Spin‐spin Coupling Between the Biradical Moieties in Aromatic Tetraradicals Increases Their Reactivity

The reactivity of a carbon-centered σ,σ,σ,σ-type singlet tetraradical containing two meta-benzyne moieties, the 2,4,5,7-tetradehydroquinolinium cation, was examined in gas phase toward dimethyl disulfide, cyclohexane and allyl iodide. major reactions were thiomethyl radical abstraction, H atom abstraction respectively. this found to be greater than that relevant biradicals. individual meta-benzynes has been previously controlled by their (calculated) distortion energies (ΔE2.30) singlet-triplet spittings (ΔES-T) as well electron affinities (EA2.30) at TS geometry for hydrogen reactions. addition another moiety generate above does not change EA2.30 only slightly lowers ΔES-T both moieties. However, ΔE2.30 is significantly decreased which explains higher tetraradical. A similar finding made an isomeric tetraradical, 2,4,6,8-tetradehydroquinolinium also contains decrease rationalized stabilizing coupling between one site each tetraradicals. Interestingly, more reactive tetraradicals different: pyridine ring (2,4−) 2,4,5,7-tetraradical while benzene (6,8−) 2,4,6,8-tetraradical. This difference uniquely small value 6,8-moiety 2,4,6,8-tetraradical, makes (and tetraradical) unusually reactive. On other hand, values moieties are differ from other. 2,4-moiety partially rationalizes when compared 5,7-moiety