Talk:Conjugated system

message: In the beta-carotine example shown, the double bonds are all cis.  In Conjugated linoleic acid, the bonds are trans.  Does cis / trans alignment have an effect on the conjugation? David.Throop 18:42, 28 November 2006 (UTC)
replies: text: It may have an effect (stability, UV absorbance, etc) but does not affect the designation of something as being "conjugated". DMacks 18:54, 28 November 2006 (UTC)

text: The reason that possible alignments are only cis/trans, rather then having the third bond go out of the page is that due to conjugation three such bonds tend to be in the same plane. The cis and trans alignments have different conjugation-energies, and in this sense they effect conjugation. Cederal 14:41, 17 December 2006 (UTC)
thread_title:  Cis or Trans? 

message: Why do conjugated systems require less energy to reach the excited state? That's what I came here to find, but there's no mention of the reason behind this trend. Thinking about the delocalized nature of the electrons, it seems plausible to say that they have a weaker attachment to their ground states and thus require only a little energy to reach the excited state. Hopefully someone can expand upon this in the article. Richard001 05:58, 6 May 2007 (UTC)
thread_title: Conjugated systems and energy required for excited state

message: In normal (planar) conjuaged molecules, each atom in the system possesses a p-orbital, as the article says. What about linear molecules, such as cumulenes and polyynes, in which each atom in the chain possesses two p-orbitals instead of one? Is there a special name for this sort of thing? If so, what is it? Stonemason89 (talk) 20:55, 11 September 2008 (UTC)
replies: text: The conjugated system still involves only one p orbital on each atom. What the other orbitals are doing and how the atoms are hybridized? Not so relevant...those orbitals are pointing in different directions, so there's little/no overlap with those in the conjugated system. It's just like how a triple bond has two essentially independent pi systems. In 1,2,3-butatriene, the Δ1,2 and Δ3,4 bonds are conjugated, involving those p atomic orbitals that compose the double bonds. The Δ2,3 bond is composed of different p atomic orbitals on those sp-hybridized than the other double bonds, so it is perpendicular to the other two double bonds. Therefore, this pi system is not in conjugation with the others. DMacks (talk) 21:17, 11 September 2008 (UTC)
replies: text: Guess we need to rewrite the lede a bit. Otherwise even things as "undergrad orgo" as benzyne are troublesome. DMacks (talk) 21:19, 11 September 2008 (UTC)
replies: text: So let me try to understand this publicly. The two different pi systems are independent from each other, that is clear. But how does that affect the system is still an open question. If I can suggest, I guess that the double pi system forces the bond to be linear, in exchange for the pi conjugation and the long range stabilization effects that you can observe in 120º Csp2 conjugated systems. I say this as conjugation has been seen to be almost negligible in alkyne bonded systems. Euderminio (talk) 10:47, 25 March 2022 (UTC)
replies: text: Plus, the initial question referred to a common name for cumulenes and polyynes which is still an open question. Euderminio (talk) 10:48, 25 March 2022 (UTC)
thread_title: Doubly conjugated molecules?

message: I am totally confused by this.  It is confusing to include homoconjugation here, IMHO. Either too much or not enough.
I am confused enough by systems like c=c=c-c=c and c=c=c-c=c=c →  conjugated?
How about C≡C-C≡C ?  A double bond is not the only type of C.C pi bond.
How about CN-c=c ? OCN-c=c ?  NC-c=c ? (etc.)  This article gives no guidance.
As far as "tub shaped"  - 40 years a chemist, don't recall ever hearing the term.
Too bad there aren't terms like "concave" that would better describe the shape, huh?
You really have to make up your mind.  Is conjugation an experimental fact or a theoretical fact?
If experimental, how is it determined/measured?
If theoretical, how is the determination made that there is enough "pi" character to the intervening single bonds to characterize the system as conjugated? Given that most modern calculations are DFT based, is the use of Molecular Orbitals appropriate?216.96.76.236 (talk) 02:36, 23 June 2013 (UTC)
thread_title:  Incomplete II 

message: I am a bit concerned about describing conjugation in terms of single and double bonds.
I thought the whole point about conjugation is that these are NOT single and double bonds, but an intermediate form, and each bond is equal to all the others (rather than some being single and some double). 
In addition, atomic orbital terminology is used (e.g. p-orbital) when it might be better to use molecular orbital terminology. In fact the article seems unsure as to which to use, as there are phrases discussing such things as "pi electrons" and "p orbitals" in the same sentence.
Marchino61 (talk) 05:54, 1 September 2013 (UTC)
replies: text: It is true that the bonds are intermediate for aromatic molecules such as benzene, which has two conjugated structures of equal importance, so that the true wave function has six equivalent CC bonds which are intermediate between single and double bonds. I have now included this point in the article. For butadiene, however, there is a unique conjugated structure with C=C and C-C bonds which approximately represent reality, and the effects of conjugation constitute a correction so that the C-C bond is stronger and shorter than a normal C-C bond. Dirac66 (talk) 21:00, 23 July 2015 (UTC)

text: Actually the total wave function of any polyatomic molecule can be written in terms of delocalized MO's, but for many molecules (such as alkanes) the dominant Lewis structure is a quite good approximation to reality without adding any minor structures. The question is how important are the minor structures in conjugated systems such as butadiene, especially since they are ionic structures (as shown in your link to ChemVista). It is clear that they are more important in butadiene than in ethane, but also that they are less important than in benzene. We could mention the ionic structures in the article, but I would prefer to have an additional source such as a quantum-mechanical study which gives a quantitative idea of their importance. Dirac66 (talk) 14:31, 26 July 2015 (UTC)
thread_title:  Alternating Single and Double Bonds? 

message: Substituted at 12:10, 29 April 2016 (UTC)
thread_title: Assessment comment