EPR observation of cathodically-generated radical anions of colchicides and isocolchicides, and a comparison with the radical anions of troponoids. A general rationalization of the spin-density distribution in these systems
| Autor: | Cavazza M., Pinzino C., Pardi L., Nucci L., Pergola F., Pietra F. |
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| Rok vydání: | 2002 |
| Zdroj: | Tetrahedron (Oxf., Print) 58 (2002): 9553–9558. info:cnr-pdr/source/autori:Cavazza M., Pinzino C., Pardi L., Nucci L., Pergola F., Pietra F./titolo:EPR observation of cathodically-generated radical anions of colchicides and isocolchicides, and a comparison with the radical anions of troponoids. A general rationalization of the spin-density distribution in these systems/doi:/rivista:Tetrahedron (Oxf., Print)/anno:2002/pagina_da:9553/pagina_a:9558/intervallo_pagine:9553–9558/volume:58 |
| Popis: | Cathodic reduction of 10-ethylthiocolchicide (2), 9-ethoxyisocolchicide (3), 9-methylthioisocolchicide (4), 9-n-butylthioiso-colchicide (5), and 9-phenylthioisocolchicide (6) at a platinum electrode in DMF under N2 gave the corresponding radical anions for which EPR spectra were recorded. Voltammetric analysis of these compounds revealed a reversible wave at minimum scan rate 0.10.5 V s 2 1 . Hyperfine coupling constants (hfcc) for these radical anionsassigned by spectral simulation and DFT calculations of electron spin densitiesare highest at the position adjacent to the carbonyl group. Decreasingly small hfccs were assigned, in the given order, to the g and b positions with respect to the carbonyl group. This trendwhich is only marginally affected by oxygen, amino, and sulfur substituentscan be qualitatively rationalized on the basis of classical resonance structures. These afford stability to the system in diminishing order for the unpaired electron at the a, g,orb position with respect to the cycloheptatrienone carbonyl group, which corresponds to conjugation of the unpaired electron through three, two, or one CvC bonds, respectively. Similar conclusions apply to a variety of substituted troponoids. |
| Databáze: | OpenAIRE |
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