ESR. Spectra of the Radical Anions of Cycloalkylbenzenes

Abstract

(21 XI 70)Sznr~mnary. Ridical anions of five cycloalkylbenzencs (alkyl = propyl. butyl, pentyl, hcxyl, or hcptylj have been studied by ESR. spectroscopy a t -90°C. I n the case of cyclopropylbenzene, no reliable cxperimcntal data could he obtained, because of the instability of its radical anion. The spectra. of the radical anions of the four higher homologues have been analysed by means of a computer program. The assignment of the coupling constants to the a-protons in the pova position o f the benzene ring and to thc cycloalkyl /J-protons has been based on the spectra of spccifically deutcrated deriv.itives.The experimental data of thc radical anion of cycloalkylbenzenes have been coinpared with those of the radical anions of five alkylbcnzcnes (alkyl = methyl, ethyl, n-propyl, isopropyl, or t-butyl), the spectra of the latter being reexamined at -90°C. I n the cycloalkyl series the degeneracy o f the two benzene-type lowest antibonding orbitals is thc morc effectively removed thc largcr the substituent, whereas the reverse relation holds for the non-cyclic series. Thc prefcrrcd conformation of the substituents is that in which the alkyl or cycloalkyl ,?-proton is near t o the nodal planc of the benzene n-system, and this preference is acccntuated with the increasing size of the substituent group.Because of the near-degeneracy of orbitals in monosubstituted alkyl derivatives of benzene, the corresponding radical ions are of special interest for theoretical chemistry (see e.g. In tlie present paper we communicate tlie ESR. results for the radical anions of five cycloalkylbenzenes, VIQ to XO. These results partially disagree with those reported previously. Whereas the radical anions VIIE) to Xe were sufficiently stable for ESK. studies at -9O"C, the instability of VI@ precluded the observation of intense and reproducible spectra.The investigations reported in the present paper were restricted to a single temperature cited above. Since tlie coupling constants of tlie protons in the radical l)

Persistance of the Cyclopnane Radical Anions and its Relation to Structure

“…The previous identification of the secondary product from 3 (1,3,5) as 8Q [4] has been confirmed in the present work by synthesis of 8 [9] and reduction of this compound to its radical anion. The spectra resulting therefrom are the same as those observed on starting from 3(1, 3,5).…”

“…tent to be characterized by their hyperfine data, those of the remaining five cyclophanes undergo a rapid cyclization to the radical anions of4,5,9,10-tetrahydropyrenes. These have been identified as the unsubstituted tetrahydropyrene (from [2.2]metacyclophane and [23] (1,2,3)cyclophane), the 2,7-dimethyl-derivative (from [2,] (1,3,5)-and p4] (1,2,3,5)cyclophanes) and the 1, 8-dimethyl-derivative (from [24] (1,2,3,4)cyclophane). The persistence of the cyclophane radical anions seems to depend on the numbers, nmeta and npa,a, of the meta-and para-positions of the bridging ethano groups in the two benzene rings.…”

Dibenzohomopyracylene, a Segment of Methanofullerene C61H2, Its Radical Ions and Dianion

“…and reduction of 2 with potassium metal in 1,2-dimethoxyethane to the anion 2 .À were carried out according to the standard vacuum technique. [14] Dianion 2 2À : Compound 2 (1 mg) was placed at the bottom of an evacuated 5 mm NMR tube connected to a lithium press. Dry perdeuteriotetrahydrofuran was distilled into the tube under vacuum and degassed by repeated freeze-pump cycles.…”

Powerful Oxidizing Properties of a Planar [8]Annulene: Tetrakis(perfluorocyclobuta)cyclooctatetraene and Its Radical Anion

“…Like 1 [13], compound 2 displays two reversible Radical Anions. Reduction of compounds 1 and 2 to their radical anions was carried out with K in 1,2-dimethoxyethane (DME), either by a direct contact with the metallic mirror or indirectly by the method of solvated electrons [18]. For 1, however, mere shaking of the DME solution of the compound with Hg metal was sufficient to produce the highly persistent radical anion 1 .À which survived even in the presence of air.…”