Evelina A. Velcheva

The infrared spectra and structure of o-sulfobenzimide (saccharin) and of its nitranion: An ab initio force field treatment

The structure of o-sulfobenzimide (saccharin) and of its nitranion has been studied on the basis of both infrared spectra and ab initio force field calculations. A good agreement has been found between the theoretical and experimental spectroscopic characteristics of the particles studied. The theoretical method used gives a good description of the strong spectral changes caused by the conversion of the saccharin molecule into the corresponding nitranion. The structural changes which accompany this conversion are essential and they spread over the whole sulfocarboximide group and the adjacent bonds. The nitranionic charge is delocalized over the phenylene group (0.29 e−), sulfonyl group (0.26 e−), nitranionic center (0.25 e−), and carbonyl group (0.20 e−).

Infrared spectra and structure of phenylacetonitrile and of its carbanion: an ab initio force field treatment

Abstract The structures of phenylacetonitrile and of its carbanion have been studied on the basis of IR spectroscopic data (including literature results) and of ab initio force field calculations. The assignment (D. Croisat et al., J. Org. Chem., 157 (1992) 6435) of the IR bands of phenylacetonitrile, its d 5 analogue, and their carbanions has been confirmed. An excellent linear correlation ( R = 0.999) has been found between the theoretical and experimental IR frequencies of the species studied. The calculations predict well the strong increase in intensity (five to 42 fold) of the v CN , v S8 and v I9 bands which accompanies the conversion of the phenylacetonitrile molecule to its carbanion. The structures of both sodium and potassium derivatives of phenylacetonitrile in dimethyl sulfoxide are close to that of the kinetically free phenylacetonitrile carbanion. The carbanionic center is practically planar; the cyano group carries a considerable negative charge, but its influence on the carbanionic center is mainly inductive. The carbanionic charge is delocalized over the phenyl ring (0.42 e − ), methide (0.30 e − ), and cyano (0.28 e − ) groups.

IR spectral and structural changes caused by the conversion of 3-hydroxybenzaldehyde into the oxyanion

The spectral and structural changes, caused by the conversion of the 3-hydroxybenzaldehyde molecule into the corresponding oxyanion have been studied by IR spectra, and MP2 and DFT force field calculations. The conversion causes a 13 cm(-1) decrease in the frequency of the carbonyl stretching band nu(Cz=O), a 1.3-fold increase in its integrated intensity, strong intensity increases (2.1-5.3-fold) of the aromatic skeletal nu8 and nu19 as well as formyl nu(CH) bands. According to the calculations the oxyanionic charge is delocalized over aldehyde group (0.37 e-), phenylene ring (0.12 e-) and oxyanionic center (0.52 e-). The conversion into the oxyanion leads to geometry changes in the whole species, but it remains planar.

IR studies in the substituted benzaldehyde series provide a new definition of sigma-plus constants of ionic substituents

Fourier-transform IR frequencies nu(C=O) and integrated intensities A(C=O) of the carbonyl groups of a series of benzaldehydes (53 compounds) have been measured in dimethyl sulphoxide. Excellent and satisfactory correlations have been found between nu(C=O) and sigma(+) substituent constants of the m- and p-substituted compounds. Diortho-substituted compounds deviate strongly from the correlation lines because of the steric ortho-effects mainly. sigma(+) constants of ionic substituents (10 examples) have proved satisfactorily valid in the series studied.

On the validity of the constants of ionic substituents. Substituent effects on the cyano stretching frequencies and intensities of trans-α-phenyl-β-arylacrylonitriles

Fourier-transform IR frequencies ν(CN) and integrated intensities A(CN) of the cyano groups of a series of trans-α-phenyl-β-arylacrylonitriles (51 compounds) have been measured. Both ν(CN) and the square roots of A(CN) of the neutral m- and p-substituted compounds (34 examples) have been found to correlate satisfactorily with σ1 substituent constants, as well as according to the equation of Yukawa-Tsuno. Diortho-substituted compounds deviate strongly from the correlation lines because of the steric ortho-effects mainly. σ+ (and other) constants of ionic substituents (seven examples) have proved satisfactorily valid in the series studied. The transmission coefficient of the CC double bond in the series has been estimated to be 0.7.

IR STUDIES ON THE VALIDITY OF CONSTANTS OF IONIC SUBSTITUENTS IN THE BENZYLIDENEMALONONITRILE SERIES

Abstract Fourier-transform IR frequencies and integrated intensities of the cyano groups of a series of benzylidenemalononitriles (34 compounds) have been measured in dimethyl sulphoxide. Excellent and satisfactory correlations have been found between spectroscopic features and substituent constants. σ+ (and other) constants of ionic substituents (three examples) have proved satisfactorily valid in the series studied. The C=C bridge transmits the substituent effects on the intensities twice as strong than the effects of the same substituents on the corresponding frequencies.

Vibrational spectra of 2-phenyl-indane-1,3-dione, its isotopic labelled derivatives and the corresponding carbanions

Abstract IR and Raman spectra of 2-phenyl-indane-1,3-dione d 0 , d 4 , d 5 , d 10 , and 18 O have been measured in both the solid state and solution in the 4000–100 cm −1 frequency region. IR and Raman spectra of the corresponding carbanions have also been measured in DMSO-d 6 solutions in the 2000–1100 cm −1 frequency range. The assignment of the spectra of the neutral compounds is performed using the group vibrational concept and the isotopic shifts of the normal modes. The assignment of the bands in the IR and Raman spectra of the corresponding carbanions is made on the basis of isotopic shifts and the spectral changes accompanying the conversion of the neutral compounds into carbanions. The conversion of the parent β -diketone into carbanion causes a ca. 160 cm −1 decrease in the frequency of the anti-phase ν CO bands; this results is explained by the high mobility of the carbanionic charge.

Characterization of Zahari Zograph's nave wall paintings in the church "The nativity of the virgin" of Rila Monastery (Bulgaria) by vibrational spectroscopy and SEM-EDX analysis

ABSTRACT An analytical study on the nave mural paintings of the church “The Nativity of the Virgin” of Rila monastery, Bulgaria, painted by Zahari Zograph was carried out. Vibrational spectroscopy was applied to identify the pigments and organic materials used in the mural paintings. To complement the spectral information, elemental composition of the samples was determined by SEM-EDX. The data showed that smalt with carbohydrate binder was applied for the blue background, green colour was executed by green earths and red-orange colour – by red lead. Azurite is the pigment used to paint the blue colour of the saints’ hoods. The mordant for gilding was prepared of drying oil, resin and siccative metal oxides as evidenced by SEM-EDX, ATR-FTIR and pyrolysis GC-MS analysis. The use of azurite is related to Zahari Zograph’s works as it was not found in any of the previously studied murals in the church painted by other artists.

Vibrational spectra of 3-benzylidenephthalide and its 18O-labelled derivative

Abstract Infrared and Raman spectra of 3-benzylidenephthalide and 3-benzylidenephthalide-18O have been measured in solid state and in solution in the 4000–50 cm−1 frequency region. Their linear dichroic infrared spectra in oriented nematic solutions in the liquid crystal ZLI-1538 (4000–400 cm−1) have also been recorded and studied. The complete empirical assignment of the vibrational bands is performed using the group vibrational concept, isotopic shifts and polarization features of the normal modes.