The first observation in an organic medium and DFT calculation of the TMM radical anion generated via a single electron reduction of a methylenecyclopropane

γ-Irradiation of 2,2-diphenyl-1-methylenecyclopropane (3) in a degassed 2-methyltetrahydrofuran glassy matrix at 77 K gave an intense UV/vis absorption band with λab at 496 nm. This result and calculations based on density functional theory for its radical anion 3− and the corresponding trimethylenemethane radical anion (2−) strongly suggest that single electron reduction of 3 followed by ready ring opening affords 2−, whose molecular geometry is largely twisted (θ = 45.5°), and the negative charge and spin are localized mainly in the diphenyl methyl and allyl moieties, respectively.