Date: April 18, 2012
Creator: Lineberger, W. Carl & Borden, Weston Thatcher
Description: This article discusses qualitative theory, quantitative calculations, and direct experiments. This Perspective describes research, carried out in the authors' labs over the past forty years, aimed at understanding, predicting, and measuring the singlet-triplet energy differences (∆Est) in diradicals. A theory for qualitatively predicting the ground states of diradicals and the use of Negative Ion Photoelectron Spectroscopy (NIPES) for measuring ∆Est are described. The application of this theory, ab initio calculations, and NIPES to the prediction and measurement of ∆Est in a wide variety of organic diradicals is detailed. Among the diradicals that are discussed in this Perspective are HN, CH3N, PhN, CH2, trimethylenemethane (TMM), oxyallyl (OXA), meta-benzoquinodimethane (MBQDM), meta-benzoquinone (MBQ), tetramethyleneethane (TME), 1,2,4,5-tetramethylenebenzene (TMB), and D8h COT were, in fact, collaborations between the research groups of the authors. These two projects both took advantage of the ability to NIPES to provide information about transition states. Transition-state spectroscopy was used to measure the cabonyl stretching frequency in the singlet state of OXA and to establish that D8h COT violates the strictest version of Hund's rule.
Contributing Partner: UNT College of Arts and Sciences