L. M. Sinegovskaya

Vibrational spectrum and molecular structure of methoxyallene

Abstract Infrared and Raman spectra of methoxyallene and its deuteroderivative CD3OCHCCH2 were analysed on the basis of a scaled ab initio force field (4-21G basis set). Scaling factors were transfered from calculations of allene and dimethyl ether molecules in the same basis set. The ab initio force field scaled in this way provides a good agreement of calculated frequencies with experimental ones. Infrared intensities were calculated and compared with experiment. Contrary to vinyl group CH2 stretching vibration intensities, the intensity of νsCH2 of allenyl group is higher than that of νasCH2. This relation is reproduced by ab initio intensities. Both experimental spectra and ab initio calculations show that the local asymmetry of CH3 group in methoxyallene is the same as in methoxyethene.

IR spectral and dipole moment studies of the conformational isomerism of vinyl sulfides

1. Alterations in the conformations and the conformational ratios of the vinyl sulfides are reflected by changes in the absorption band intensities at 650–750 cm−1 (υC-S-C) and 850–900 cm−1 (νC-S-C) and the values of the dipole moments. 2. Increasing the branching in the substituent decreases the proportion of the vinyl sulfide in the cis rotamer form.

Investigation of electronic structure of allenyl ethers by means of photoelectron and UV spectroscopy

A study of the photoelectron spectra of alkyl allenyl ethers has demonstrated their similarity to spectra of alkyl vinyl ethers, with the exception of a band in the 10.0–10.3 eV interval due to ionization of the π-orbital of the allenyl fragment Cα=Cγ. According to data obtained by photoelectron spectroscopy and MNDO quantum-chemical calculations, alkyl allenyl ethers with straightchain substituents exist primarily in the s-cis conformation. The stable conformation of allenyl tert-butyl ether is the s-trans form. The long-wave absorption bands in the UV spectra of alkyl allenyl ethers at 255–275 and 208–213 nm are assigned to electronic transitions of the π → п* and п* → π* types; these are quite insensitive to s-cis/s-trans isomerism.

Photoelectron and ultraviolet absorption spectra of allenyl vinyl ethers

The electronic structure of allenyl vinyl ethers (I) has been studied with the aid of photoelectron and UV spectroscopy, as well as MNDO and CNDO/S quantumchemical calculations. Divinyl ether has been selected as a model system for these molecules. The photoelectron spectra of I are similar to the spectrum of divinyl ether, with the exception of the band at 10.2–10.6 eV. The long-wavelength band in the UV spectra of I has been assigned to a transition localized in the allene group. The short-wavelength band of I corresponds to the π → π* transition observed in divinyl ether.

Rotational isomerism and calculation of the vibrational spectrum of methyl vinyl selenide

Summary1.Methyl vinyl selenide exists in the form of a mixture of rotational isomers.2.On the basis of a calculation of normal vibrations an assignment has been made of the absorption bands in the Raman and IR spectra of methyl vinyl selenide on the assumption that the planar cis-conformer is the most stable. The model of the force field used for the calculations gives satisfactory agreement with experiment.

Features of the electronic structure of molecules of vinyl sulfoxides and properties of their complexes with iodine and tetracyanoethylene

Conclusions1.The conjugation of the sulfoxide and vinyl groups is characterized by extensive restricting of their lowest unoccupied one-electron Π levels.2.The character of the conjugation of the sulfoxide group with the unsaturated and aromatic fragments accounts for the high sensitivity of the UV absorption spectra, the values of the first ionization potentials, and the positions of the charge-transfer bands for the CT complexes of organyl sulfoxides with electron acceptors to this effect and, accordingly, the low sensitivity of the values of the relative basicity and the dipole moments.3.Dialkyl sulfoxides, alkyl vinyl sulfoxides, and divinyl sulfoxide form CT complexes with iodine and tetracyanoethylene, whose heats of complexation and positions of λmax are determined primarily by the induction and resonance effects of the substituents attached to the sulfoxide group.

Vibrational spectrum of methyl vinyl telluride

Conclusion1.The bands in the Raman and IR spectra of methyl vinyl telluride were assigned on the basis of a normal mode calculation. The force field of the vinyl and methyl groups are generally satisfactorily transferable for methyl vinyl sulfide, methyl vinyl selenide, and methyl vinyl telluride.2.Analysis of the vibrational spectrum indicated that methyl vinyl telluride exists as two conformers. The β(TeCC) and γ(CTeC) vibrations are sensitive to change in the torsion angle.

Calculation of the vibrational spectra of methyl vinyl sulfide and its deuterated derivatives

Conclusions1.Vibrational spectra were obtained for methyl vinyl sulfide and its deuterated analogs and the band were assigned on the basis of normal mode analysis.2.The major differences in the vibrational spectra of methyl vinyl sulfide and methyl vinyl ether result from differences in the geometrical parameters of the CSC and COC fragments, difference in the mass of the S and O atoms, and difference in the electronegativities of these atoms.3.The vibrations whose frequencies are sensitive to rotational isomerism of methyl vinyl sulfide were established. The analysis shows that the C3SC1C2 torsional angle is about 135° in the less stable gauche conformer.

Ultraviolet absorption spectra of vinyl sulfides and selenides

Conclusions1.The short-wave and long-wave absorption bands of the vinyl sulfides and selenides have been assigned to the π→π* and n →σ*-transitions (or σ→σ*) respectively. In the spectra of divinyl sulfide and divinyl selenide two absorption bands are observed, corresponding to π → π*-transitions in the A1 and B2 states, as well as a band at due to the n → σ*-transition.2.The presence of two absorption bands in the UV spectra of the vinyl sulfides in the region 220–260 nm is not due to conformational isomerism.3.In comparison with the vinyl esters conjugation in the vinyl sulfides and selenides is characterized by intrinsically lower energies (0 > S < Se), but higher polarizability values of the molecules (0 < S < Se).

Spectroscopic study of the structure of o-substituted 2,4-dinitrophenylthiobenzoates and their alkaline hydrolysis kinetics

Conclusions1.The stereo structure of the o-substituted 2,4-dinitrophenylthiobenzoates depends on the nature of the substituent. Fluorine, chlorine, and methoxy derivatives exist in several nonequivalent conformations.2.Conjugation between the carbonyl group and the aromatic ring is conserved for all the compounds studied.3.The alkaline hydrolysis reaction rate rises as the constant σ* of the substituent increases.4.The alkaline hydrolysis reaction rate becomes less dependent on the nature of the substituent as the reaction temperature falls.