|WikiProject Chemistry||(Rated C-class, High-importance)|
singlet/triplet labels in carbene addition reaction
Is it me, or are the labels for singlet and triplet reversed in the carbene addition to the alkene reaction? The singlet should be the top, concerted, stereospecific reaction, correct? That's what the text implies... Ed Sanville 07:12, 14 January 2006 (UTC)
I think the top one should be the singlet, at least according to the text. (unsigned comment)
- Fixed. DMacks 02:30, 23 February 2006 (UTC)
I think 'further research' remarks like:
- Further studies are being conducted in order to test the effects of added substituents onto the carbene. These studies are being conducted at the University of California, Irvine School of Physical sciences. <!-- need actual cite here -->
should not be in the original text. Probably more groups are studying these systems. --Dirk Beetstra 08:33, 10 May 2006 (UTC)
- Concurred. Actually, that whole sulfinyl carbene can probably be removed, since there's nothing notable mentioned about it. There's no citation other than an institution name, the only reference at uci.edu I can find about it is that an undergrad is working on it this year, and there's no ACS publication by the PI (Freeman) about it. And the IP maps to uci also. Sounds suspiciously like the guy is reporting his own original research. DMacks 15:00, 10 May 2006 (UTC)
- Hmmm, I did not read it like that, yet. Indeed, I guess the whole section can be removed. It is 'just another carbene' where some group is currently working on, I will move it here:
- Another example of a carbene is methanesulfinyl carbene, molecular formula CHS(O)CH<sub>3</sub>, having a hydrogen and a sulfinyl (S(O)CH<sub>3</sub>) group bound to the sp<sup>2</sup> carbon. Using the Density Functional B3LYP method with a 6-31G+(d) basis set, calculations indicate that the triplet state of this molecule is more stable than its singlet counterpart.<!-- references needed here -->
- Cheers, Dirk Beetstra 15:53, 10 May 2006 (UTC)
Carbenes, Persistent carbenes, NHC's ??
I was informed that 'persistent carbenes' (a section in the main article) was a candidate for a seperate article later on (that is, when it was big enough).
Somehow I feel that it might be a good plan to split of a part, but I would then like to suggest to make a seperate article about the N-Heterocyclic Carbenes (and the like). To me the subject/term 'persistent carbene' belongs in this article (because, persistent is a relative measure, for someone studying a compound by NMR, persistent is several minutes, for a laser-spectroscopist, femtoseconds are already long enough). The NHC's, on the other hand, grow into a seperate group of organic molecules (and there are even organometallic analogues, the silylenes and germylenes), with their own chemistry, and they get extensively used nowadays in organometallic chemistry as ligands. I'd like to hear some pro's and con's before starting to move things around.
By the way, I noticed that there is already an article Transition metal carbene complex (I don't know if I would search it there ..). This one might also be taken into consideration in this discussion (I'll make a link from the talk-page of that page). Dirk Beetstra 21:35, 11 May 2006 (UTC)
- The History of stable carbenes is a great addition to this article, two remarks though: the persistent carbenes are ready for a spin-off and an article of their own, like suggested in the discussion above. Also the link density is poor: by linking keywords in the text to other articles the article will improve and also become unstandable for less chemistry-experienced readers V8rik 20:40, 10 August 2006 (UTC)
Reminders to editors
Please use the Edit summary field to document what changes you are making. A stream of blank-summary changes from an anon-IP is a common sign of vandalism...help your worthwhile changes get the respect they deserve:) Which leads me to my other suggestion: if you're going to be doing a log of Wiki editing, consider creating an account and log in so that edits are associated with a specific editor instead of an IP. Multiple editors could have the same IP and any given editor might use several different IPs. DMacks 16:26, 11 August 2006 (UTC)
nonlinear triplet ground
In the section on bonding it is stated this is the ground state for carbenes. And than a series of exceptions is mentioned. To what part of the statement are they exceptions? Are they
- linear and singlet?
Stabilisation of triplet carbenes with SiF3
"in accord with Si's electronegativity, these carbenes exhibit the largest Te values [...] the dependence of Te on the choice of β-substituents is the least pronounced in the series of silyl carbenes"
"In searching for electronically stabilized triplet ground state carbenes, one should thus focus on silyl carbenes. Furthermore, SiF, SiO, and SiCl substitution provides exceptional kinetic stability toward homolysis and rearrangement. While 3C(SiF3)2 should be the global minimum on the PES of respective stoichiometry, sterically demanding siloxy-substituents appear to be the most promising to facilitate kinetic stability toward inter- and intramolecular reactions." Tomásdearg92 (talk) 05:08, 30 October 2013 (UTC)
Hi Tomásdearg92, the group electronegativity of -SiF3 is around 3.5, so its almost as eletronegative as fluorine (EN = 4, both on th Pauling scale). Si itself is of course more electropositive then C, true. But that is not a matter of debate here. If you read the text carefully, you will realize that it was stated nowhere there that -SiF3 substitution leads to stable triplett carbened because of its high electropositivity! -SiF3 supports stable triplett carbenes (for kinetic reasons) and Si functions in general are more electropositive than homolgous C functions and electropositive substituents may stabilize triplett carbenes. That might be all true. But its is certainly not true that -SiF3 is a strongly electropositive substituent and it is also not true that SiF3 stabilizes triplett carbenes due to its electropositivity. And if you read careful enough you find that this is stated nowhere in your reference. The passge in the article is wrong and very confusing, and the lonely primary literature reference might not be the best choice for referenceing an encyclopedian article, I would suggest. Secondary literature would be strongly preferred. Cheers --220.127.116.11 (talk) 12:52, 4 November 2013 (UTC)
- Firstly, I agree, secondary literature is always preferred. But that reference covers both claims preceding it, which is why I initially jumped to bring it (the reference, not the trifluorosilyl part) back. Scifinder tells me that this paper has been cited in at least 5 reviews, the DOIs (10.1007/128_2008_18) and (10.1016/j.ccr.2008.05.018) point to the most highly cited of those.
- Also agreed, nowhere in the source does it suggest that the label electropositive should be affixed to the -SiF3 group, I tried to make the sentence clearer, but I likely failed in that regard. Electropositive is meant to refer to the silicon atom itself, as opposed to the trifluorosilyl group as a whole, and was reflecting both the previous description and the source. (Which isn't mine, I've been editing this article only slightly longer than your IP has).
- However, if the passage is very misleading, I implore you to correct it. No one else will. What I read from the source is that σ-donors (such as Si) that do not engage in π/p-effects such as hyperconjugation (through strong Si-X bonds), with high symmetry (-SiX3) will thermodynamically stabilise triplet carbenes. Bulkier substituents, on the other hand, may kinetically stabilise triplet carbenes by impeding dimerisation. Am I correct?
- - Tomásdearg92 (talk) 07:49, 5 November 2013 (UTC)