Talk:Aldehyde

pKa
The pKa of an α hydrogen is 20.

NOTE: Where did that pKa come from? Is it aliphatic or aromatic, as benzaldehyde would stand to have a lower pKa (as it is more acidic that the aliphatic version).


 * Benzaldehyde has no alpha proton, so it is not acidic, do you mean phenylacetaldehyde? I don't have the source of this value to hand, but I do have a reference for 3-pentanone as pKa 19-20 in water.    See here I suspect that the higher figure you have seen is in DMSO, where pKa values are usually higher than in water. Walkerma 21:01, 20 September 2005 (UTC)

how does an organism metabolize an aldehyde?

nomenclature
in the wikipedia article on the "IUPAC nomenclature of organic chemistry" it is stated that (quote): " If a prefix form is required, "oxo-" is used (as for ketones), with the position number indicating the end of a chain: CHOCH2COOH is 3-oxopropanoic acid. If the carbon in the carbonyl group cannot be included in the attached chain (for instance in the case of cyclic aldehydes), the prefix "formyl-" or the suffix "-carbaldehyde" is used: C6H11CHO is cyclohexanecarbaldehyde. "

This article doesn't mention the prefix "oxo-" at all. Instead only: " If another functional group is present which IUPAC rules prescribe must be named as a suffix, the aldehyde group is named with the prefix formyl-. This prefix is preferred to methanoyl-. "

This would imply that either this article on aldehydes misses out important information, or that the above quoted article on IUPAC nomenclature is misleading.

In any case there is a lack of clarity. Could somebody more qualified please look into this? —The preceding unsigned comment was added by 203.81.207.114 (talk • contribs) 20:45, 11 June 2007 (UTC)
 * The Aldehyde article has been revised. Spacepotato 09:26, 4 August 2007 (UTC)

acyl vs aldehyde
Are they exactly the same thing?199.76.186.8 15:12, 22 September 2007 (UTC)
 * No, they are different - rather like the difference between alkyl and alkane. So you could talk about the acyl group in acetic acid, meaning the CH3C(=O)- group, commonly called the acetyl group. Walkerma 15:38, 22 September 2007 (UTC)

What is a semialdehyde?
What is a semialdehyde, have seen it e.g. here: Succinic_semialdehyde  ChristianBxx 16:05, 22 October 2009 (UTC)  —Preceding unsigned comment added by Christian75 (talk • contribs)


 * A simple internet search reveals that it is the monoaldehyde of a dicarboxylic acid. --98.162.248.133 (talk) 05:20, 27 June 2013 (UTC)

Reactions
The Aldol Condensation and Canizzaro reactions need more coverage here since they are important reactions concerning Aldehydes. Could someone please pick excerpts and put them here? 02:09, 8 April 2010 (UTC)Darshit —Preceding unsigned comment added by Darnir redhat (talk • contribs)

Merger proposal
I propose that Dialdehyde be merged into Aldehyde. I think that the content in the dialdehyde article can easily be explained in the context of aldehyde, and the aldehyde article is of a reasonable size in which the merging of dialdehyde will not cause any problems as far as article size or undue weight is concerned. Roshan220195 (talk) 18:08, 29 March 2012 (UTC)

Unsaturated aldehyde
This phrase comes up a bit, and is used in this article on Coriander, NPR story about how people taste cilantro/coriander (December 2008). Should this be defined here more specifically?(mercurywoodrose)76.254.38.113 (talk) 03:32, 24 September 2012 (UTC)

Assessment comment
Substituted at 07:08, 29 April 2016 (UTC)

Technical approach
I miss an introductory description of an aldehyde as a functional kind of molecule, which has certain characteristics, a description accessible to the general reader. The configuration of orbitals, etc., should be way down the article; this is the technical part of interest to the specialist. Cl ea n Co py talk 16:01, 11 November 2020 (UTC)

picture above - missing
Under "Structure and bonding" we have: "Because of resonance stabilization of the conjugate base, an α-hydrogen in an aldehyde (not shown in the picture above)..."

The "picture above" seems to be missing. I've looked at the article in Chrome, Firefox and Slimjet on Ubuntu 18.04. In none of them is there a picture showing above the Structure and bonding section. Hedles (talk) 09:34, 18 November 2020 (UTC)

Non-acidity of RC(O)-H
I removed this large section. Maybe others disagree, but this non-reactiion does not usually figure into discussions of aldehydes. But maybe there is useful info here. "The formyl proton itself does not readily undergo deprotonation. The anionic species formally derived from deprotonation of an aldehyde proton, known as an acyl anion, is highly unstable and must be kept at low temperatures.  In fact, with the exception of certain hindered dialkylformamides, the synthesis of acyl anions by direct deprotonation is not a feasible route, since the deprotonated species will almost immediately add to the highly reactive carbonyl of the starting material to form an acyloin compound.  For this reason, the acidity of the formyl proton is difficult to measure.  In the case of HCONiPr2, the acidity of the formyl group was found to be very close to that of diisopropylamine (pKa ~ 36).  The gas-phase acidity of aldehyde was found to be 393 kcal/mol, making it more acidic than hydrogen (400 kcal/mol) and ammonia (402 kcal/mol), but less acidic than water (390 kcal/mol) in the gas phase.

At around 85 kcal/mol, the formyl C–H bond is weaker than that of a typical bond between hydrogen and an sp2-hybridized carbon. Thus aldehydes are prone to undergo hydrogen-atom abstraction in the presence of free radicals, a fact accounts for the ease with which aldehydes undergo autoxidation." --Smokefoot (talk) 13:57, 13 December 2021 (UTC)