ESR.‐Studies of Nonalternant Radicals Structurally Related to Phenalenyl

The radical anion and the radical cation of azuleno[1,2,3‐ cd ]phenalene (III) have been investigated by ESR. spectroscopy, along with the radical anion of 2‐phenylazulene (IV). Also studied has been the neutral radical obtained by one‐electron reduction of cyclohepta[cd]phenalenium‐cation (VI ⊕ ). Assignment of the proton coupling constants for the radical ions III. ·⊖, III ·⊕ and IV·⊕, and the radical VI · is supported by comparison with the ESR. spectra of specifically deuteriated derivatives III‐d 5 ·⊖, III‐d 5 ·⊕, IV‐d 2 ·⊖ and VI‐d 1 ′. The experimental results are in full accord with qualitative topological arguments and predictions of HMO models. Whereas the radical anion III ·⊖ exhibits α‐spin distribution similar to that of IV ·⊖the corresponding radical cation III ·⊕ and the neutral radical VI · are related in this respect to phenalenyl (V·). It is noteworthy that oxidation of III by conc. H 2 SO 4 yields a paramagnetic species (IIIa ·⊕) which has a similar – but not an identical – structure as the radical cation III ·⊕ produced from III with AlCl 3 in CH 3 NO 2 .