ESR Investigation of Chemical Exchange in Geminally Diphosphorylated Linear Nitroxide Radicals

Antal Rockenbauer (1) , Gilles Olive (2) , Xavier Rozanska (3) , Alain Jacques (4) , Didier Gigmes (5) , François Le Moigne (5) , Daniel Peeters (4) , Anton German (2) , Paul Tordo (5)

1 Chemical Research Center
2 SPC - Department of Polymer Chemistry and Coatings Technology
3 Schuit Institute of Catalysis, Laboratory of Inorganic Chemistry and Catalysis
4 LCS - Laboratoire de Chimie Structurale
5 CBRL - Chimie, biologie et radicaux libres - UMR 6517

For geminally diphosphorylated linear nitroxide radicals, a marked line width alternation (LWA) can be observed. The LWA appears irrespectively whether the investigated radicals R''N(O.)C(P(O)(OEt)2)2R' contain any chiral group or not. If R"=tertio-butyl and R'=H, the small b-hydrogen coupling indicates a completely blocked rotation around the N-C s-bond and the LWA can be assigned to a chemical exchange between conformations in which the phosphoryl groups have a symmetric and a non-symmetric geometry. The conformational change is accompanied with the deformation of the CP2 bonding angle and the rate of exchange is slowed down in pentane for which the solvent molecules can be trapped by the chelating phosphoryl groups. If R"=benzyl, both the proton hyperfine lines of the CH2 group and the phosphorus lines of the CP2 group produce a LWA ; two coalescences can be observed. In the case of a chiral R" group (R"=secondary butyl, R'=methyl) a tentative four-site model can explain the highly complex LWA.

Domaines: Chimie théorique et/ou physique

Antal Rockenbauer, Gilles Olive, Xavier Rozanska, Alain Jacques, Didier Gigmes, et al.. ESR Investigation of Chemical Exchange in Geminally Diphosphorylated Linear Nitroxide Radicals. Journal of Physical Chemistry A, 2004, 108 (25), pp.5484-5489. ⟨hal-00662572⟩