We study a soliton-like distortion ina quasi-one-dimensional conjugated carbon chain with a single side radical, which contains an unpaired electron, by taking into account the electron-phonon interaction, an extended Hubbard term due to on-site electron-electron interactions and intersite e-e interactions, and the ferromagnetic correlation between itinerant pi-electrons and the unpaired radical electron. It is shown that a critical value of hopping integral exists between the side radical and the main chain, at which a transition from a single soliton-like distorted structure to a pair of soliton-like distortions occurs along the main chain. In addition, the spin density at the dangling site is transferred to the main chain due to the hopping interaction between the main chain and the side radical, and the spin density at the side radical is decreased to zero when the hopping integral is larger than the critical value.