Synthesis of 2,2,5,5-tetramethyl-3-imidazoline-1-oxyl

Condensation of -(hydroxylamino)-2-methylpropanal with acetone and ammonia afforded 2,2,5,5-tetramethyl-3-imidazoline-1-oxyl, the first member of a series of stable nitroxyl radicals which are derivatives of 3-imidazoline. It was shown that 2,2,5,5-tetramethyl-2, 5-dihydropyrazine-1,4-dioxide can reversibly add two molecules of water or ammonia to the nitrone groups.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 931–933, May, 1993.     

A stable nitroxide - 2,2,5,5-tetramethyl-3-imidazoline-3-oxide-1-oxyl - a reagent for spin labeling via 1,3-dipolar cycloaddition

The paramagnetic heterocyclic aldonitrone, 2,2,5,5-tetra-methyl-3-imidazoline-3-oxide-1-oxyl, reacts with C=C and C=N containing dipolarophiles to yield cycloadducts with radical centres.     

Photochemical degradation of 2,2,5,5-tetramethyl-4-phenyl-3-imidazoline-1-oxyl

The photochemical degradation of 2,2,5,5-tetramethyl-4-phenyl-3-imidazoline-1-oxyl has been studied in solution at room temperature and in glassy matrices at 77 K. Nitrogen(II) oxide is split from the starting radical during the reaction. The quantum yield of the reaction constitutes ～0.2 in a liquid solution at 298 K and ～0.001 in glassy matrices at 77 K. The kinetics of the solid-phase reaction have a stepped character.     

Acyl chlorides of 2,2,5,5-tetramethyl-3-imidazolin-1-oxyl-4-0-acylhydroximic acids

Acylation of nitroenamine derivatives of imidazolidin-1-oxyl with carboxylic acid chlorides leads to 0-acylhydroximic acid chloride derivatives of 3-imidazolin-1-oxyl. The reaction proceeds apparently through a nitrile oxide. It was shown for the 0-benzoyl derivative that reaction of the obtained acyl chlorides with nucleophilic reagents usually gives products of chlorine atom substitution with simultaneous cleavage of the acyl group.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 444–450, February, 1991.     

Synthesis,structure, and magnetic properties of mixed-ligand complexes of manganese and gadolinium hexafluoroacetylacetonates with 4-phenyl-2,2,5,5-tetramethyl-3-imidazoline-3-oxide-1-oxyl nitroxide

Complexes of manganese(II) and gadolinium(III) hexafluoroacetylacetonates with stable nitroxide 4-phenyl-2,2,5,5-tetramethyl-3-imidazoline-3-oxide-1-oxyl (L), Mn(hfac)₂L₂ and Gd(hfac)₃L₂, have been synthesized. The results of an X-ray study of these complexes (Mn(hfac)₂L₂: a=21.762(4), b=9.685(1), c=22.073(3) Å, β=114.94(1)°, space group Cc, Z=4; Gd(hfac)₃L₂: a=22.079(4), b=11.562(2), c=21.302(4) Å, β=112.25(1)°, space group Cc, Z=4) have shown that both compounds have a molecular structure with the paramagnetic ligand coordinated via the oxygen atom of the N-oxide group. According to the results of static magnetic susceptibility measurements, the energies of exchange interactions between unpaired electrons of L and of metal ions are less than 1 cm^?1 in magnitude.     

Crystal and molecular structure of (4-amino-2,2,5,5-tetramethyl-3-imidazoline-1-oxyl) bis(hexafluoroacetylacetonato)copper(II)

Institute of Inorganic Chemistry, Siberian Branch, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 32, No. 3, pp. 92–96, May–June, 1991.     

Crystal Structure of Copper(II) and Cobalt(II) Hexafluoroacetylacetonate Complexes with 2,2,5,5-Tetramethyl-4-phenyl-3-imidazoline-1-oxyl-3-oxide

The crystal structures of the copper(II) and cobalt(II) hexafluoroacetylacetonate complexes with the nitroxide 2,2,5,5-tetramethyl-4-phenyl-3-imidazoline-1-oxyl-3-oxide (PhImOx) Cu(hfac)₂(PhImOx), Co(hfac)₂(PhImOx), and Co(hfac)₂(PhImOx)₂ have been determined. The former two are chain type complexes, whereas the latter has a molecular structure. The coordination polyhedra of the copper and cobalt atoms are tetragonally distorted octahedra. In the two chain type compounds, the octahedra are formed from the hfac anion, nitroxyl, and N-oxide O atoms; in the molecular complex, the O atoms of the NO groups are not coordinated to the metal atoms. In the structure of Cu(hfac)₂(PhImOx), F...F contacts equal to 2.805 have been found.     

Behavior of 1-hydroxy-2,2,5,5-tetramethyl-3-imidazoline-3-oxide and the corresponding nitroxyl radicals in superacid media

The protonation of 1-R-2,2,5,5-tetramethyl-3-imidazoline-3-oxides (R=OH, O) in superacid media was investigated with¹H and¹³C NMR. The hydroxylamino dication forming on protonation can undergo imidazoline ring opening to form an isomeric mixture of diprotonated N-(2-hydroxyimino-1,1-dimethylethyl),,-dimethylnitrones.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2755–2761, December, 1991.     

Crystal structure of bis[2,2,5,5-tetramethyl-3-imidazoline-1-oxyl-4-(1′-propenyl-2′-oxyato)]nickel(II), Ni(C10H16N2O2)2

Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences. Translated from Zhurnal Strukturnoi Khimii, Vol. 33, No. 2, pp. 112–117, March–April, 1992.     

Modulation effects in the electron spin echo of biradical systems

The results of a theoretical and experimental investigation of the modulation effects in the electron spin echo of biradical systems are presented. SO ₄ ^– radicals stabilized as pairs in UV-irradiated potassium persulfate and frozen solutions of the stable N,N-[bis-(, -diphenylpicrylhydrazyl)--picryl-3]-piperazine biradical (A) were chosen as models. The modulation effects in the ESE of SO ₄ ^– radicals in potassium persulfate are shown to be caused by a dipole-dipole interaction between the radicals. The results of the study of the ESE of the A-biradicals leads to the assumption that the observed modulation effects are caused by an exchange interaction between unpaired electrons.The authors are grateful to V. E. Khmelinskii, M. D. Shchirov, A. M. Raitsimring, and R. I. Zusman for their help in carrying out the experiments. The authors are especially grateful to R. O. Matevosyan for kindly supplying biradical A.     

Structure and Magnetic Properties of the Stable Nitroxide 2-Cyano-4,4,5,5-tetramethyl-3-oxide-2-imidazoline-1-oxyl

Crystal and molecular structure of the nitroxide 2-cyano-4,4,5,5-tetramethyl-3-oxide-2-imidazoline-1-oxyl was studied. The nontrivial features of the structure are coplanarity of all atoms of the 2-imidazoline heterocycle and the nitrile group bonded to it and short intermolecular contacts between the nitroxyl O atoms and the C atoms in the 2 position of the heterocycles of the neighboring molecules, actually forming layers in the crystal structure. These data agree with the results of magnetic studies, which are well approximated by the two-dimensional model, which is a rare occurrence for organic magnets.     

Reactions of heterocyclic paramagnetic aldonitrone, 2,2,5,5-tetramethyl-3-imidazoline-1-oxyl 3-oxide, with alkynes

The reactions of heterocyclic paramagnetic aldonitrone,viz., 2,2,5,5-tetramethyl-3-imidazoline-1-oxyl 3-oxide, with mono- and disubstituted alkynes afford unstable isoxazoline derivatives. The reactions with monosubstituted alkynes yield predominantly 5-substituted regioisomers. The resulting isoxazoline derivatives are readily (and often spontaneously) converted into enaminoketones,viz, imidazolidine-1-oxyl derivatives. In the presence of tolan, the title paramagnetic aldonitrone gives a dimer in which one imidazoline ring undergoes profound transformation. The structure of the resulting dimer was established by X-ray diffraction analysis. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 112–117, January, 2000.     

Reactions of heterocyclic paramagnetic aldonitrone, 2,2,5,5-tetramethyl-3-imidazoline-1-oxyl 3-oxide, with alkynes

The reactions of heterocyclic paramagnetic aldonitrone,viz., 2,2,5,5-tetramethyl-3-imidazoline-1-oxyl 3-oxide, with mono- and disubstituted alkynes afford unstable isoxazoline derivatives. The reactions with monosubstituted alkynes yield predominantly 5-substituted regioisomers. The resulting isoxazoline derivatives are readily (and often spontaneously) converted into enaminoketones,viz, imidazolidine-1-oxyl derivatives. In the presence of tolan, the title paramagnetic aldonitrone gives a dimer in which one imidazoline ring undergoes profound transformation. The structure of the resulting dimer was established by X-ray diffraction analysis. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 112–117, January, 2000.     

Modulation effects in A 2+1 electron spin echo pulse sequence

Conclusions Theoretical and experimental studies have been made on the ME trends in 2+1 sequences. The method has advantages over previous ones in having less dead time (not more than 50–100 nsec, as against not less than 300–400 nsec in the two-pulse case) and the absence of relaxation decay and combination frequencies.On the other hand, the method requires more exact information on the pulse lengths and amplitudes and exact shape data.We consider the method most promising for systems showing rapid fall in modulation amplitude, i.e., with nuclei close to the electron spin's.We are indebted to A. Yu. Pusep, S. A. Dikanov, and Yu. D. Tsvetkov for an extremely useful discussion.Institute of Chemical Kinetics and Combustion, Siberian Branch, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 29, No. 1, pp. 73–80, January–February, 1988.     

Molecular structure of 1-nitroso-4-phenyl-2,2,5,5-tetramethyl-3-imidazoline-3-oxide,the nearest structural analogue of the corresponding nitroxyl radical

Novosibirsk Institute of Organic Chemistry, Russian Academy of Sciences, Northern Division Translated from Zhurnal Strkturnoi Khimii, Vol. 33, No. 6, pp. 201–203, November–December, 1992.