Ivan G. Binev

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−).

Experimental and ab initio MO studies on the IR spectra and structure of 4-hydroxyacetanilide (paracetamol), its oxyanion and dianion

Abstract The spectral and structural changes taking place during the course of the conversion of 4-hydroxyacetanilide (paracetamol), HOC 6 H 4 NHCOCH 3 , into the corresponding oxyanion, − OC 6 H 4 NHCOCH 3 , and dianion, − OC 6 H 4 NCOCH 3 , have been followed by both quantitative infrared spectra and ab initio HF/6–31G force-field calculations. The changes accompanying the first deprotonation concern mainly the oxyphenylene fragment; those resulting from the second one are spread over the whole dianion. Analysis of the atomic charge changes shows that over 90% of the first (oxyanionic) charge remains localized within the oxyphenylene fragment. The second (nitranionic) charge delocalizes over the acetyl (0.51 e − ) and phenylene (0.26 e − ) groups, nitranionic (0.14 e − ) and oxyanionic (0.09 e − ) centres. The trans conformers (with respect to phenylene and methyl groups) have been calculated to be more stable than the cis ones in all cases studied.

IR spectra and structure of benzylidenemalononitrile and its cyanide, methoxide and heptylamine adducts: experimental and ab initio studies

Abstract The potassium cyanide, alkali-metal methoxide and heptylamine adducts of benzylidenemalononitrile were prepared as dimethyl sulphoxide (DMSO) and DMSO- d 6 solutions; their structures were studied by IR spectroscopy and ab initio force field calculations. The cyanide and methoxide adducts have a carbanionic structure, whereas heptylamine forms a zwitterion. The IR spectra of the adducts studied are characterized by very intense, low-frequency ν CN bands with a strong ν CN s – ν CN as splitting. The changes in the structure and force field of benzylidenemalononitrile accompanying its conversion into the adducts studied are essential and are spread over the whole molecule. The anionic charge is localized mainly within the dicyanomethide groups of the adducts.

The infrared spectra and structure of acetylsalicylic acid (aspirin) and its oxyanion: an ab initio force field treatment

Abstract The structures of acetylsalicylic acid (aspirin) (I) and its oxyanion (II) have been studied by means of infrared spectra and ab initio 3–21 G force field calculations. The 3100-1100 cm −1 region bands of both the aspirin molecule and its oxyanion have been assigned. The theoretical infrared data for the free aspirin anion are in good agreement with the experimental data for aspirin alkali-metal salts in dimethyl sulfoxide- d 6 . The theoretical geometrical parameters for the isolated aspirin molecule are close to the literature X-ray diffraction data for its dimer in the solid state, except for those of the carboxy group, which participates directly in hydrogen bond formation. The changes in both the spectral and geometrical parameters, caused by the conversion of the aspirin molecule into the anion, are essential, but they are localized mainly within the carboxy group and the adjacent C-Ph bond. This is also true for the changes in the corresponding bond indices and electronic charges.

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.

Infrared spectra and structure of alkane- and cycloalkanecarbonitriles and of their carbanions: An ab initio force field treatment

Abstract The structure of alkane- and cycloalkanecarbonitriles (seven compounds) and of their carbanions has been studied by both infrared spectrometry and ab initio force field calculations. The carbanions (counter ions Li + , Na + and K + ) have been found to exist mainly as ionic aggregates in hexamethylphosphoric triamide solutions. The calculations describe well the marked decrease, by 124–214 cm −1 , in the nitrile band frequencies and also the strong increase, by 1–2 orders, in the nitrile band integrated intensities which accompany the conversion of the parent neutral molecules into carbanions. Cyclopropanecarbonitrile is remarkable as having the highest nitrile band intensity among all the neutral molecules and the lowest one among all the carbanions studied. This result has also been predicted by the calculations, and it can be explained by certain peculiarities in the structure of the particles. The conjugation of the carbanionic charge with the cyano group in the cyclopropanecarbonitrile carbanion is greatly hindered by the considerable deviation (estimated at 56°) of the cyano group from the ring plane. The carbanionic charges of the carbanions studied are delocalized over the cyano groups (0.30–0.41 e − ), carbanionic centres (0.08–0.29 e − ) and hydrocarbon moieties (0.34–0.63 e − ).

Experimental and ab initio MO studies on the IR spectra and structure of cyanoacetamide, its carbanion and dianion

Abstract The structures of cyanoacetamide NC–CH2–CONH2, its carbanion NC− C H−CONH 2 and dianion NC− C H−CO N H , and of their perdeutero and 15N labelled analogues have been studied by means of both IR spectra and ab initio HF 6-31G and 6-31+G(d) calculations. Both the spectral and structural changes, accompanying the conversion of cyanoacetamide into the carbanion, spread over the whole molecule; the carbanion → dianion changes are localized mainly within the carboxamido group. The theory predicts qualitatively well the strong frequency decreases (165 and 247 cm−1) and the strong intensity increases (29 fold and 1.7 fold) of the CN and CO stretching bands respectively, resulting from the conversions studied. The first (carbanionic) electric charge is delocalized over the methide (0.36 e−), carboxamide (0.33 e−) and cyano (0.31 e−) groups; the greater part (0.74 e−) of the second (nitranionic) charge remains localized within the carboxamido group. The possible conformers of the species studied are also discussed. The anionic species exist as ion pairs in dimethyl sulfoxide solutions.

Infrared spectra and structure of butyldimethylammonium dicyanomethylide: an ab initio force field treatment

Abstract The structure of butyldimethylammonium dicyanomethylide has been studied on the basis of both infrared spectra and ab initio force field calculations. The 3031-416 cm −1 region bands have been assigned; a good agreement has been found between the theoretical and experimental spectroscopic characteristics. According to both infrared data and bond parameters, the dicyanomethide group in the molecule studied has a pronounced anionic character. However the analysis of the net atomic charges indicates at an only moderate (0.45 e − ) charge transfer between the ammonium and the dicyanomethide fragments of the butyldimethylammonium dicyanomethylide molecule.

Experimental and ab initio MO studies on the IR spectra and structure of pyridinium dicyanomethylide and trimethylammonium dicyanomethylide.

The structures of the title ylides have been studied by both quantitative infrared (IR) spectra and ab initio HF and MP2 force field calculations. Good agreement has been found between theoretical and experimental data for their spectral and structural characteristics. According to both IR data and geometry parameters the dicyanomethide groups in the ylides studied have a pronounced carbanionic character. The analysis of the calculated net electric charges however shows only moderate (below 0.6 e-) intramolecular charge transfers between the pyridinium (trimethylammonium) and dicyanomethide fragments of the species studied.

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.