Acidic Hydrogen

[mario0923]

How do you determine the acidity of a hydrogen in a molecule?

for example if you have a ketone with a benzene ring in a side
H O H H
l ll l l
Ph-C-C-C-C-H
l l l
H H H

you have hydrogen on the benzene, 2 different alpha hydrogens, and a beta hydrogen
which one is the most acidic here? (by acidic I want to find the one which is easily removed right?)

or if you have an alkene within an ketone, or an alcohol group in ketone/alkene, ect...

you have different hydrogens and DAT asks questions on which hydrogen is most acidic/ have lowest pKa?

I kinda have feelings on which is more acidic but I always "guessed"

Please tell me how to determine the pKa of hydrogens.

Thanks!

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[Kahr]

How do you determine the acidity of a hydrogen in a molecule?

for example if you have a ketone with a benzene ring in a side
H O H H
l ll l l
Ph-C-C-C-C-H
l l l
H H H

you have hydrogen on the benzene, 2 different alpha hydrogens, and a beta hydrogen
which one is the most acidic here? Havıng a hard tıme decıpherıng your molecule. (by acidic I want to find the one which is easily removed right?) Rıght.

or if you have an alkene within an ketone, or an alcohol group in ketone/alkene, ect...

you have different hydrogens and DAT asks questions on which hydrogen is most acidic/ have lowest pKa? It can ask thıs, yes.

I kinda have feelings on which is more acidic but I always "guessed"

Please tell me how to determine the pKa of hydrogens. You just guestımatıng I belıeve, more acıdıc = lower pKa = more lıkely to be removed.

Thanks!

These mıght help:

http://forums.studentdoctor.net/showthread.php?t=724632

http://www.chem.ucalgary.ca/courses/350/Carey5th/useful/acidity_ladder.html

http://chemweb.unp.ac.za/chemistry/Physical_Data/pKa_values.htm

Just a note (I thınk thıs ıs rıght), the more acıdıc the H, the lower the pKa...pH and pKa both go ın the same dırectıon based on acıdıty and basıcıty. I wısh I could help you more, but ıt's been some tıme sınce I took orgo or gen chem. Hopefully someone else wıll notıce thıs post and provıde further technıcal ınput. 🙂

 

[mario0923]

These mıght help:

http://forums.studentdoctor.net/showthread.php?t=724632

http://www.chem.ucalgary.ca/courses/350/Carey5th/useful/acidity_ladder.html

http://chemweb.unp.ac.za/chemistry/Physical_Data/pKa_values.htm

Just a note (I thınk thıs ıs rıght), the more acıdıc the H, the lower the pKa...pH and pKa both go ın the same dırectıon based on acıdıty and basıcıty. I wısh I could help you more, but ıt's been some tıme sınce I took orgo or gen chem. Hopefully someone else wıll notıce thıs post and provıde further technıcal ınput. 🙂

Kahr thank you so much
I knew about the CARDIO but I do not know how to use that into comparing the acidity in a molecule.... But the 2nd link really helps me. I will just memorize that.
And the 3rd link does not work...
But Thank You So Much!!!🙂

 

[Ogoz]

In order to determine the most stable acidic H. first, you want to deprotonate an H anywhere in the structure and see if the negative charge can be stablized. the more resonance = the most stable H = the most acidic H. You would want to avoid deprotonating H from ben. ring and double/triple bonds because you dont want to detroy their stability.