140668-87-7Relevant academic research and scientific papers
Spin Delocalization, Polarization, and London Dispersion Forces Govern the Formation of Diradical Pimers
Ellern, Arkady,Peterson, Joshua P.,Winter, Arthur H.
, p. 5304 - 5313 (2020/04/08)
Some free radicals are stable enough to be isolated, but most are either unstable transient species or exist as metastable species in equilibrium with a dimeric form, usually a spin-paired sigma dimer or a pi dimer (pimer). To gain insight into the different modes of dimerization, we synthesized and evaluated a library of 15 aryl dicyanomethyl radicals in order to probe what structural and molecular parameters lead to σ- versus π-dimerization. We evaluated the divergent dimerization behavior by measuring the strength of each radical association by variableerature electron paramagnetic resonance spectroscopy, determining the mode of dimerization (σ- or π-dimer) by UV-vis spectroscopy and X-ray crystallography, and performing computational analysis. We evaluated three different hypotheses to explain the difference in the dimerization behavior: (1) that the dimerization behavior is dictated by radical spin densities; (2) that it is dictated by radical polarizability; (3) that it is dictated by London dispersion stabilization of the pimer. However, no single parameter model in itself was predictive. Two-parameter models incorporating either the computed degree of spin delocalization or the radical polarizability as well as computed estimates for the attractive London dispersion forces in the π-dimers lead to improved forecasts of σ- vs π-dimerization mode, and suggest that a balance of spin delocalization of the isolated radical as well as attractive forces between the stacked radicals, govern the formation of diradical pimers.
Effect of Substituents on the Bond Strength of Air-Stable Dicyanomethyl Radical Thermochromes
Peterson, Joshua P.,Geraskina, Margarita R.,Zhang, Rui,Winter, Arthur H.
, p. 6497 - 6501 (2017/06/23)
A series of substituted aryl dicyanomethyl radicals were synthesized, and the bonding thermodynamic parameters for self-dimerization were determined from van't Hoff plots obtained from variable-temperature electron paramagnetic resonance and ultraviolet-v
The Benzene Ring as a Dipolarophile: Reactions of Monosubstituted Benzenes with Tetracyanoethylene Oxide
Hoz, A. de la,Pardo, C.,Elguero, J.,Jimeno, M. L.
, p. 99 - 104 (2007/10/02)
The reaction of tetracyanoethylene oxide on one hand and toluene, chlorobenzene, fluorobenzene, anisole, and nitrobenzene, on the other, has been studied.Toluene and the halogenobenzenes yield mixtures of monoadducts, anisole yield p-methoxyphenylmalononitrile and its dimer and nitrobenzene does not react.These results are discussed with the help of a qualitative orbital model. 1H-NMR analysis of some monoadducts has been carried out.Keywords: Benzene derivatives; Tetracyanoethylene oxide; 1,3-Dipolar cycloaddition.
