EPR study of bridgehead‐substituted bicyclo [2.2.2]oct‐1‐yl and triptycyl radicals

Gavin T. Binmore, John C. Walton*, William Adcock, Christopher I. Clark, Alexander R. Kristic

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

10 Citations (Scopus)

Abstract

4‐Substituted bicyclo [2.2.2] oct‐1‐yl radicals were generated by bromine atom abstraction from the corresponding 1‐bromobicyclo [2.2.2] octanes and observed in solution by EPR spectroscopy. A tendency towards lower a(Hβ) and a(Hγ) values for inductively electron‐withdrawing substituents such as OMe and F and towards higher values for electron‐releasing groups such as Me3Ge and Me3Sn was observed. For a series of bridgehead radicals, the hfs of β‐hydrogens showed a monotonic increase as the extent of flattening at the bridgehead increased. The EPR data indicated that 4‐substitutents exercised a significant effect at the radical centre, mainly by a through‐bond mechanism. 10‐Substituted triptycl radicals were generated in a similar way but showed no hfs from magnetic nuclei of the substituents. Thus, the triptycyl cage transmitted spin density much less effectively than the bicyclo [2.2.2] octyl cage. Bicyclo [2.2.2] oct‐1‐yl and adamant‐1‐yl radicals added to benzene, tert‐butylbenzene and 1,3‐di‐tert‐butylbenzene to give cyclohexadienyl radicals which were characterized by EPR spectroscopy. Triptycyl radicals and strained bridgehead radicals such as cubyl and bicyclo [1.1.1] pent‐1‐yl gave no detectable cyclohexadienyl radicals under similar conditions. Both bicyclo [2.2.2] oct‐1‐yl and adamant‐1‐yl radicals generated in tert‐butylbenzene showed exclusive meta addition with formation of the corresponding 1‐polycyclo‐3‐tert‐butylcyclohexadienyl radical.

Original languageEnglish
Pages (from-to)S53-S59
JournalMagnetic Resonance in Chemistry
Volume33
Issue number13
DOIs
Publication statusPublished - 1 Jan 1995

Keywords

  • bicyclo[2.2.2]octanes
  • EPR
  • radical addition
  • triptycyl compounds

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