Divalent carbon compounds

The simplest diazo compound, diazomethane, undergoes loss of nitrogen in the gas or solution phase to yield a divalent carbon compound, methylene ... 

Carbenes are divalent carbon compounds, also known as methylene. They have neutral carbons with a lone pair of electrons, and are highly reactive. Methylene can be prepared by heat or light initiated decomposition of diazomethane (explosive and toxic gas). 

Here, too, reaction involves a divalent carbon compound, a derivative of methylene dichlorocarbene, CCl2. It is generated in two steps, initiated by attack on chloroform by the very strong base, /er/-butoxide ion, and then adds to the alkene. 

Divalent Carbon Compounds. There are a number of CRR species, generally called carbenes, which play a role in many reactions even though they are short-lived,5 A general means of generating carbenes is by photolysis of diazoalkanes this is done in the presence of the substrate with which the carbene is intended to react, such as an olefin ... 

The diazo reactions in this chapter are characterized by processes run either in the gas phase, in relatively inert matrices, or in — typically, but not exclusively — aprotic and comparatively apolar solvents, either thermally or photolytically or with transition metal catalysis of various types. The metastable intermediates are carbenes (RR C ), i. e., neutral, apparently divalent, carbon compounds, or their transition metal complexes (coined carbenoids, see later in this section). It is interesting to recall that the synthesis of a compound that we now call a carbene, namely methylene (H2C ), was already attempted in the early 19th century, i.e., before the tetravalency of carbon was established. Dumas (1835) and Regnault (1839) thought then that it should be possible to obtain a compound consisting of one carbon and two hydrogen atoms by dehydration of methanol (a compound of which only the atomic ratio 1C 4H lO was then known). ... 

The electronic structures of a range of compounds (acyclic, cyclic and heterocyclic) have been explored by DFT calculations. It was more specifically shown that the charge of the divalent carbon compound exhibit the main contribution to the tr basicity (related to the a donor strength) followed by the nature of the atom a to the divalent carbon. This effect has been shown to propagate along the chain. The nature of the n system is less related to the structural nature of the molecules but fits well with the description of the n molecular orbitals which explain both the n acidity and the n basicity. 

---