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ESR. Spectra of the Radical Anions of Cycloalkylbenzenes
Author(s) -
Gerson F.,
Moshuk G.,
Schwyzer M.
Publication year - 1971
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19710540141
Subject(s) - chemistry , substituent , alkyl , isopropyl , medicinal chemistry , benzene , alkoxy group , antibonding molecular orbital , crystallography , photochemistry , atomic orbital , organic chemistry , physics , quantum mechanics , electron
Radical anions of five cycloalkylbenzenes (alkyl = propyl, butyl, pentyl, hexyl, or heptyl) have been studied by ESR. spectroscopy at −90°C. In the case of cyclopropylbenzene, no reliable experimental data could be 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 α‐protons in the para position of the benzene ring and to the cycloalkyl ß‐protons has been based on the spectra of specifically deuterated derivatives. The experimental data of the radical anion of cycloalkylbenzenes have been compared with those of the radical anions of five alkylbenzenes (alkyl = methyl, ethyl, n ‐propyl, isopropyl, or t ‐butyl), the spectra of the latter being reexamined at −90°C. In the cycloalkyl series the degeneracy of the two benzene‐type lowest antibonding orbitals is the more effectively removed the larger the substituent, whereas the reverse relation holds for the non‐cyclic series. The preferred conformation of the substituents is that in which the alkyl or cycloalkyl ß‐proton is near to the nodal plane of the benzene π‐system, and this preference is accentuated with the increasing size of the substituent group.