Singly occupied molecular orbital compounds

The presence of an unpaired electron in radical cations has significant consequences for symmetric compounds. This becomes clear if one considers the transformation of an open shell symmetric compound into another compound of a different symmetry. In such cases, the symmetry of the singly occupied molecular orbital (SOMO) determines the overall electronic states of the reactant and the product. If the two electronic states do not correlate, i.e., do not share a common symmetry element, a symmetry-preserving pathway from reactant to product is not possible. Any adiabatic reaction leading from the reactant to the product therefore has to involve the loss of symmetry. This problem obviously does not occur for the case of closed-shell molecules, where all orbitals are doubly occupied, leading to a common electronic Ai state for all molecules. 

Radical anions of haloaromatic compounds are proposed to be intermediates in different type of reactions. Their fragmentation rates, determined electrochemically [300] or by pulse radiolysis [301] range from lO " s for phenyl halides to 10 s for some halonitrobenzenes. The rate of the reaction for some aryl hahde radical anions is too high to be measured electrochemically, the fragmentation of more stable radical anions such as those of 1-bromo- and 1-iodoanthraquinone [302], p-[303] and m-bromo- [304] and p- [303] and w-chloronitrobenzenes [304] occurs at considerably lower rates and the reaction is favored from their photoexcited state. Aryl halide radical anions may present a-n orbital isomerism depending on the orbital symmetry of their singly occupied molecular orbital [305], a proposal derived from theoretical and experimental evidences [306]. The isomerism is possible... 

SOMO Activation Within the field of aminocatalysis, asymmetric organo-SOMO (singly occupied molecular orbital) catalysis has recently emerged as a powerful technique for the preparation of optically active compounds. In this context, MacMillan and coworkers described in 2008 the formation of y-oxyaldehydes from aldehydes and styrenes by organo-SOMO catalysis [25]. The condensation between the amine catalyst 46 and an aldehyde gave rise to an enamine intermediate, which was then oxidized by ceric ammonium nitrate (CAN) to give a radical cation. Reaction of this radical cation with a nonactivated olefin, namely styrene, led to the... 

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