By using 1-methyl-2-formyl-5-Y-substituted pyrroles (1-Ys), 1-methyl-2-formyl-5-Y-substituted pyrrole phenylhydrazones (2-Ys) and 1-methyl-2-formyl-5-Y-substituted pyrrole (4-nitrophenyl)hydrazones (3-Ys) as models for nitrogen-containing heterocyclic aromatic compounds, the K-band ! max values of their UV spectra were measured. Correlation analysis of the # max values by a dual-parameter equation shows that the # max values of these compounds are affected, albeit to different degrees, by both the polar (s x ) and spin-delocalization effects (s Á ) of the substituents. Interestingly, the UV spectra of 3-Ys are mainly affected by the polar effects. The correlation results are in accord with a previous speculation that a higher degree of polarization of the substrate molecule would demand a higher degree of polar assistance from the substituent at the transition states.
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EPR Studies of 1-Methyl-2-substituted-5-pyrrolylcarbonyl Fluorinated Nitroxides and Dual-Parameter Correlation Analysis of Their Hyperfine Splitting Constants.-Freon-113 solutions of H-abstracting bis-per(poly)fluoroalkyl nitroxides and fluorinating nitrosoalkanes, generated simultaneously by the reaction of the corresponding perfluorocarboxylic anhydrides with NaNO 2 , are used to study the generation of new nitroxides (III) and (IV) by EPR. Correlation analysis of their a N values are mainly affected by the polar effect of the 2-substituent, but the spin-delocalization effect also exists.
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