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The Radical Anion of 2,7‐Diazapyrene, a Change in Orbital Sequence on Protonation
Author(s) -
Bruhin Jürg,
Gerson Fabian
Publication year - 1975
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19750580822
Subject(s) - chemistry , protonation , electronegativity , antibonding molecular orbital , ion , radical ion , proton , coupling constant , crystallography , atomic orbital , photochemistry , computational chemistry , organic chemistry , electron , physics , quantum mechanics , particle physics
ESR.‐spectra are reported for the radical anion I · Θ of 2,7‐diazapyrene (I), along with those for the radical cations I(2H) · ⊕ and I(2 CH 3 ) · ⊕ of 2,7‐dihydro‐2,7‐diazapyrene and its 2,7‐dimethyl‐derivative, respectively. In contrast to the analogous radical ions of 4,4′‐bipyridyl (II) and other previously studied diazaaromatic compounds, there is a striking change in the 14 N and proton coupling constants on going from the radical anion I · Θ to the radical cations I(2H) · ⊕ and I(2 CH 3 ) · ⊕. This change can be rationalized in terms of the HMO model of the pyrene π‐system. A reversal in the energy sequence of the lowest antibonding orbitals is predicted upon an increase in the absolute value of the Coulomb integral for the azasubstituted π‐centres, such an increase simulating the enhanced electronegativity of the azanitrogen atoms 2 and 7 on protonation.