Imidazoline nitroxide

Pyrazolylethynylphenylnitroxides 101-104 are quite stable in solid state as well as in solution at ambient temperature. They have typical 2-imidazoline nitroxide EPR spectra. Figures 4 and 5 illustrate the EPR spectra of nitroxides 101 and 102. 

The interaction of imidazoline nitroxide (759) with isocyanates leads to oxadi-azolidines (760), which can be easily transformed into 4/Camino-3-imidazoline-1-oxyls (761) on treatment with nucleophilic reagents (Nu = Nal, NaN3, NH4OH, AcONa, NaH) (Scheme 2.313) (835). 

L. Volodarsky, Imidazolines Nitroxides, CRC Press, Boca Raton, 1988. 

A series of 2-imidazoline nitroxides linked to a pyrazole either directly or through a phenylethynylic bridge show the ESR characteristics of the 2-imidazoline nitroxide moiety. An unexpected strong temperature dependence of magnetic moment for solid 109 was discovered that agrees with the Bleaney-Bowers model for isolated... 

Packing regularities in structures of chelates based on 3-imidazoline nitroxide radical 01KK317. 

Volodarsky, L. B. Imidazoline Nitroxides CRC Press Inc. Boca Raton, FL, 1988. 

The presence of an imine or imine-iV-oxide (nitrone) group in the molecule of imidazoline nitroxides dictates both their stability... 

The presence in the molecule of imidazoline nitroxides of an additional nitrogen atom or of an N-oxide group in combination with functional groups in position 4 of the heterocycle allows com-plexation, chelation, and cyclometalation without participation of the radical center. This made it possible to investigate for the first time the magnetic resonance spectra of multispin systems. 

Thus, the presence in the imidazoline nitroxides of imine or nitrone groups, more basic than the nitroxide group, ensures considerable stability of the nitroxides of the imidazoline series in the presence of acids. 

Numerous derivatives of imidazoline nitroxides with various functional groups have been obtained in the investigations of reactions of 4-alkyl-halide- and 4-alkyl-dihalide-3-imidazoline-3-oxides. The interaction of compounds 7a,b with an equimolar quantity of iV-bromo- and N-chloro-succinimide leads to 4-bromomethyl-, 4-a-bromoethyl-, and 4-a-chloro-ethyl-3-imidazoline-3 oxides (64a,b) (Kutikova and Volodarsky, 1973 Grigor ev and Volodarsky, 1975). With the addition of excess iV-succinimide halide 4-dibromomethyl-, 4-dichloromethyl-, and 4-a,a-dichloroethyl-3-imidazoline-3-oxides (65a,b) are formed (Grigor ev and Volodarsky, 1974 Grigor ev et a/., 1975 Mitasov et ai, 1978). Nitroxides 64 and 65 are reduced by zinc to diamagnetic 1-hydroxy-derivatives 66 and 67. 

Thus, the interaction of a-haloalkylnitrones 64a,b with amines and hydrazine leads to products that contain no iV-oxide oxygen atom. This allows aldehyde and ketone derivatives of 3-imidazoline nitroxide to be synthesized the latter are of interest as spin labels for biological systems (Schlude, 1973). The interaction of the same compounds (64a,b) with nitrogenous nucleophiles, which contain a more electronegative nitrogen atom than that in amines or hydrazine, as well as the interaction with C-, S-, and O-nucleophiles, proceeds with the preservation of the nitrone group and leads to nucleophilic substitution products. Dehydrobromination of 4-bromoalkyl derivatives leads to reactive a,j8-unsaturated nitrones... 

When the properties of the derivatives of carboxylic acids of imidazoline nitroxides were studied the interactions of their amides 31 and 89 with sodium hypobromite were found to proceed in different ways. The interaction of amide 31 with NaOBr gives 4-amino-3-imidazoline-l-oxyl (97), whereas from amide 89 3-hydroxy-2,2,5,5,-tetramethylimidazolidine-... 

Many derivatives of imidazoline nitroxides proved to be capable of chelation without involvement of the radical center. Complexes with ions of transition metals were generated from carboxylic acids 107 and 108... 

The use of imidazoline nitroxides as chelating agents is promising both for identifying the structure of complex compounds and for analytical purposes (see Section 5) since they allow the application of the ESR method... 

The usual NMR spectra of nitroxides have broad lines and are suitable for obtaining structural information only under special conditions. The use of the method of in situ reduction of nitroxides with phenylhydrazine suggested by Lee and Keana (1975) is rather limited because of possible side reactions. Therefore, in the study of imidazoline nitroxides, considerable attention was paid to the vibrational spectroscopy. 

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