Alkane diradicals

Before we present the results of these calculations, it is useful to consider the expected results. Sulfur rings are isovalent to cycloalkanes (CH2)n and might be expected to have large gaps between the top filled and lowest empty orbitals. The sulfanes HSnH, formerly called polysulfides, would be expected also to have large gaps between the top filled and lowest empty orbitals in analogy to the isovalent linear alkanes. On the other hand, the open chain S allotropes are isovalent to alkane diradicals and would be expected to be colored. We considered also the possibility of branched chain allotropes, whose properties we could not predict in advance. The extended Hiickel calculation was used to see whether the expected properties were supported by the simplest model orbital calculation, to determine the dependence on number of sulfur atoms, and to see if branched chain structures are reasonable. Moreover,... 

It has been shown by ab initio calculations that the alkane oxidation proceeds via a highly polar asynchronous transition state, which is common for either concerted oxygen insertion into the C-H bond or formation of a radical pair [48c,d]. The transition state having considerable diradical character (and also is polarized) is shown below ... 

In most cases thermal or photochemical treatment of the azoalkanes is a pathway to the corresponding alkanes via the corresponding diradicals. This aspect is extensively covered by the reviews already cited. However, in some cases, the diradicals collapse in a different way. For example, Diels-Alder addition of cyclopentene derivative 486 to MTAD gives ura-... 

The spectrum yields some important insights into the type of species the liquid contains and into their reactivity. The fifth section shows that the red absorption indicates that liquid sulfur contains reactive chains because sulfur rings in analogy with alkanes are expected to be yellow and to absorb in the near ultraviolet, while sulfur chains in analogy with alkyl diradicals are expected to be colored deeply. 

E)-Alkenes. The reaction of trialkylboranes with alkaline silver nitrate (2, 368) to form coupled alkanes has been used to convert 1,2-diorganoboranes from internal alkynes into (E)-alkenes. The reaction is considered to involve an intermediate diradical that couples intramolecularly to the alkene. 

The same authors later studied the evolution of the radicals formed after rupture of a single knotted alkane molecule using first-principles molecular dynamics calculation [284]. In knotted chains, recombination of the radicals is totally bypassed in favor of ultrafast (about several hundred femtoseconds) phenomena such as diradicals which generate cyclic alkanes, and disproportionation to form carbon-carbon double bonds. Saitta and Klein suggested that the trefoil knot imposes topological constraints to the velocity distribution of the recoiling radicals at rupture, leading to deviations from the canonical recombination reaction. 

Reactions of the ground state, NH (X X ), play an important role in combustion processes. Triplet NH reacts with molecular hydrogen, water and CO2. Modem theoretical study demonstrates that reactions with H2 and H2O proceed via hydrogen atom abstraction. The NH abstracts hydrogen atoms from starting material, hydrazoic acid, and from hydrocarbons to form aminyl (NH2 ) and aUcyl radicals in spite of the fact that some reactions are endothermic, depending on the alkane. Absolute rate constants for many of these reactions have been measured in the gas phase. Triplet NH also reacts with aUcenes via formation of an intermediate triplet diradical which then decomposes into several reaction channels. ... 

Photo-decarboxylation Acyclic carbonyl diradical on decarboxylation give carbon monoxide, an alkene or a cyclic alkane or both. 

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