(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)

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The anion radicals of c/.s-bicyclo[6.1.0]nona-2,4,6-triene (I), rranj-bicyclo[6.1.0]nona-2,4,6-triene (II), and cw4-cyclononatetraene (III) have been prepared and their esr spectra measured. Comparison of the esr spectral data shows that I and III yield a species which is a nonclassical nine -electron, monohomocyclooctatetraene, while II produces an anion radical which is a classical seven -electron hexatrienyl system.Various homoaromatic species such as the trishomocyclopropyl cation (IV),3•4 the monohomotropylium cations (V),3•6 1,3-bishomocyclopentadienide anion (VI),3•6 and bicyclo[3.2.2]nonatrienyl anion (VII)3'7 with delocalized two, six, and eight -electron systems have been reported and discussed.Generally, in the field of electron spin resonance of organic paramagnetic species, attention has been focused on investigations of anionic, cationic, and neutral radicals of classical and systems. Prior to this work,1 the use of electron spin resonance spectroscopy as a tool in observation and investigation of the phenomenon of homoconjugation in odd electron systems had not been reported. The electron spin resonance investigation of the radical anions of certain seven and(1) Portions of this work have been published as communications: