Abstract
In Chap. 5 it was assumed that in planar conjugated radicals the proton hyperfine splittings are proportional to the unpaired π-electron density on the carbon atom adjacent to the proton. That is
Isotropic proton hyperfine splittings were shown in Chap. 3 to arise when there is a net unpaired-electron density at the proton. In π radicals, the unpaired electron resides in a π-molecular orbital constructed from a linear combination of 2p z carbon atomic orbitals. However, each 2p z orbital has a node in the plane of the molecule. Since this plane also contains the protons, there should be no unpaired-electron density at the proton and hence no hyperfine splitting. In spite of this node, the numerous spectra in Chap. 4 demonstrate that isotropic proton hyperfine splittings do occur in π radicals.
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Wertz, J.E., Bolton, J.R. (1986). Mechanism of Hyperfine Splittings in Conjugated Systems. In: Electron Spin Resonance. Springer, Dordrecht. https://doi.org/10.1007/978-94-009-4075-8_6
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DOI: https://doi.org/10.1007/978-94-009-4075-8_6
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