Radical anions doublet ground state

The situation is different for radical ions in which the unpaired electron is situated in a degenerate (or nearly degenerate) MO (Figure 5.12, right). Here, the doublet ground state of the radical ion will be degenerate (or nearly degenerate) and the lowest excited state may be one with three unpaired electrons. Indeed, quartet states and quartet —> doublet phosphorescence of such systems have been observed, for example, for the decacyclene radical anion,440 441 or for the radical cations of acetylene and benzene.442,443... 

While NO is a free radical with a doublet ground state, and therefore involved in several radical reactions, HNO has a singlet ground state (47,48). It is a weak acid with an accepted pi a of 11.4 (37,49). Interestingly enough, its anion, NO , has a triplet ground state (50,51), the same as the isoelectronic O2 molecule. Therefore, loss of a proton from HNO is not a simple acid/ base equilibrium but a spin-forbidden slow deprotonation (Table I, Eq. (8)) (37) ... 

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