To quote from Wikipedia: in chemistry, a carbene is a molecule containing a neutral carbon atom with a valence of two and two unshared valence electrons. The most ubiquitous type of carbene of recent times is the one shown below as 1, often referred to as a resonance stabilised or persistent carbene. This type is of interest because of its ability to act as a ligand to an astonishingly wide variety of metals, with many of the resulting complexes being important catalysts. The Wiki page on persistent carbenes shows them throughout in form 1 below, thus reinforcing the belief that they have a valence of two and by implication six (2×2 shared + 2 unshared) electrons in the valence shell of carbon. Here I consider whether this name is really appropriate.
Posts Tagged ‘Functional groups’
How does an OH or NH group approach an aromatic ring to hydrogen bond with its π-face?
Wednesday, June 22nd, 2016I previously used data mining of crystal structures to explore the directing influence of substituents on aromatic and heteroatomatic rings. Here I explore, quite literally, a different angle to the hydrogen bonding interactions between a benzene ring and OH or NH groups.
Why is the carbonyl IR stretch in an ester higher than in a ketone: crystal structure data mining.
Saturday, June 18th, 2016In this post, I pondered upon the C=O infra-red spectroscopic properties of esters, and showed three possible electronic influences:
Azane oxide, a tautomer of hydroxylamine.
Friday, April 15th, 2016In the previous post I described how hydronium hydroxide or H3O+…HO–, an intermolecular tautomer of water, has recently been observed captured inside an organic cage[1] and how the free-standing species in water can be captured computationally with the help of solvating water bridges. Here I explore azane oxide or H3N+-O–,‡ a tautomer of the better known hydroxylamine (H2N-OH).
References
- M. Stapf, W. Seichter, and M. Mazik, "Unique Hydrogen‐Bonded Complex of Hydronium and Hydroxide Ions", Chemistry – A European Journal, vol. 21, pp. 6350-6354, 2015. http://dx.doi.org/10.1002/chem.201406383
I’ve started so I’ll finish. Kinetic isotope effect models for a general acid as a catalyst in the protiodecarboxylation of indoles.
Sunday, January 10th, 2016Earlier I explored models for the heteroaromatic electrophilic protiodecarboxylation of an 3-substituted indole, focusing on the role of water as the proton transfer and delivery agent. Next, came models for both water and the general base catalysed ionization of indolinones. Here I explore general acid catalysis by evaluating the properties of two possible models for decarboxylation of 3-indole carboxylic acid, one involving proton transfer (PT) from neutral water in the presence of covalent un-ionized HCl (1) and one with PT from a protonated water resulting from ionised HCl (2).
π-Resonance in thioamides: a crystallographic “diff” with amides.
Saturday, September 5th, 2015The previous post explored the structural features of amides. Here I compare the analysis with that for the closely related thioamides.
π-Resonance in thioamides: a crystallographic "diff" with amides.
Saturday, September 5th, 2015The previous post explored the structural features of amides. Here I compare the analysis with that for the closely related thioamides.