EPR, ENDOR and TRIPLE resonance characterization of three paramagnetic redox stages of 5-methylene-5H-dibenzo [a,d]cycloheptene

Abstract

Radical anions and radical trianions derived from 5-methylene-5H-dibenzo [a,d]cycloheptene 1, 10-deuterio-5-methylene-5H-dibenzo[a,d] cycloheptene 1d and 5-dideuteriomethylene-5-H-dibenzo[a,d]cycloheptene 1d₂ by reduction with lithium, sodium, potassium and caesium in ethereal solvents have been studied by EPR, ENDOR and TRIPLE resonance spectroscopy. The spin and charge distribution in 1˙^– and 1˙^3– are discussed both in terms of HMO–McLachlan and INDO calculations. The energies of the lowest unoccupied molecular orbital (LUMO) and of the next lowest unoccupied molecular orbital (NLUMO) are influenced differently by the strong interaction of the supercharged radical trianion with the counter-cations. A change in the orbital sequence of LUMO and NLUMO was predicted theoretically for the radical trianion relative to that found for the radical anion, in accordance with the experimental results.

The radical cations 1˙⁺, 1d˙⁺ and 1d₂^˙+ obtained via oxidation by AICI₃ in dichloromethane solution were also studied by EPR, ENDOR and TRIPLE resonance spectroscopy. The experimental results were also interpreted in terms of HMO–McLachlan and INDO methods.