13C-NMR spectra of polycyclic compounds and the stereochemistry of unsaturated derivatives of bicyclo[2.2.1]hept(en)ane and related structures

Conclusions Structures of a series of unsaturated bicyclo[2.2.1]hept(en)ane derivatives and related compounds have been established by analysis of their¹³C-NMR spectra, which has also permitted stereochemical assignments of cyclopropane, cyclobutane, and cyclopentene fragments and vinyl groups, relative to the norbornane backbone in each molecule. In the case of 7,7-spirocyclopropane derivatives of norbornane and norbornene, the chemical shift difference for the methylene groups of the cyclopropane fragment proved to be stereochemically informative.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1018–1024, May,1987.     

The reverse shift of the EPR line of paramagnetic centers coupled to species with a fast paramagnetic relaxation

The EPR spectrum of the spin 1/2 paramagnetic centers with a relatively slow relaxation is considered in the case when they are coupled via the Heisenberg exchange interaction to partners which have short times of the longitudinal and transverse paramagnetic relaxation. Under these conditions only the EPR line of paramagnetic centers with a relatively slow relaxation is detectable in experiment. The shape of this line is analyzed by solving numerically kinetic equations for the spin density matrix for simple model systems. Depending on a ratio between the exchange integral and the paramagnetic relaxation rates of partner spins, the EPR line shifts in opposite directions. For moderate relaxation rates, as the relaxation rates decrease, the EPR line shifts toward the gravity center of the total EPR spectrum. In the case of extremely fast relaxation, as the relaxation rates decrease, the reverse shift of the EPR line is expected, the line shifts away from the gravity center of the total EPR spectrum. This type of the non-monotonous line shift was experimentally observed for the monocrystal of [CuNd₂(C₄O₄)₄(H₂O)₁₆] · 2H₂O when relaxation rates were changed by temperature variation.     

Microwave Spectrum of 1,3-Dioxolane in the v=4-8 States of Hindered Pseudorotation

The microwave spectrum of 1,3-dioxolane (C₃H₆O₂) (8 GHz - 53 GHz) has been studied. We identified 247 b type transitions in the v=4, 5, 6, 7, 8 states of excited pseudorotation: rotational transition; vibration-rotation transitions between the v=5 and v=6 states and between the v=7 and v=8 states. Rotational constants, centrifugal distortion constants, and coupling constants between general rotation and hindered pseudorotation have been determined. The intervals _{v v'} between the pseudorotational energy levels have been evaluated: ₅₆=298,618 MHz and ₇₈=201,078 MHz.     

Microwave Spectrum and Hindered Pseudorotation of Tetrahydrofuran

The microwave spectrum of the tetrahydrofuran (C₄H₈O) molecule in the ground state and eight excited states of hindered pseudorotation has been studied. A strong perturbation of rotational spectra has been found for three pairs of pseudorotational states, which is due to the vibrational-rotational interaction. To analyze the nonrigid spectra of these states we used the double resonance technique. Two hundred and sixty nine rotational and vibrational-rotational transitions corresponding to the _a and _c components of the dipole moment have been identified. The rotational constants have been determined along with the quartic constants of centrifugal distortion and the spectroscopic parameters of the interaction between the overall rotation and hindered pseudorotation. The splittings of three pairs of quasidegenerate vibrational levels have been calculated: ₀₁ = 21,308.17 MHz, ₂₃ = 61,205.28 MHz, ₅₆ = 68,183 MHz. The potential function of hindered pseudorotation V()=- 7.84(1-cos2)/2+36.10(1-cos4)/2 (cm^–1) was found from the splittings. It is concluded that the molecule has a twisted conformation (C₂ symmetry) in the states =0 and =1 of hindered pseudorotation and a bent conformation (C_s symmetry) in the states = 2 and = 3. The component of the dipole moment of the transition ‹ = 2 |_c | = 3› = 0.57± 0.01D was determined from the Stark effect of the rotational transitions in the = 2, = 3 states.     

ESR study of complexes of chromium(V) with O-, S-, and Se-containing ligands

Journal of Structural Chemistry -     

EPR of glycol-stibine complex of Cr(V)

Conclusions A new complex of Cr(V) with an antimony-containing ligand was obtained and studied by the EPR method. The additional hyperfine structure from the¹²¹Sb and¹²³Sb isotopes was observed for the first time in solutions of complexes of the transition metals.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 731–732, March, 1974.     

EPR of Gd3+ in single crystal colquiriite and analysis of the spin Hamiltonian tensorsB 4 andB 6

In single crystal colquiriite LiCaAlF₆ doped with Gd³⁺ ions two EPR spectra of the Gd³⁺ ions with the Laue site-symmetry groups C_i and C_3i were observed. The spectrum angular dependence for trigonal Gd³⁺ centre was investigated in detail and corresponding spin Hamiltonian parameters were fitted. From analysis of the spin Hamiltonian tensorsB ₄ andB ₆ it was established that Gd³⁺ with the Laue group C_3i substitutes at Ca²⁺ site with the excess charge compensation by an ion located along the threefold axis from this site. The transformation formulas for a sixth-rank irreducible Hermitian tensor under coordinate rotation are tabulated in an explicit form. By using the EPR data for Gd³⁺ substituted in a variety of host crystals, the fourth-rank and sixth-rank tensors of Gd³⁺ spin Hamiltonians were tabulated and correlated with structures of the coordination polyhedra at substitution sites. The results suppose a predominance of quadratic crystal field contributions into the spin Hamiltonian tensorB ₄ of Gd³⁺.     

Microwave spectrum of preparation of tetrahydro-selenophene-αD4. Structure of ring of molecule and α-methylene groups

Physics Branch, Bashkirian Scientific Center, Ural Branch, Russian Academy of Sciences, Translated from Zhurnal Strukturnoi Khimii, Vol. 33, No. 2, pp. 48—53, March–April, 1992