Exploring the structure and energetics of the diradical pyrazine isomers, 2,3-didehydropyrazine (ortho), 2,5-didehydropyrazine (para) and 2,6-didehydropyrazine (meta), is an important step to improving antitumor drug effectiveness and understanding certain bond-making and breaking processes in organic syntheses. The isomers were characterized using multireference quantum chemical methods. The lowest lying singlet and triplet states were investigated because the ordering of these states indicates the stability of the diradical. Adiabatic and vertical gaps between the lowest lying singlet and triplet states were compared. It is found that the para(2,5) isomer is the most promising as an antitumor warhead. The latest advancements in the development of multi-configuration pair-density functional theory, MC-PDFT, including analytical gradients for state-averaged wave functions will also be presented.

Diradical pyrazine isomer characterization and analytical gradients for state-averaged MC-PDFT

2019 Spring National Meeting

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