Talk:Carboxylic acid

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Dissociation fraction[edit]

"For example, at room temperature, only 0.4% of all acetic acid molecules are dissociated. Electronegative substituents give stronger acids."

I'm not a chemist, but the above sentence confused me greatly. At pH 7, nearly *all* acetic acid molecules are dissociated, right?

I imagine that this might refer to a 1.0 M solution (which has a pH of 2.4), as stated in the Acetic Acid page:
A 1.0 M solution (about the concentration of domestic vinegar) has a pH of 2.4, indicating that merely 0.4% of the acetic acid molecules are dissociated.  — Preceding unsigned comment added by 5.179.82.4 (talk) 09:10, 24 May 2013 (UTC) 


Untitled[edit]

what is sodium benzoates lewis structure?

Why are you asking something like that on here? This isn't a help page. I don't mean to be rude, but there are better places to post questions like that.

Regarding the flag on the main page. Unless you are planning on having a section on carboxylic acid derivatives (which is not a bad idea), I don't think merging the carbonyl article with this one is a good idea. What about aldehydes, esters, ketones, etc.? Dawhitfield 00:24, 7 August 2005 (UTC)

I think it's about merging with carboxyl, not carbonyl.

There should probably be a section about protecting acids as esters. —Preceding unsigned comment added by 68.10.7.182 (talk) 07:43, 31 March 2008 (UTC)

Common Names[edit]

Why does this page focus on 'Common Names' (as they are referred to) rather than IUPAC names? Is Ethanoic acid not more common than Acetic acid now-a-days? Are IUPAC names not the official names now? Jklsc (talk) 11:13, 7 May 2011 (UTC)

No, IUPAC names are uncommon for many if not most acids. The consensus in Wikipedia-Chemistry does not to follow IUPAC when a common name is more prevalent. Lots of new editors (especially ones that contribute almost zero chemical content), are rather adamant about nomenclature, but they eventually desist.--Smokefoot (talk) 12:38, 7 May 2011 (UTC)

Carbonic acid?[edit]

Is carbonic acid (HOCOOH) a carboxylic acid? --Damian Yerrick () 02:38, 15 December 2006 (UTC)

Generally no. It is usually considered an inorganic acid. Also, it easily decomposes to CO2 and water. —Preceding unsigned comment added by 68.10.7.182 (talk) 07:40, 31 March 2008 (UTC)

The simple answer is "yes"... HO-COOH --FK1954 (talk) 17:21, 12 March 2010 (UTC)

Polarity[edit]

The article says: "Carboxylic acids are polar", and I can understand why, but why is it on certain molecules, adding a carboxylic acid reduces the hydrophilicity / increases the lipophilicity, e.g:

Serotonin-skeletal.png 5-hydroxytryptophan.png

5-hydroxy-tryptamine is fairly polar and can't cross the BBB, and 5-hydroxy-α-carboxyl-tryptamine (5-OH-tryptophan) is fairly non-polar and can cross the BBB.

What is the cause of this? --Mark PEA 19:48, 26 March 2007 (UTC)

It has to do with the presence of both basic and acidic groups within the same molecule. These types of compounds can exist as zwitterions. At some pH, the isoelectric point, the molecules have no net charge and their water solubility decreases (they show more lipophilicity). I hope this helped. Silverchemist (talk) 05:25, 1 April 2008 (UTC)
No, 5-HTP (5-hydroxytryptophan) is extremely polar and cannot cross a lipid barrier. It has actually the highest polarity at the isoelectric point. 5-HTP can cross the blood brain barrier only because there are specialized transporter proteins for it. Сасусlе 06:07, 1 April 2008 (UTC)

Proton bouncing[edit]

Pardon my ignorance, but is the proton of a carboxyl group fixed to one oxygen, or can it jump between the two? Presumably in water solution the H+ can leave one oxygen and reattach to the other; but what about in water-free environments (pure solid, liquid or gas)? In the dimeric form, can the two hydrogens simultaneously jump across the hydrogen bonds and bond to the facing oxygen, while the C=O bonds swap with the C-O bonds? What are the energy barriers for these swaps? All the best, --Jorge Stolfi (talk) 14:02, 17 November 2009 (UTC)

Yes protons do hop in these compounds. The process is degenerate (equal energy, which for organic cmpds often implies that the process is also fast). I dont know much about the details, but the usual picture is that proton hopping occurs via dimers that have an eight-membered C2O4H2 ring, as shown in the 4th picture down on the right in the article. The structure of solid or gaseous carboxylic acids often reveal such 8-membered rings. In the presence of water or related H-bond donors, proton hopping probably occurs via intervening solvent. The inorganic carbon things that interest you often have low solubility because of the presence of extended H-bonding networks. You have touched on a huge topic.--Smokefoot (talk) 15:03, 17 November 2009 (UTC)
Could you perchance recommend a reference on this topic? Thanks... --Jorge Stolfi (talk) 23:21, 19 February 2010 (UTC)

0.02% deprotonated acetic acid?[edit]

I don't know where anyone got this number. From the pKa, it seems that at pH 7 nearly all of it is deprotonated. At [A-]=[H+] I get 0.4% deprotonation. This website http://www.molecularsoft.com/help/acid_and_base-weak_acid_base_dissociation.htm also comes up with the value 0.4%. Am I doing something wrong? Its 0.02% at pH 0 but thats hardly reasonable. —Preceding unsigned comment added by 128.6.22.134 (talk) 17:18, 23 March 2011 (UTC)

For weak acids like acetic acid, the proportion of the acid that's dissociated is a function of the concentration. At one extreme, you can imagine pure acetic acid, in which none of the molecules will be deprotonated (that's not true, really, because it has its own K_autodissociation of 3.5 x 10-15 M, and since the molarity of pure acetic acid is 17M, 3.5e-15/17 = 0.00000000000002% dissociated). And at the other extreme, a single molecule of acetic acid in a large volume (say, a liter) of water, the acetic acid will be 100% deprotonated because the one molecule won't change the pH until the 25th decimal place, and so with a pKa of 4.75, the probability of not being dissociated for that one molecule is less than 1%. --Atemperman (talk) 03:53, 7 August 2013 (UTC)

Carboxyl groups definition missing[edit]

This page is a redirect from Carboxyl group. However, an explicit definition of carboxyl group is not provided. I don't have a chemistry background, but I'd led to assume that the carboxyl is the carbon double bonded to an oxygen atom and singly bonded to a hydoxyl group. If someone iwth more expertise than me could update the page I an other users would appreciate it. 68.194.106.90 (talk) 16:56, 10 April 2011 (UTC)Comma Service

The lede needs help![edit]

It reads like an upper-level textbook instead of a few-sentence summary accessible to educated laymen. It's fair to expect Wikipedia readers to have some education, but remember that nearly all are laymen. I'd fix it myself if I knew enough to take it on.—PaulTanenbaum (talk) 05:02, 9 March 2014 (UTC)

Good point, I tried to trim the techno talk.--Smokefoot (talk) 15:04, 9 March 2014 (UTC)