Intramolecular hydrogen bonding and structure of stereoisomeric 20(22)-hydroxy-22(23)-isoxazolinyl steroids

We have used IR spectroscopy and the quantum chemical AM1 method to study stereoisomeric 22(23)-isoxazolinyl steroids with a hydroxyl group at C₂₀ or C₂₂, in order to establish the spectral features that will allow us to identify their stereoisomers. We have carried out a conformational analysis of isoxazolinyl steroid stereoisomers, and we have calculated the populations of their stable conformers. We have assigned the bands in the IR spectra of the stereoisomers in the region of the stretching vibrations of OH groups, and have analyzed the possibility of intramolecular hydrogen bond formation between the OH groups and proton-acceptor centers of the isoxazoline ring. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 2, pp. 145–151, March–April, 2006.     

Stability of a matrix finite-difference scheme for solving the problem of elastic vibrations

The stability of a matrix finite-difference scheme is analyzed. The scheme is based on central differences and is designed for the differential equation governing the vibrations of an elastic system.     

Calculation of Plane Vibration Frequencies of the Porphin Molecule

By the DFT/B3LYP method with a 6-31G^** basis set the frequencies of normal vibrations of porphin and its five derivatives have been calculated. Scaling of the force constants for plane vibrations in independent natural coordinates has been carried out. Symmetry coordinates have been introduced and a force field for plane vibrations of the porphin molecule in independent symmetry coordinates has been obtained. Based on an analysis of special matrices and the potential energy distribution, complete matching of the plane vibration frequencies of porphin and its four isotopomers has been performed.     

Nonlinear Analysis of Experimental Time Series of a Straight Turning Process

We investigate vibrations generated in a straight turning process. Applying correlation functions and the Fourier transform to experimental time series, we have analysed their nature. Particularly, we have identified whipping caused by the non-ideal suspension of the cutting workpiece. Our investigation shows also a large stochastic component of vibrations. It can be the effect of random forcing due to the initial roughness of a cutting surface and/or spontaneous chips breaking.     

Vibrations of Curved and Twisted Blades During Complex Rotation

The influence of the curving and twisting of an elongated blade on its vibrations during complex rotation is studied. It is shown that these geometrical factors may cause additional resonant vibrations__________Translated from Prikladnaya Mekhanika, Vol. 41, No. 4, pp. 126–132, April 2005.     

Ab initio Calculation of Normal Vibrations of Chlorobenzene in the First Singlet Electron-Excitebd State 1 B 2

An analysis of experimental assignments of the frequencies of normal vibrations of chlorobenzene in the first singlet electron-excited state ¹ B ₂ has been performed with the use of two quantum-mechanical prediction methods — the method of frequency shifts and the method of transfer of scaling factors. Based on the data of this analysis, a new assignment of a number of vibration frequencies has been made. Normal vibrations of the chlorobenzene molecule in the excited state have been calculated by the CIS method with a 6-311 + G ^** basic set. An algorithm of autoscaling in dependent natural coordinates has been proposed. The force field of chlorobenzene has been scaled in dependent natural coordinates. It is shown that the scaling factors of benzene in the electron state ¹ B _2u can be used for calculating the frequencies of normal vibrations of chlorobenzene in the first singlet excited state ¹ B ₂.     

IR Spectroscopic Investigation and Conformational Analysis of Unsaturated C<Superscript>20</Superscript> and C<Superscript>22</Superscript> Steroid Alcohols

With the IR-spectroscopy method and the quantum-chemical AM1 method, the Δ²² and Δ²³ steroids containing a hydroxyl group at C²⁰ or C²² have been studied in order to elucidate the mutual arrangement in space of the hydroxyl group and of the double bond in the side chain of the molecules. The conformational analysis of steroid alcohols has been performed and the population of their stable conformers has been calculated. The frequencies of the bands in the IR spectra of alcohols in the region of the stretching vibration of OH groups have been assigned to certain conformers and the possibility of formation of the intramolecular hydrogen bond of the OH groups with the π-electron cloud of C=C bonds has been analyzed. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 3, pp. 317–324, May–June, 2005.     

Circular Sandwich Plates under Local Impulsive Loads

The axisymmetric transverse vibrations of a circular elastic sandwich plate under impulsive surface and linear loads are studied. To describe the kinematics of the asymmetric plate, the hypotheses of broken normal are adopted. The core is a lightweight material. Analytical solutions are obtained using Heaviside functions and Dirac delta-function. The solutions are analyzed numerically     

X-ray structure and vibrational spectroscopy of a cobalt(II) complex prepared with excess of 4-hydroxybenzhydrazide

A new cobalt(II) complex was obtained from CH₃OH/H₂O solution containing CoSO₄ and 4-hydroxybenzhydrazide (4hbah) in 1?:?3 molar ratio. The crystals are composed of polymer chains [Co(4hbah)₂(μ-SO₄)] _n accompanied by lattice H₂O and CH₃OH forming the 3-D network. The CH₃OH molecules are highly disordered. For the assignment of IR and Raman spectra, the O,N-deuterated compound was prepared and DFT calculations were carried out.     

Ground‐State Chemical Reactivity under Vibrational Coupling to the Vacuum Electromagnetic Field

The ground‐state deprotection of a simple alkynylsilane is studied under vibrational strong coupling to the zero‐point fluctuations, or vacuum electromagnetic field, of a resonant IR microfluidic cavity. The reaction rate decreased by a factor of up to 5.5 when the Si?C vibrational stretching modes of the reactant were strongly coupled. The relative change in the reaction rate under strong coupling depends on the Rabi splitting energy. Product analysis by GC‐MS confirmed the kinetic results. Temperature dependence shows that the activation enthalpy and entropy change significantly, suggesting that the transition state is modified from an associative to a dissociative type. These findings show that vibrational strong coupling provides a powerful approach for modifying and controlling chemical landscapes and for understanding reaction mechanisms.