V. A. Korolev

IR Spectroscopic study of matrix-isolated free allyl radicals and analysis of vibrational spectra and structure of π-allyl organometallic compounds

Conclusions1.By the technique of matrix isolation of products from the vacuum pyrolysis of 1,5-hexadiene-d10, the IR spectrum of the free allyl radical C3D5 has been obtained for the first time.2.On the basis of the IR spectra of the C3H5 and C3D5 radicals, vibrational frequencies of the allyl radical have been calculated, and the bands have been assigned to the normal vibrations.3.A systematic comparison has been made of the vibrational frequencies of the allyl radical and the Π-allyl ligand in the composition of organometallic compounds. It has been established that the frequencies of out-of-plane vibrations ρw(CH2), ρt(CH2), and ρ(CH) are substantially higher for the Π-allyl ligand; the frequencies of vibrations taking place in the plane of the allyl fragment are little different for the two cases. A new assignment has been proposed for a number of frequencies in the spectra of Π-allyl complexes.4.The system of bonds for the allyl radical is characterized by relatively low frequencies of stretching vibrations and the force constant 5. 8 mdyne/Å. The values of νs(CCC) and νas(CCC) show that upon formation of a Π-allyl complex, there is no loosening of the carbon-carbon bonds of the ligand, in contrast to Π-complexes of unsaturated compounds.

Generation and IR spectroscopic study of benzyl radical

The benzyl radical C6H5CH2 has been obtained by gas phase pyrolysis of two different precursors, benzyl bromide and dibenzyl, and studied in an argon matrix at 12 K by IR spectroscopy. Similarly, the deuterosubstituted benzyl radicals, C6H5CD2 and C6D5CH2, have been investigated. The assignment of the IR bands of the benzyl radical and its deuteroanalogs to fundamental modes and a calculation of the valence force field have been performed. The obtained data give evidence of sp2 hybridization of the methylene carbon atom and delocalization of the electron density between the ring and the CH2 group, and are in good agreement with the planar structure of the radical.

Direct IR spectroscopic study of the cyclopentadienyl radical

The products of vacuum pyrolysis of bis(cyclopentadienyl)nickel have been studied by matrix isolation infrared spetroscopy. Three IR bands at 3079, 1383 and 661 cm−1 corresponding to the cyclopentadienyl radical have been observed. A comparison of the IR spectrum of the radical C5H5 with those of the ligand π-C5H5 and free anion−C5H5 has been performed.

Reduction of substituted spiro[cyclopropane-3-(1-pyrazolines)] to spiro[cyclopropane-3-pyrazolidines] and 1-(2-aminoethyl)cyclopropylamine derivatives

Raney nickel-catalyzed hydrogenation of 5-substituted spiro[cyclopropane-3-(1-pyrazoline)]-5-carboxylates occurs with N—N bond cleavage with simultaneous cyclocondensation to give 3-aminopyrrolidin-2-ones containing a spirocyclopropane fragment. The presence of the second ester group in the pyrazoline side chain, in the position ensuring the formation of a five-membered ring results in 6,11-diazadispiro[2.1.4.2]undecane-7,10-dione, the product of double cyclocondensation of the intermediate diamine. Hydrogenation of the aryl-substituted spiro[cyclopropane-3-(1-pyrazolines)] in the presence of acetone affords hexahydrospiro[cyclopropane-4-pyrimidines], which can be converted into the cyclopropane-containing 1,3-diamines in the individual state or as salts.

Infrared spectroscopic investigation of propargyl radicals stabilized in low-temperature argon matrix

Conclusions1.The propargyl radical, obtained by vacuum pyrolysis of propargyl iodide and dipropargly oxalate, has been stabilized in an argon matrix at 12 K and characterized by IR spectroscopy on the basis of 12 of its absorption bands.2.The vibration frequencies of the propargyl radical have been calculated theoretically, the observed bands have been assigned to normal vibrations, and the force field of this radical has been determined.3.The values obtained for the stretching vibration frequencies νC≡C, νC-C, νCH, and νCH2 indicate strengthening of the ordinary carbon-carbon bond and weakening of the triple bond in the propargyl radical as a result of electron density delocalization in the conjugated system of orbitals.

Cascade dimerization of 2-styryl-1,1-cyclopropanedicarboxylate upon treatment with gallium trichloride

Abstract2-Styrylcyclopropane-1,1-dicarboxylate treated with anhydrous gallium trichloride undergoes dimerization with the cyclopropane ring opening and the styryl substituent double bond involvement, leading to the formation of polysubstituted cyclic and bicyclic structures with the predominance of the former or the latter depending on the reaction conditions. Most compounds are formed with very high diastereoselectivity. Thirteen major and minor dimeric structures were isolated and reliably characterized, two of which were found to additionally include a chlorine atom. A rare for the reactions of donor-acceptor cyclopropanes example of the formation of a product with the fused cyclobutane ring was effected at–80 °C. Plausible mechanisms of observed processes were discussed.

Generation of cyclopropanediazonium and its chemical transformations in the presence of phenol

The reaction of phenol with cyclopropanediazonium ion generated in situ from N-cyclopropyl-N-nitrosourea by the action of K2CO3 or Cs2CO3 was studied. The main reaction pathway is diazo coupling of cyclopropanediazonium with phenol to give 4-(cyclopropyldiazenyl)phenol, and only traces of isomeric 2-(cyclopropyldiazenyl)phenol were formed. The reaction was accompanied by partial denitrogenation of the diazonium ion with formation of cyclopropyl and allyl cations which gave rise to a number of by-products. All transformation products were characterized by the 1H and 13C NMR spectra with detailed signal assignment.

IR spectroscopic study of thioacrolein and its photoisomerization to methylthioketene

The molecules of thioacrolein (1) and metylthioketene (3), which are labile under normal conditions, have been studied by the matrix Fourier transform infrared spectroscopy method. Compound1 was obtained by vacuum pyrolysis (1120 K, 10−4 Torr) of diallyl sulfide. The analysis of its IR spectrum shows that1 exists as a mixture ofs-trans ands-cis conformers. UV irradiation (λ > 248 nm) of matrix isolated1 results in a 1,3 hydrogen shift and the formation of3, which is characterized by a strong band of antisymmetric stretching vibrations of the thioketene fragmentvC=C=S at 1777.2 cm−1. The experimental IR bands of molecules1 and3 were assigned to fundamental modes. The relatively low frequencies of the stretching vibrations of the double bonds (vC=C at 1598.0 cm−1 andvC=S at 1071.8 cm−1) and the heightened frequency of the C-C single bond stretching (vC-C 1173.7 cm−1) in the spectrum of1 indicate appreciable delocalization of the electron density in the conjugated π-orbital system.

Direct detection of unstable intermediates from the pyrolysis of allyltrimethylsilane by means of mass spectrometry and matrix IR spectroscopy

Conclusions1.A parallel detection of the primary unstable products of the vacuum pyrolysis of allyltrimethylsilane has been carried out by means of mass spectrometry and matrix IR spectroscopy, and it has been established that dissociation of this compound occurs both into free allyl and trimethylsilyl radicals and simultaneously into propylene and silaethylene.2.The radical SiMe3 is unstable under the conditions of vacuum pyrolysis at temperatures above 700° and decomposes with formation of Ca2H4, C2H4>CH2, and methyl radicals.3.The allyl radical is characterized by the ratio of the intensities of the ions generated during its dissociative ionization and the vibrational frequencies in the matrix IR spectra.

High-vacuum pyrolysis of 1,1,1-trifluoro-2-bromo-2-chloroethane. IR spectrum of 1,1,1-trifluoro-2-chloroethyl radical in an argon matrix

The products of high-vacuum pyrolysis of 1,1,1-trifluoro-2-bromo-2-chloroethane were studied by matrix IR spectroscopy. The decomposition of 1,1,1-trifluoro-2-bromo-2-chloroethane was shown to occur predominantlyvia two directions: to form the 1,1,1-trifluoro-2-chloroethyl radical and trifluoromethylcarbene isomerizing to trifluoroethylene. The CF3CHCl radical has been detected in the matrix for the first time. The bands observed in the IR spectrum were calculated by the quantum-chemical B3LYP/6-311 G(d,p) method and assigned to normal vibrations of the radical.