truly explain the trends would be if we delve into the molecular orbital interactions and intricacies of equilibrium which go beyond the scope of an introductory sophomore organic chemistry. So, we limit ourselves to these simplified models. None of which work well. The pKa table is your best friend here. Typically, you won't see questions where you need to compare things that are too complex to analyze. You'll "grow a nose" for those trends with some practice.
@@VictortheOrganicChemistryTutor thank you again! :)