Portal de Periódicos da CAPES

Substituenteneffekte auf die CC‐Bindungsstärke, 10. Resonanzstabilisierung von Alkylradikalen durch zwei geminale Cyangruppen

1991; Wiley; Volume: 124; Issue: 5 Linguagem: Inglês

10.1002/cber.19911240535

0009-2940

Joachim Pakusch, Hans‐Dieter Beckhaus, Christoph Rüchardt,

Organic Light-Emitting Diodes Research

Effects of Substituents on the Strength of C–C Bonds, 10. – Resonance Stabilization of Alkyl Radicals by Two Geminal Cyano Groups The activation parameters of the homolytic cleavage of the C q – C q bonds of several dialkylated malonodinitriles ( 2 – 5 ) and of 1,1,2,2‐tetracyanoethane ( 7 ) and the heat of dissociation of 6 in solution have been determined. Together with the ground state strain of the radical precursors (obtained from the heats of combustion or EFF calculations) the steric influence on the dissociation process has been determined. The resonance stabilization energy of α,α'‐dicyanoalkyl radicals then calculated was (12.4 ± 0.9) kcal/mol. This result is discussed within the concept of capto‐dative stabilization. The destabilizing interaction of two geminal cyano groups is apparently the same in the ground state of 2 – 7 and the radicals generated from them.