Physical-Organic Photo-chemistry. III. Photooxidations

  • David Phillips
Part of the NATO Advanced Study Institutes Series book series (NSSA, volume 25)


We are concerned here with the reactions of electronically excited states with oxygen, and those of electronically excited states of oxygen with substrates. Figure 1 shows the electronic energy levels of the three lowest states of molecular oxygen along with those of other molecules of interest, and Figure 2 the distribution of electrons in the πg*(2p) antibonding orbitals in the three states. The \(^3 \sum {_g ^ - } \) ground state is radical in character, whereas the \(^1 \Delta _g \) state, some 22.5 k cal mol−1 above the ground state, can be considered to be a dienophile because of the vacant πg orbital. \(0_2 \left( {^1 \Delta _g } \right)\) is reactive, and has a typical solution phase lifetime of 10−4–10−6 s. The second excited singlet state \(\left( {^1 \sum _g ^ + } \right)\), 37.5 k cal mol−1 above \(^3 \sum _g ^ - \) does not have the vacant orbital as does the \(^1 \Delta _g \) state, and thus cannot participate in two-electron processes. In any case, the solution phase lifetime of O2 \(\left( {^1 \sum _g ^ + } \right)\) is ~ 10−8 s, the species usually decaying to O2 \(\left( {^1 \Delta _g } \right)\), and thus it is the chemistry of this species which tends to dominate in photooxidations.


Excited State Excited Singlet State Chain Oxidation Antibonding Orbital Electronic Energy Level 
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Suggested Further Reading

  1. ‘Proceedings of International Conference on Singlet Oxygen and Related Species in Chemistry and Biology’, Pinawa, Canada, 1977.Google Scholar

Copyright information

© Plenum Press, New York 1979

Authors and Affiliations

  • David Phillips
    • 1
  1. 1.Department of Chemistry, The UniversitySouthampton UniversitySouthamptonUK

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