| Abstract
| - A study of the regioselectivity of the photochemical [2+2] cycloaddition of triplet enones with a series ofground-state electron-rich and electron-poor alkenes using density functional theory (DFT)-based reactivitydescriptors is presented. Using the concepts of local softness combined with a local hard and soft acids andbases principle and a softness matching approach, the regioselectivity of this reaction can only be explainedin the case of the interaction of the triplet enones with electron-rich alkenes. In the next part, the regioselectivitywas assessed within the framework of conceptual spin-polarized conceptual DFT, considering response functionsof the system's external potential v, number of electrons N, and spin number NS (with NS being the differencebetween the number of α and β electrons in the spin-polarized system). Within this theory, the concepts oflocal spin philicity and donicity are introduced. Using the spin philicity concept, the regioselectivity canalmost be completely interpreted as resulting from the interaction of the site on the alkene with the highestspin philicity (i.e., lowest destabilization upon increasing spin number) with the site showing the highestchange of spin number on the enone expected to result in the largest stabilization of this species.
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