Stabilization Energies of Extensively Conjugated Propargylic Radicals

G3(MP2) and other model chemistry calculations indicate that stabilization energies of extensively conjugated allylic radicals H2(C=C)nCH2*, n = 1-4, increase monotonically as the number of repeating C=C units increase. In contrast, stabilization energies of the analogous propargylic radicals, H(C[triple bond]C)nCH2*, decrease beyond n = 2. Breaking up the number of contiguous conjugated C[triple bond]C units in conjugation with the odd electron enhances rather than diminishes stability. These results complement previous findings of significant differences in the stabilization of conjugated ground-state polyenes vs polyynes.