Three new seven-membered ring systems with non-closed shell pi-electron complements have been prepared and their syntheses, properties and theoretical importance will be discussed. Cycloheptatrienyl (Tropenyl) Radical (with Gershon Vincow and Frank R. Hunter) The tropenyl radical, C7H7· (I), has been produced by thermal dissociation of ditropenyl (C7H7-C7H7) in molten naphthalene solution at 200-225°C and its electron spin resonance spectrum observed. The spectrum is consistent with a planar regular heptagonal structure for C7H7· having a uniform time-average spin distribution. The isotopic proton-hyperfine splitting constant is a + Ō = 4. 2 ± 0. 1 gauss and, therefore, |Q| = 29. 4 ± 0. 7 for a seven-membered ring. Cycloheptatrienide (Tropenide) Anion (with Mahmoud R. Rifi) Solutions or suspensions of blue-colored potassium tropenide, C7H7-, K+ (II), have been prepared in three ways: (i) cleavage of tropenyl methyl ether in tetrahydrofuran at -20°C by sodium-potassium alloy to give 9. 8% potassium tropenide, identified by carbonation to cycloheptatriene-7-carboxylic acid, and 78% ditropenyl; (ii) sodium-potassium alloy cleavage of 7-triphenylmethylcycloheptatriene under the same conditions to give potassium tropenide (39% cycloheptatriene-7-carboxylic acid), potassium triphenylmethide (9% triphenylacetic acid) and polymers; and (iii) by proton abstraction from cycloheptatriene by potassium benzyl in toluene or cyclohexane suspensions at 25°C to give potassium tropenide (30% or 6. 5% cycloheptatriene-7-carboxylic acid), unreacted potassium benzyl (6. 5% or 0% phenylacetic acid) and much polymer. Alternative work-up of (ii) or (iii) with D2O produces only C7H7D. Potassium tropenide is soluble and stable in tetrahydrofuran at -20°C except for facile proton exchange with it and its solution shows no electron spin resonance signal; it is insoluble in toluene and cyclohexane to give suspensions that are stable at 25°C. Competitive studies with added hydrocarbons in (i) show that the relative acidities are: Ph3C-H + Ō (33) > Ph2CH-H + Ō (35) > C7H7-H + Ō (36)>PhCH2-H + Ō (37), and, consequently, the empirical resonance energy may be estimated as 0. 7-0. 8β greater than cycloheptatriene, or about 20-22 kcal./mole (assuming β = 16. 5 kcal./mole). 8, 8-Diphenylheptafulvene (with Robert B. Medz) Hydride ion abstraction from 7-(or x-)diphenylmethylcycloheptatriene in CH2Cl2 at 25°C by triphenylmethyl tetrafluoroborate gives 52% diphenylmethyltropenium tetrafluoroborate, Proton abstraction from this salt by an equivalent amount of trimethylamine in CHCl3 at 25°C rapidly gave 97. 5% trimethylammonium tetrafluoroborate and 96. 3% 8, 8-diphenylheptafulvene (III) as red-brown sublimable needles, m.p. 59-60°, stable under nitrogen but reacts readily with atmospheric oxygen; λmax (hexane) 335 mμ (1. 11 à 104) and 240 mμ (1. 36 à 104), λmin 283 mμ (4. 48 à 103) tailing through visible region. Its n.m.r. spectrum in CCl4 by showing peaks at 2. 86Ï for phenyl protons and at 3. 78-4. 74Ï for heptafulvene protons indicates limited ring current and little cyclic pi-electron delocalization.