title: Through-bond interactions in the diradical intermediates formed in the rearrangements of bicyclo[n.m.0]alkatetraenes.
abstract: The intermediates and transition structures in the degenerate thermal rearrangements of bicyclo[4.4.0]deca-2,4,7,9-tetraene (1c), bicyclo[5.5.0]dodeca-2,4,8,10-tetraene (11b), and bicyclo[5.4.0]undeca-2,4,8,10-tetraene (14) have been located by (U)B3LYP/6-31G(d) calculations. The singlet-triplet energy differences (ΔE(ST)) in the diradical intermediates (tricyclo[4.4.0.0(2,7)]deca-3,8-dien-5,10-diyl (2c), tricyclo[5.5.0.0(5,11)]dodeca-2,8-dien-4,10-diyl (12b), and tricyclo[5.4.0.0(5,11)]undeca-2,8-dien-4,10-diyl (15)) have been computed, using both UB3LYP and (6/6)CASPT2 calculations. ΔE(ST) in 2c, in which a four-membered ring is anti-bridged by two allylic radicals, is computed to be larger by a factor of 5 than ΔE(ST) in 15, in which the anti-bridged ring is five-membered, and by a factor of 10 than that in 12b, in which the anti-bridged ring is six-membered. The reasons for the much larger interaction between two allylic radicals through the bonds of the four-membered ring in 2c than through the bonds of the five-membered ring in 15 or the six-membered ring in 12b are discussed, and the consequences of the large, through-bond stabilization of the singlet state of 2c are described.
authors.affiliation: Department of Chemistry and Center for Advanced Scientific Computing and Modeling, University of North Texas, 1155 Union Circle No. 305070, Denton, Texas 76203-5017, USA.
authors.forename: Charity Flener
authors.initials: CF
authors.lastname: Lovitt
authors.forename: Hao
authors.initials: H
authors.lastname: Dong
authors.forename: David A
authors.initials: DA
authors.lastname: Hrovat
authors.forename: Rolf
authors.initials: R
authors.lastname: Gleiter
authors.forename: Weston Thatcher
authors.initials: WT
authors.lastname: Borden