Form of the dihedral angle dependence of the spin-spin coupling constant JHNNH

Cyclic hydrazides (derivatives of phtalhydrazide,pyrozolidone-3, indazolone, cyclic hydrazide camphoric acid) are studied by the NMR¹H method. The size of the dihedral HNNH angle of several model compounds (pyrozolidone-3, cyclic hydrazide norcamphoric acid) are calculated by the MINDO/3 SSF MO LCAO method. It is shown that in the hydrazides with HNNH dihedral angle 0–70° the magnitude of the HNNH spin-spin interaction constant does not exceed 1 Hz. The form of its dependence on the dihedral angle is determined.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 3, pp. 363–366, 1989.     

A deuterium nuclear quadrupole double resonance study of the ferroelectric phase transition in potassium dihydrogen phosphate

A study has been made of the nuclear quadrupole double resonance (NQDR) spectrum of deuterium in a powdered sample of potassium dihydrogen phosphate, KH₂PO₄ or KDP for short, both as a function of temperature and of percentage deuteration. Double transitions have also been observed and these enable the orientation of the ferroelectric electric field gradient (EFG) tensor to be determined.     

Kinetics of the reaction of C6H5 with HBr

The rate constant for the reaction of phenyl radical with hydrogen bromide has been measured with the cavity-ring-down method at six temperatures between 297 and 523 K. The Arrhenius expression for the H abstraction reaction can be effectively given by: . The values of these parameters are similar to those for the H + HBr reaction, but are in sharp contrast to those for alkyl radical reactions. The gross difference between the alkyl radical reactions and the phenyl and H-atom reactions could be rationalized in terms of the inductive effects of these radicals as measured by Taft's σ* (polar) constants. © 1993 John Wiley & Sons, Inc.     

Radiation-induced crosslinking and grafting of two polyphosphazene elastomers

The radiation-induced crosslinking and grafting of two aryloxy-substituted elastomeric polyphosphazenes have been carried out by both gamma and electron beam irradiation. The classic Charlesby–Pinner [1] plus a simpler approach were used to determine the G(X) values for the crosslinked elastomeric polymers. The apparent G(X) value for the same polymer depended on whether the gamma-ray or the E-beam results were used. The presence of 8.5% repeat units with allylic groups in the side chain increased the G(X) value by an order of magnitude when the irradiation was performed under vacuum with the gamma source. The extent of acrylic acid grafting was also higher for the polymer containing the allylic group. Nearly all the grafted polyphosphazene films were insoluble in THF, a good solvent for the ungrafted samples.     

Synthesis of N-(5-tetrazolyl)amidines from 5-aminotetrazole and nitriles using organoboranes

Conclusions A method has been proposed for the synthesis of N-(5-tetrazolyl)amidines from 5-amino-tetrazole, nitriles, and organoboranes through boron chelate compounds, namely, dialkyl-boryl[N-(5-tetrazolyl)amidinates].Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2622–2624, November, 1987.     

Some electrohydrodynamic effects in fluid dispersions

Under the combined influence of applied shear and electric fields, the macroscopic behavior of suspensions reflects coupling of the two fields which produces stresses at the phase boundaries. These stresses in turn cause motion and/or deformation of the suspended phase. Electrohydrodynamic (EHD) factors which govern these motions and deformations are reviewed in detail. both in a general theoretical context and also in terms of extensive experimental observations. Throughout an attempt has been made to relate the microscopic behaviour (including interactions) of the suspended phase to macroscopically observable or bulk properties of the suspension as a whole.The phenomena reviewed here are important to a large number of colloidal problems of interest to the physical, biological and earth sciences.     

Molecular structures of acetylene derivatives of tin: Part IV. Gas-phase electron-diffraction study of tetraethynyltin,Sn(CCH)4, and triethynyltin iodide,ISn(CCH)3

The geometrical parameters of tetraethynyltin and triethynyltin iodide have been determined by gas-phase electron diffraction. Triethynyltin iodide was present as an admixture in both the tetraethynyltin samples studied. Because the samples differed significantly in percentage of the iodide (17.4 ± 4.0 and 47.1 ± 3.5 mol %, in samples A and B, respectively), it was possible to determine the structures of both molecules to a sufficient degree of accuracy.The r_α, structures were solved by the least-squares treatment of the molecular intensities, using mean amplitudes and shrinkage corrections calculated from the force fields of a number of tin derivatives.The T_d-symmetry model of Sn(CCH)₄ was refined to give the following parameters: Sn-C, 2.068(5); CC, 1.228(8); CH, 1.079(51). The structural parameters for ISn(CCH)₃ (on the basis of the C_3v model with linear Sn-CC-H fragments) are as follows: Sn-I, 2.646(4); Sn-C, 2.062(17); CC, 1.226(6); ∠ISnC 108.0(2.8). (The thermal average bond distances, r_g, are given in Å, and the valence angle, rα, in degrees; the values in paren- theses are three times the standard deviations, 3σ.)The Sn-C bonds in Sn(CCH)₄, and ISn(CCH)₃ are shorter than the corresponding bonds in the monoethynyltin derivatives, Me₃SnCCH and Me₃SnCCSnMe₃. The SnI bond in ISn(CCH)₃ is noticeably shorter than those in stannane iodide and trimethylstannane iodide.     

Conformation and chiroptical properties of mandelic acids

Using CD data (solution, solid state, various temperatures), X-ray data and MO calculations for a number of substituted mandelic acids (phenylglycolic acids) an attempt was made to explain the different results for the relation between sign of the ¹L_b CD band and substitution pattern as described in the literature for various types of aromatic compounds. Moreover the reported sector rule has been reconsidered taking into account the sign and magnitude of the spectroscopic moments. It has been found that in any explanation of the signs of the ¹L_b CD bands of substituted aromatic compounds both the conformational behaviour and the spectroscopic moments should be taken into account.