Characteristic frequencies in the infrared spectra of pyrazolines

Pyrazolines are characterized by valence vibrations at the following frequencies: C=N (1580–1627 cm^–1), H-C³=N (3040–3063 cm^–1), H-N (3270–3305 cm^–1) and CH₃-N (2780–2805 cm^–1). Lowering of the frequencies of the valence vibrations of C=N in pyrazolines, when compared with the magnitudes characteristic of alkyledene amines and oximes, is regarded as a consequence of coupling with the unshared electron pair of the neighboring nitrogen atom. By means of the IR spectra, it is possible to determine the position of the double bonds in the pyrazoline ring, to distinguish between pyrazolines substituted and nonsubstituted in positions 1 and 3, and to establish the presence of geminate (twin) methyl groups and methyl groups in position 1.     

Preparation of the simplest Δ1-pyrazolines by isomerization of Δ2-pyrazolines

²-Pyrazolines that do not have substituants in the 1- and 3-positions are not capable of isomerization to 3-substituted pyrazolines and can be converted to ¹-pyrazolines by slow distillation in the presence of bases. This method, which is completely analogous to the synthesis of azo compounds from alkylhydrazones, gives good results when applied to 4-alkyl- and 5,5-dialkyl-²-pyrazolines and makes it possible to obtain the corresponding ¹-pyrazolines in yields of 40–70%. 4-Ethyl-, 5-methyl-5-ethyl-, and 5,5-diethyl-¹-pyrazolines are described for the first time.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 956–957, July, 1971.     

Isomerization of 5, 5-dimethylpyrazolines. preparation and properties of 5, 5-dimethyl-Δ1-pyrazoline and 3, 4-dimethyl-Δ2-pyrazoline

Slow distillation of 5, 5, -dimethyl-²-pyrazoline isomerizes it to 5, 5-dimethyl-¹-pyrazoline, and heating the latter with hydrazine hydrochloride reconverts it to the ² isomer. This is the first experimental evidence that the ² double bond in a pyrazoline can move to the ¹ position, i. e., in a direction the reverse of that previously known. The 5, 5-dimethyl-¹ -pyrazoline described is the simplest ¹ pyrazoline hitherto isolated.The authors heartily thank A. A. Petrov for making it possible to chart the PMR spectra, and V. B. Lebedev and V. S. Stopskom for obtaining and treating the spectrograms.     

[6,6]‐Open and [6,6]‐Closed Isomers of C70(CF2): Synthesis,Electrochemical and Quantum Chemical Investigation

Novel difluoromethylenated [70]fullerene derivatives, C₇₀(CF₂)_n (n=1–3), were obtained by the reaction of C₇₀ with sodium difluorochloroacetate. Two major products, isomeric C₇₀(CF₂) mono‐adducts with [6,6]‐open and [6,6]‐closed configurations, were isolated and their homofullerene and methanofullerene structures were reliably determined by a variety of methods that included X‐ray analysis and high‐level spectroscopic techniques. The [6,6]‐open isomer of C₇₀(CF₂) constitutes the first homofullerene example of a non‐hetero [70]fullerene derivative in which functionalisation involves the most reactive bond in the polar region of the cage. Voltammetric estimation of the electron affinity of the C₇₀(CF₂) isomers showed that it is substantially higher for the [6,6]‐open isomer (the 70‐electron π‐conjugated system is retained) than the [6,6]‐closed form, the latter being similar to the electron affinity of pristine C₇₀. In situ ESR spectroelectrochemical investigation of the C₇₀(CF₂) radical anions and DFT calculations of the hyperfine coupling constants provide evidence for the first example of an inter‐conversion between the [6,6]‐closed and [6,6]‐open forms of a cage‐modified fullerene driven by an electrochemical one‐electron transfer. Thus, [6,6]‐closed C₇₀(CF₂) constitutes an interesting example of a redox‐switchable fullerene derivative.     

Synthesis of tris(β,β,γ-oximinoalkyl)amines from aliphatic nitro compounds and methyl vinyl ketone

A general strategy for the assembly of previously unknown tris(β,β,γ-oximinoalkyl)amines from aliphatic nitro compounds and methyl vinyl ketone is described. The strategy involves N,N-bis(siloxy)enamines as key intermediates. The latter are accessible by double silylation of alkylnitro compounds. Nickel(II) and copper(II) complexes of tris(β,β,γ-oximinoalkyl)amines are prepared and structurally characterized.     

Structures of Chlorinated Fullerenes,IPR C96Cl20 and Non‐classical C94Cl28 and C92Cl32: Evidence of the Existence of Three New Isomers of C96

Chlorination of various HPLC fractions of C₉₆ with a mixture of VCl₄ and SbCl₅ at 340–360 °C and single‐crystal X‐ray diffraction study of the products led to the identification of three new IPR isomers of C₉₆. The C₉₆(175) isomer forms a stable chloride, C₉₆(175)Cl₂₀, while chlorides of two other new isomers, C₉₆(114) and C₉₆(80), undergo cage shrinkage yielding C₉₄(NC1)Cl₂₈ and C₉₆(NC2)Cl₃₂ with non‐classical (NC) cages. These two NC chlorides contain, respectively, one and two heptagons flanked by pairs of fused pentagons and are stabilized by chlorine attachment to the emerging pentagon–pentagon junctions. Thus, the number of the experimentally confirmed C₉₆ isomers has reached nine, which corroborates the empirical rule that the C_6n fullerenes exhibit particularly rich isomerism.     

An Easy Synthesis of Monofluorinated Derivatives of Pyrroles from β-Fluoro-β-Nitrostyrenes

The catalyst-free conjugate addition of pyrroles to β-Fluoro-β-nitrostyrenes was investigated. The reaction was found to proceed under solvent-free conditions to form 2-(2-Fluoro-2-nitro-1-arylethyl)-1H-pyrroles. The effectiveness of this approach was demonstrated through the preparation of a series of the target products in a quantitative yield. The kinetics of a conjugate addition of pyrrole was studied in detail to reveal the substituent effect and activation parameters of the reaction. The subsequent base-induced elimination of nitrous acid afforded a series of novel 2-(2-Fluoro-1-arylvinyl)-1H-pyrroles prepared in up to an 85% isolated yield. The two-step sequence herein proposed is an indispensable alternative to a direct reaction with elusive and unstable 1-Fluoroacetylenes.     

Transalkylation of Higher Trifluoromethylated Fullerenes with C70: A Pathway to New Addition Patterns of C70(CF3)8

We report three new isomers of C₇₀(CF₃)₈, structurally related to p⁷mp‐C₇₀(CF₃)₁₀, that are inaccessible by direct trifluoromethylation, but can be easily identified among the products of the transalkylation of higher trifluoromethylfullerenes with C₇₀. The reported compounds are characterized by UV/Vis, 1 D and 2 D COSY ¹⁹F NMR spectroscopy, and DFT calculations. A rather unusual addition pattern is observed in p⁶,i‐C₇₀(CF₃)₈ in which one addend is attached remotely from the others; polarization of the adjacent unsaturated bonds by the addend makes the molecule readily oxidizable.     

Nitraminomethylation of silylated polynitrogen heterocyclic compounds in nonaqueous solutions

Trimethylsilyloxy derivatives of 1,2,4-triazole, 3(5)-nitro-1,2,4-triazole, and tetrazole are inert toward 2-nitro-1-trimethylsilyloxy-2-azapropane, but they react with 1-chloro-2-nitro-2-azapropane to give the corresponding nitraminomethyl derivatives. Silyiated 1,2,4-triazole undergoes bis-nitraminomethylation to give a triazolium salt.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1666–1668, September, 1993.