Oxyallyl diradical

The short lifetimes of carbon-centered monoradicals are generally reduced in the case of diradicals due to their propensity to form covalent bonds. It has been suggested that stable diradicals may be observable from highly strained bicyclic molecules where the TS for inversion is a diradical. Unfortunately, only persistent diradicals have been obtained in this way. Akin to this approach, in a recent attempt to generate the oxyallyl diradical, Sorensen and co-workers synthesized two substituted bicyclobutanones hoping to stretch and homolytically break the central bond using bulky substituents, which would also stabilize the diradical. Though the bicyclobutanones did not yield the desired oxyallyl derivative, the X-ray structures showed... 

Related to TME is TMM 34. The lale of TMM also entails a synergistic interplay of theory and experiment similar to that of TME. This story is nicely retold in the review article of Lineberger and Borden. Instead of reviewing this TMM story, we present the case of the analogous oxyallyl diradical (OXA) 40. This diradical has been proposed as an intermediate in the ring opening of cyclopropanone " and other reactions. 

Figure 5.11 MOs of oxyallyl diradical 40. (See insert for color representation of this figure.)...

Simsa, D. Demel, O. Bhaskaran-Nair, K. Hubac, I. Mach, R Pittner, J. Multireference coupled cluster study of the oxyallyl diradical, Chem. Phys. 2012,401, 203-207. 

Solomek T, Heger D, Ngoy BP, Givens RS, Klan P (2013) The pivotal role of oxyallyl diradicals in photo-Favorskii rearrangements transient spectroscopic and computational studies. J Am Chem Soc 135 15209-15215... 

The introduction of heteroatoms into the hydrocarbon diradicals is a frequently applied strategy to tune the spin preference and relative stabilities of diradicals. The heteroatoms may change the energies of donor or acceptor orbitals, and consequently affect the donor-acceptor interaction involved in the cyclic orbital interaction. Take 2-oxopropane-l,3-diyl, or so-called oxyallyl (OXA, 18) as an example [29]. It is a hetero analog of TMM, as shown in Fig. 14. The replacement of CH with oxygen in the central fl unit leads to a decrease in energies of Jt and k orbitals. This may enhance the orbital interaction through one path (denoted by bold lines) and weaken that via the other (denoted by wavy lines) relative to the continuous cyclic orbital interaction in the parent species 1 (Fig. 14). As a result, the p-Jt -q... 

Finally, in some cases diradical negative ions can even be generated directly npon ionization of appropriate precnrsors. For example, nitrene and carbene anions can be formed by El of organic azides, diazo-compounds, and diazirines, whereas Branman and co-workers have reported the formation of oxyallyl anions by El of flnorinated acetyl componnds (Eq. 5.12). ... 

In 2009, Lineberger and Borden " reported the photoelectron spectrum of the oxyallyl radical anion, with more complete analysis provided in 2011. " They observed two sets of peaks in the spectrum, one originating at 1.942 eV and the second at 1.997 eV. This second set has rather sharp peaks with a progression of 405 cm B3LYP/6-311++G(d,p) computations of the OXA radical anion and triplet diradical show a large difference in the C-C-C angle of these two structures (121.9° and 114.4°, respectively). The vibrational frequency of the C-C-C bend is computed to be 408 cm in excellent agreement with the PES. 

The oxyallyl system, another reactive intermediate usually written with two charges 6.370 instead of as a diradical, has a similar conjugated system, except that the coefficients will be different, and the central carbon atom, although close to a node in ip2 and u>3, will not have a node exactly through it. When generated on its own, it dimerises with different regioselectivity from trimethylenemethane, giving the 1,4-dioxan 6.371.875... 

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