Which is more acidic?

[Tina324]

HOOCCH2COOH is the alpha hydrogen the most acidic?

also which is more acidic..H2S or PH3 and why?

Merci =)

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[DDS13]

HOOCCH2COOH is the alpha hydrogen the most acidic?

also which is more acidic..H2S or PH3 and why?

Merci =)

its seems like, im getting everything wrong, well, ill give it a shot, i think hydroxyl hydrogen is more acidic than the alpha in this case because it is directly bonded to an O.

i think H2S is more acidic, since S is more eneg and heavier than P. what is the right answer?

 

[Tina324]

its seems like, im getting everything wrong, well, ill give it a shot, i think hydroxyl hydrogen is more acidic than the alpha in this case because it is directly bonded to an O.

i think H2S is more acidic, since S is more eneg and heavier than P. what is the right answer?

the first one i made up..so i dunno lol
the second one, PH3 is more acidic. i THINK its because S has two lone pairs, so it acts like a base...also when removing an H from P..P is bigger, so it can spread the charge around more..but ur right S is more electronegative...arggg

SOMEONE...HELP...i need like flat out rules for comparing acidicty. what overides what? electronegativity..size of atom...what? lol

 

[utdent20]

I am not sure but I believe electronegativity rides over the size of the atom

 

[tranv117]

I am not sure but I believe electronegativity rides over the size of the atom

I think its the other way around. Easy example would be to compare HI and HF. HI is more acidic then HF although F is more electronegative then I. Since I is a bigger atom, it's bond with H is longer and weaker. H-I can give up that proton much easier than H-F so HI is more acidic.

 

[pidbull]

first question is really good, anyone know for sure?

2nd one I agree with tranv

 

[Sea of ASH]

i just finished reviewing this... the alpha hydrogen located between two carboxyl groups is pretty acidic (pKa~10). this is becuz once it leaves it produced a carbanion that is stabilize by the electron withdrawing effect of the two carbonxyl groups

for the second on i dont think it has anything to do with lone pairs, IMO its more related to EN. therefore i believe that H2S is more acidic.

correct me if im wrong but HF forms H-bonds so its hella stable and doesnt want to dissassociate and HI would be more acidic.... this is just an expection

 

[tranv117]

i just finished reviewing this... the alpha hydrogen located between two carboxyl groups is pretty acidic (pKa~10). this is becuz once it leaves it produced a carbanion that is stabilize by the electron withdrawing effect of the two carbonxyl groups

for the second on i dont think it has anything to do with lone pairs, IMO its more related to EN. therefore i believe that H2S is more acidic.

correct me if im wrong but HF forms H-bonds so its hella stable and doesnt want to dissassociate and HI would be more acidic.... this is just an expection

I would have to disagree and say the H in OH of the carboxylic acid is more acidic then the alpha Hs

 

[211183]

I would have to disagree and say the H in OH of the carboxylic acid is more acidic then the alpha Hs

I believe Sea of Ash is right.
The alpha carbon is most acidic in the middle because it creates resonance with the two double bonded O....

What is the reagent that removes the acidic proton in order for alkylation to occur??

 

[tranv117]

hmmm, imma have to restudy this cause its confusing me now...😳

But i get what you're talking about.

 

[Sea of ASH]

when the carboxylic H's, the compound becomes less stable than when the alpha H leaves:

 

[tranv117]

when the carboxylic H's, the compound becomes less stable than when the alpha H leaves:

thanks

 

[Sea of ASH]

no prob tranv

plus another way to look at it is that the H's on the carboxyl group is H-bonding so it is very "comfortable" in that form and does not want to leave as much as the alpha carbon....

 

[211183]

anyone remember what reagant removes that H+???

 

[anesthesia_209]

I would guess that the carboxylic hydrogen is the most acidic due to the O being more electronegative (a lot more stable with the negative charge). Plus add on the fact that the negative charge will resonate between the two oxygen atoms either way (whether you deprotonate the alpha carbon or on the carboxylic hydrogen).

H2S is more acidic because, given that you're in the same period, size barely changes and therefore, electronegativity rules. If you were to jump down a row, the increase in size would be the deciding factor.

 

[anesthesia_209]

anyone remember what reagant removes that H+???

Any weakly/non-neucleophilic base should do.

 

[Tina324]

oops i made a mistake..yes H2S is more acidic.

ok, what is the reason now? becuase H is bigger than P, so it can stabilize the charge that the S leaves behind?

 

[Tina324]

o and that it's electronegative?

 

[Tina324]

oooops..again, damn i must be tired...because S is surely NOT bigger than P...ok so th eonly reason why H2S is more acidic is because S is more electronegative ? THerefore electronegativity overides size?

 

[keliao]

so what if you compare between O and P, which one is more acidic?
acidity increases from left to right, top to bottom.

 

[anesthesia_209]

so what if you compare between O and P, which one is more acidic?
acidity increases from left to right, top to bottom.

P should be more acidic.

If you stay in the same row, go by electronegativity.

If you go up or down a row, go by size.

 

[keliao]

true that...thanks

 

[Sea of ASH]

Plus add on the fact that the negative charge will resonate between the two oxygen atoms either way (whether you deprotonate the alpha carbon or on the carboxylic hydrogen).

it will resonate between the two oxygens on one carbon but in the attachment you will see that it resonates on the two oxygens that are attached to two different carbons. and the charge has an additional spot to go to, the alpha carbon. so thats 3 different spots it can go total while delocalizing. in ur argument you got 2 spots with less delocalization

 

[anesthesia_209]

it will resonate between the two oxygens on one carbon but in the attachment you will see that it resonates on the two oxygens that are attached to two different carbons. and the charge has an additional spot to go to, the alpha carbon. so thats 3 different spots it can go total while delocalizing. in ur argument you got 2 spots with less delocalization

True but resonance also depends on the type of atoms that the charge is shared with. On top of that, resonance isn't the only reason why the carboxylic O would be more acidic. Electronegativity also comes into play.

pKa of the alpha hydrogens of diketons usually run a little over 10. While carboxylics are ~5. In a basic condition, where you would deprotonate the alpha carbon, you would also deprotonate the carboxylic oxygens. This would result in competition for the carbonyls. So, I would guess that malonic acid's alpha-hydrogen pKa is even higher.

 

[tranv117]

so after doing a little research on this. The carboxylic acid H is definately more acidic than the alpha protons.

pka of alpha protons are typically in the range of 17-19 while carb acid pka is about 3-5

 

[klutzy1987]

Im not sifting through all of these posts, but without question the Carboxy acid is much much much more acidic than the alpha hydrogen. One is an acid one is just more stable carbocation. Acid is alwasys more acidic than a non acid.

 

[achilles2]

HOOCCH2COOH is the alpha hydrogen the most acidic?

also which is more acidic..H2S or PH3 and why?

Merci =)

I'd put the ester side hydroxyl hydrogen...but thats just me

HOOCH1COOH

Its got two oxygen (highly electronegative pulling away density