title: DFT calculations on the effects of para substituents on the energy differences between singlet and triplet states of 2,2-difluoro-1,3-diphenylcyclopentane-1,3-diyls.
abstract: UB3LYP/6-31g* calculations have been performed on a series of para-substituted 2,2-difluoro-1,3-diphenylcyclopentane-1,3-diyls (4). The singlet is computed to be the ground state for each of the diradicals, regardless of the nature of the para substituents, which range from strongly pi-electron-donating (amino) to strongly pi-electron-withdrawing (nitro). In the symmetrically para-disubstituted diradicals, the size of the singlet-triplet energy gap (Delta E(ST)) increases with the pi-electron-donating ability of the substituents, but in the unsymmetrically substituted diradicals, large values of Delta E(ST) are calculated even when one of the substituents is a pi electron acceptor. The origins of the competitive and cooperative substituent effects, predicted for diradical 4, are discussed in light of the calculated effects of the same substituents on the singlet and triplet states of diradical 6, which lacks the geminal fluorines at C-2 that are present in 4.
authors.affiliation: Department of Chemistry and Biochemistry, Seattle Pacific University, Seattle, Washington 98119-1997, USA. daisyz@spu.edu
authors.forename: Daisy Y
authors.initials: DY
authors.lastname: Zhang
authors.forename: David A
authors.initials: DA
authors.lastname: Hrovat
authors.forename: Manabu
authors.initials: M
authors.lastname: Abe
authors.forename: Weston Thatcher
authors.initials: WT
authors.lastname: Borden