A computational study of the electron affinities of substituted Cope rearrangement transition states†

Abstract

The structures and properties of the negative ions of the transition states of the Cope rearrangement of hexa-1,5-diene and 2,5-dicyanohexa-1,5-diene and the negative ion of cyclohexanedione are examined at the Becke3LYP/6-31+G* level of theory. The negative ion of the hydrocarbon cyclohexane-1,4-diyl is calculated to be unstable with respect to electron detachment and with respect to ring opening. Addition of two cyano substituents results in an ion that is stable with respect to both electron detachment and with respect to ring opening, such that the Cope rearrangement has an inverted potential energy surface for the negative ion. The negative ion of cyclohexanedione is calculated to be stable with respect to ring-opening, but unstable with respect to electron detachment in the chair conformation. The ion in the boat geometry is predicted to be stable with respect to vertical electron detachment, suggesting that bicyclo[4.2.0]octa-2,5-dione will form a stable negative ion in the gas phase.