Tpr cbt 4 bs #30

[argama]

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I got a quick question:

The question itself isn't hard: Which one of the following compounds will react most vigorously with a Grignard's?

Ok in my mind I'm like "ok most acidic one". So now I narrow down to p-nitrophenol or benzoic acid.

At this point, I don't know the Pkas of either except that they're both below 10. The answer is benzoic acid.

Is there any way to answer this WITHOUT memorizing Pka of compounds? Is there some deductive logic I was supposed to or can use? the answer explaination was "Benzoic acid is the most acidic one so that's the answer" -________-

 

[sp808]

Carboxylic acids are usually more acidic than alcohols. It's probably helpful to know generally that carboxylic acids are around 2-4 while phenols are around 10. In this case there are substituents that increase the acidity of both compounds but probably not enough to change their relative acidity. Sorry not sure if there is a better way.

 

[polyatomic]

There's a short list of pKa's you should know for the MCAT

Off the top of my head, these are the ones I always remember:

Strong acids: negatives
HF: 3ish or just know it's much weaker than strong acids
Carboxylic acids: 5 and lower
Alcohols: 15ish
Triple bonds: 26ish (or just remember it's more
Amines: 30ish

Besides that, nothing else really comes up. Also remember general properties, like conjugation and double/triple bonds increases acidity, as well as having electron-withdrawing/electronegative atoms near your acidic proton.