There are some non-classical carbocations, such as the 2-norbornyl cation, in which the positive charge is heavily delocalised. Have non-classical carbanions also been discovered? I have not seen any non-classical carbanions in books. If there are any non-classical carbanions, please provide some examples.
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asked Dec 16, 2018 at 10:20
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2 Answers
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Interesting question. It is much less studied and reported on than the case of non-classical carbocations, but I did find a few papers. Brown and Occolowitz (Ref.1) reported that deuterated bicyclo[3.2.1]octa-2,6-diene 1b, below, undergoes base-catalysed de-deuteration (potassium tert-butoxide in DMSO) to give 1a much faster (ca. $3 \times 10^4$) than the bicyclo[3.2.1]octa-2-ene counterpart, i.e. 2b $\rightarrow$ 2a. They suggested this is evidence for the intermediacy of a 6π-electron, delocalised (non-classical) carbanion 3.
![bicyclo[3.2.1]octenes](https://i.sstatic.net/Q33pa.png)
Much more recently, Brown reviewed and provided additional DFT computational evidence for stabilisation and charge delocalisation in these species (Ref.2).
References:
- J. M. Brown, J. L. Occolowitz, “A non-classical carbanion,” Chem. Commun. (London) 1965, (16), 376-377 (https://doi.org/10.1039/C19650000376).
- John M. Brown, “Origins of Stabilization and Evidence for Charge Delocalization in the Bicyclo[3.2.1]octadienyl Anion and Related Species,” Australian Journal of Chemistry 2014, 67(9), 1296-1300 (https://doi.org/10.1071/CH14244).
Mathew Mahindaratne
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answered Dec 16, 2018 at 13:46
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$\begingroup$ Can one unselect an accepted answer?? $\endgroup$– MicelleCommented May 15, 2020 at 17:41
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In addition to the species mentioned in the answer above, I found another one in Organic Chemistry by Morrison and Boyd(Seventh Edition)
answered Dec 16, 2018 at 16:09
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1$\begingroup$ Please give me some references $\endgroup$ Commented Dec 16, 2018 at 16:32