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Electrochemical properties and radical anions of carbocycle‐fluorinated quinoxalines and their substituted derivatives
Author(s) -
Shundrin Leonid A.,
Irtegova Irina G.,
Vasilieva Nadezhda V.,
Avrorov Pavel A.,
Selikhova Natalia Yu.,
Makarov Arkady G.,
Makarov Alexander Yu.,
Slizhov Yuri G.,
Zibarev Andrey V.
Publication year - 2017
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.3667
Subject(s) - chemistry , electron paramagnetic resonance , cyclic voltammetry , quinoxaline , moiety , electrochemistry , density functional theory , medicinal chemistry , crystallography , stereochemistry , computational chemistry , organic chemistry , electrode , physics , nuclear magnetic resonance
Electrochemical reduction (ECR) and oxidation (ECO) of 5,6,7,8‐tetrafluoroquinoxaline ( 1 ) and its derivatives bearing various substituents R (7‐H ( 2 ), 7,8‐H 2 (3 ), 6‐CF 3 ( 4 ), 6‐Cl ( 5 ), 5,7‐Cl 2 ( 6 ), 5‐NH 2 ( 7 ), 6‐OCH 3 ( 8 ), 6,7‐(OCH 3 ) 2 ( 9 ), 6,7,8‐(OCH 3 ) 3 ( 10 ), 5,6,7,8‐(OCH 3 ) 4 ( 11 ), 6‐OCH 3 ,7‐N(CH 3 ) 2 ( 12 ), 6‐N(CH 3 ) 2 ( 13 ), 6,7‐(N(CH 3 ) 2 ) 2 ( 14 ), 5,6,7‐(N(CH 3 ) 2 ) 3 ( 15 ), and 7,8‐ cyclo‐ ( = CF‐CF = CF‐CF=) ( 16 )) in the carbocycle have been studied by cyclic voltammetry in MeCN. For 1 – 4 and 7 – 15 , the first reduction peaks have been found to be 1‐electron and reversible, thus corresponding to the formation of their radical anions (RAs), which are long lived at 295 K except those of 4 – 6 and 15 , 16 . Irreversible hydrodechlorination has been observed for 5 and 6 at the first step of their ECR confirmed by EPR detection of corresponding RAs of 2 and 5,7‐H 2 derivative of 1 ( 17 ) at the next steps. Electrochemically generated RAs of 1 – 3 , 7 – 14 , and 17 have been characterized in MeCN by EPR spectroscopy together with DFT calculations at the (U)B3LYP/6‐31 + G(d) level of theory using PCM to describe the solvent. A noticeable alternation of spin density on the –NCCN– moiety of quinoxaline has been observed for all RAs possessing R‐substitution asymmetry. The comparative electron‐accepting ability of 1 – 15 has been analyzed in terms of their experimental reduction peak potentials and the (U)B3LYP/6‐31 + G(d)‐calculated gas‐phase first adiabatic electron affinities (EAs). The differences in electron transfer solvation energies for 1 – 15 have been evaluated on the basis of ECR peaks' potentials and calculated gas‐phase EAs. The ECO of 1 – 5 and 7 – 14 has been found to be irreversible.