2 mm ESR data on nitroxyl radicals formed by 3- and 2-imidazoline having alkoxy groups attached to the ? carbon atoms in the radicals

First determination of the spin relaxation properties of a nitronyl nitroxide in solution by electron spin echoes at X-band: A comparison with Tempone

“…For short correlation times, T 2 is largely dominated by spin-rotational relaxation, which depends on (Dg:Dg). This term is larger for nitronyl nitroxides (see Table 2 and [70,71]), and this gives a contribution to relaxation which is faster by a factor of 1.6 for PTIO with respect to Tempone. On the other hand, the secular, pseudosecular and non-secular relaxation terms arising from the modulation of the hyperfine 14 N dipolar interaction are larger for Tempone with respect to PTIO due to the smaller principal values of the hyperfine tensors of the latter radical, see Table 2.…”

Stable free imino and nitronyl nitroxyl radicals of the acetylene series: synthesis, electronic absorption spectra and magnetic resonance parameters

“…The A zz values of about 33 G are typical of imidazoline radicals with isolated N-O groups. 3,10 Lower A zz values for the NN and IN radicals are related to a decreased spin density at nitrogen atoms in more extended systems.…”

“…It is well known that the deviation of g xx components from the g-factor for a free electron can be estimated by the formula 3 where l is the spin-orbital coupling constant for an oxygen atom (» 70 cm -1 for a free atom), r π O is the spin density at the oxygen atom and ∆E nπ* is the energy of the long-wave n-π* transition (Table 1). Even with r π O » 1 and ∆E nπ* » 16500 cm -1 (Table 1), ∆g xx » 4.2×10 -3 ; this value is lower than the experimental value (∆g xx » 8.7×10 -3 ) for NN radicals by a factor of two.…”

“…The magnetic parameters of only one derivative of imidazoline-1oxyl and one imidazoline-3-oxide-1-oxyl were measured. 3 In this study, we examined previously unknown acetylene derivatives of nitroxide radicals from the 2-imidazoline series using electronic absorption spectroscopy and 2 mm band EPR spectroscopy. We found for the first time that the substituent at the 2-position of an imidazoline unit poorly influences the magnetic-resonance parameters of imidazoline-3-oxide-1-oxyl.…”

Interpretation of cw-ESR spectra of p-methyl-thio-phenyl-nitronyl nitroxide in a nematic liquid crystalline phase

“…The electron g tensor was used as calculated, with no further adjustments for both the principal values and the orientation on the molecule; besides, its principal values compare well with those reported for other nitronyl nitroxides. 36,37 Concerning the isotropic hyperfine coupling constants with nitrogen nuclei, just a small adjustment was required in order to get a perfect superposition between the experimental spectra and the calculated ones; a shift DA iso = 0.05 G for both the nuclei with respect to the calculated values was evaluated by fitting the 340 K spectrum. The resulting hyperfine coupling tensors were then kept fixed for all the other temperatures.…”