@article{shultz_boal_lee_farmer_1999, title={Structure-property relationships in trimethylenemethane-type biradicals. 2. Synthesis and EPR spectral characterization of dinitroxide biradicals}, volume={64}, ISSN={["0022-3263"]}, DOI={10.1021/jo990061j}, abstractNote={Several trimethylenemethane-type (TMM-type) dinitroxide biradicals have been prepared that differ in tert-butylaminoxylphenyl ring torsion angles by virtue of different steric demands of their “spin-protecting groups”. In addition, the synthesis of a TMM-type dinitroxide having a planar π-system is reported. The synthetic route employed for the planar TMM-type biradical is general and should therefore expand the utility of TMM-type biradicals that are susceptible to bond torsions that attenuate exchange coupling. The compounds presented are designed to be effective to map out J-coupling/conformation space in TMM-type biradicals. EPR spectroscopic parameters (hfcc and D-values) were compared to determine if their values reflected differences in conformation in the series of biradicals. Interestingly, neither N- nor H-hfcc varied within our series of biradicals/monoradicals in a regular fashion, indicating that there is no apparent relationship between N- or H-hfcc and conformation (as judged by molecular mechanics calculations). However, D-values, estimated from relative intensities of Δms = 1 and Δms = 2 transitions, are consistent with a varied degree of delocalization in the dinitroxides: smaller D-values for biradicals having smaller aryl torsions (and greater delocalization), and larger D-values for dinitroxides having greater aryl torsions (and less delocalization). All the biradicals studied, except 5••, exhibited linear Curie plots. The linear Curie plots are consistent with both triplet ground-states and singlet−triplet degeneracies. Interestingly, dinitroxide 6•• exhibited a linear Curie plot, despite the lack of a π-coupling fragment. Biradical 5••, however, is a ground-state singlet species with the triplet lying about 140 cal/mol above the singlet.}, number={12}, journal={JOURNAL OF ORGANIC CHEMISTRY}, author={Shultz, DA and Boal, AK and Lee, H and Farmer, GT}, year={1999}, month={Jun}, pages={4386–4396} }
 @article{shultz_boal_farmer_1998, title={Synthesis of bis(semiquinone)s and their electrochemical and electron paramagnetic resonance spectral characterization}, volume={63}, ISSN={["0022-3263"]}, DOI={10.1021/jo981597s}, abstractNote={The syntheses of three new bis(semiquinone)s (2••2-, 3••2-, and 5••2-) linked through carbon−carbon double bonds in a geminal fashion (2••2- and 3••2-), and through an sp3 carbon (5••2-), are presented, as well as the results of variable-temperature EPR (VT-EPR) spectroscopy on these biradicals and two previously reported bis(semiquinone)s, 1••2- and 4••2-. We suggest that the potential difference in redox couples associated with a biradical is useful for qualitatively assessing changes in the exchange parameter within an isostructural series. The zero-field-splitting parameters for 1••2-−5••2- are consistent with their electronic structures: biradicals 1••2-−3••2- which have conjugating groups attached to the semiquinone rings have D-values less than 5••2-, a bis(semiquinone) that lacks such a conjugating group. Also, the D-value of 3••2- is significantly less than those of 1••2- and 2••2-, in agreement with larger interelectron separation in 3••2-, a biradical with quinone-methide π-system delocalization. Changes in counterion Lewis acidity are not manifested in the D-values of the biradical dianion 4••2-. The EPR spectrum of biradical 5••2- is consistent with the existence of at least two rotamers having different zero-field-splitting parameters. Biradicals 1••2-−4••2- gave linear Curie plots, consistent with J > 0 (ferromagnetic coupling) or J = 0. The temperature-dependent intensity of EPR signals of 5••2- are characteristic of antiferromagnetic coupling. Best fit results give J = −114 ± 6 cal/mol for the |D/hc| = 0.01309 cm-1 rotamer of 5••2-, and J = −76 ± 3 cal/mol for the |D/hc| = 0.01026 cm-1 rotamer of 5••2-.}, number={25}, journal={JOURNAL OF ORGANIC CHEMISTRY}, author={Shultz, DA and Boal, AK and Farmer, GT}, year={1998}, month={Dec}, pages={9462–9469} }
 @article{shultz_boal_driscoll_farmer_kitchin_miller_tew_1997, title={Preparation of paramagnetic ligands for coordination complexes and networks with interesting magnetic properties}, volume={305}, DOI={10.1080/10587259708045067}, abstractNote={Abstract We hypothesize that paramagnetic, multidentate, chelating ligands can be used to create molecular magnetic materials with high ordering temperatures. The ligands proposed for such materials are di-, tri-, and oligosemiquinone molecules. This paper will discuss the synthesis and characterization of these semiquinone ligands.}, number={1997}, journal={Molecular Crystals and Liquid Crystals Science and Technology. Section A, Molecular Crystals and Liquid Crystals}, author={Shultz, David and Boal, A. K. and Driscoll, D. J. and Farmer, G. T. and Kitchin, J. R. and Miller, D. B. and Tew, G. N.}, year={1997}, pages={303} }
 @article{shultz_boal_farmer_1997, title={The biradical, bis(3,5-di-tert-butyl-4-phenoxyl)methyleneadamantane, exhibits matrix-dependent EPR spectra suggesting rotamer bistability with differential exchange coupling}, volume={119}, ISSN={["0002-7863"]}, DOI={10.1021/ja964330o}, number={16}, journal={JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, author={Shultz, DA and Boal, AK and Farmer, GT}, year={1997}, month={Apr}, pages={3846–3847} }