Wikipedia:Reference desk/Archives/Science/2024 March 15

= March 15 =

Can't remember the name of this organic chemistry phenomenon where conjugation "extends" a functional group
I think I remember reading a Wikipedia article about this, but I can't find the name of this phenomenon at all. Pinging maybe you might know since you are an active editor of organic chemistry articles. Here I have drawn the concept:



This is the phenomenon in which a double bond "extends" a functional group by conjugation, so that it behaves similarly to the parent functional group. The bottom compound, an "extended" carboxylic acid, has similar chemistry as the top carboxylic acid, except the two parts of the functionality (C=O and -OH) are separated by an additional double bond. The reason for this similarity is because conjugation can transfer charges by resonance, e.g. the bottom compound is acidic like a carboxylic acid because the negative charge on the deprotonated -OH oxygen can move to the carbonyl oxygen by resonance. Michael7604 (talk) 05:50, 15 March 2024 (UTC)
 * See or search dicarbonyl or keto-enol equilibrium. . --Smokefoot (talk) 14:37, 15 March 2024 (UTC)
 * @Michael7604 You already had the key concept in your title: see conjugated system and the articles linked from it. My favourite related topic is, of course, the Michael addition reaction. Mike Turnbull (talk) 16:28, 15 March 2024 (UTC)
 * A vinylogous group. DMacks (talk) 18:26, 15 March 2024 (UTC)
 * This is it, thank you Michael7604 (talk) 21:15, 15 March 2024 (UTC)

Fictitious force. Is the opposite phenomenon called a: "Real" force? "Physical" force? "External" force? "Natural" force?
I'm looking for the most useful term, intended to exclude fictitious forces. HOTmag (talk) 08:38, 15 March 2024 (UTC)
 * Each of the suggested terms is usable if you take away the ornamentation of Scare quotes. Philvoids (talk) 10:31, 15 March 2024 (UTC)
 * They should only be considered to be quotation marks. That's because I was looking for "the most useful term" (Btw now I'm quoting myself), i.e. a term that could be quoted from sources using useful terminology. HOTmag (talk) 10:45, 15 March 2024 (UTC)
 * A commonly used contrasting term is true force. --Lambiam 17:25, 15 March 2024 (UTC)
 * Meh. Yes, true force has some popularity, sometimes even in quotes, but don't expect everybody to understand you when you mention true forces. And despite Newton's ideas on absolute space and preferred reference frames that only have constant velocity relative to it, in real life we deal with the equivalence principle, under which those fictitious forces are as real as gravity. Which is quite real in classical mechanics. In fact, they are gravity. In a free-falling lift, we just declare gravity zero. On a merry-go-round, we just declare the centrifugal force and Coriolis force part of gravity. Good luck describing orbital manoeuvring or accretion in compact binaries in an inertial frame. General Relativity (I think you'll love that) even makes it its basic principle. Turns out that the entire universe spinning around our stationary merry-go-round causes frame dragging, which exactly matches those fictitious forces. PiusImpavidus (talk) 19:57, 15 March 2024 (UTC)
 * That was Einstein's original view, but I think the matter has become somewhat controversial. We have an article on Mach's principle. --Trovatore (talk) 21:06, 15 March 2024 (UTC)
 * Just as a slight extension, in dynamics we invent a fictitious force m*a, called a D'Alembert force, and can then treat it as a statics problem. It isn't always useful. Greglocock (talk) 23:36, 15 March 2024 (UTC)