Yuri I. Binev

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.

Ab initio HF, density functional and experimental studies on the IR spectra and structure of 1,2-benzisothiazol-3-(2H)-thione-1,1-dioxide (thiosacchanin) and its nitranion.

The spectral and structural changes taking place in the course of the conversion of 1,2-benzisothiazol-3-(2H)-thione-1,1-dioxide (thiosaccharin) into a nitranion have been studied on the basis of both IR spectra and ab initio HF 6-31G(d) and BLYP 6-31G(d,p) force field calculations. The conversion causes nu(as)SO2 and nu(s)SO2 frequency decreases of 47 and 13 cm(-1), respectively, and other spectral changes. The nuC=S coordinate is strongly delocalized. The ab initio geometries of the isolated molecule and nitranion agree well with the single-crystal X-ray ones, determined for thiosaccharin and its sodium (potassium) monohydrate salts, respectively. The nitranionic charge is delocalized almost uniformly within the thiocarbonyl (0.29 e-), sulfonyl (0.24 e-), and phenylene (0.24 e-) groups, and the nitranionic center (0.23 e-).

Ab initio MO and experimental studies on the vibrational spectra and structure of 4-hydroxybenzonitrile and of its anion

Abstract The structures of 4-hydroxybenzonitrile (p-cyanophenol) and its anion have been studied by IR spectra and ab initio HF and MP2 calculations. In agreement between theory and experiment, the conversion of the 4-hydroxybenzonitrile molecule into the oxyanion leads to essential spectral changes: decrease in the frequency of the cyano stretching band and strong increase in its integrated intensity, strong enhancement of the integrated intensities of the aromatic skeletal bands of ν8 and ν19 types, etc. According to the calculations (MP2 data in italics) the oxyanionic charge is delocalized over the cyano group (0.13e−, 0.12e−), phenylene ring (0.44e−, 0.39e−) and oxyanionic center (0.43e−, 0.49e−). The conversion into the oxyanion results in an additional quinoidization of the phenylene ring.

The conversion of phenylpropanedinitrile (phenylmalononitrile) into the carbanion, followed by IR spectra, ab initio and DFT force field calculations

The spectral and structural changes, caused by the conversion of phenylpropanedinitrile (phenylmalononitrile) into the carbanion, have been followed by IR spectra, ab initio HF, MP2 and DFT BLYP force field calculations. In agreement between theory and experiment, the conversion is accompanied with strong frequency decreases (with 114 cm(-1), mean value) of the cyano stretching bands nu(C triple bond N), dramatic increases in the corresponding integrated intensities (136-fold, total value), strong enhancement of the nu(C triple bond N) vibrational coupling and other essential spectral changes. According to the calculations, the strongest structural changes take place at the carbanionic center: (i) shortenings of the Cz-Ph and Cz-CN bonds with 0.064-0.092 A, and increases in the corresponding bond orders with 0.14-0.21 U; (ii) simultaneous enlargements of the bond angles at the same carbon atom with 7.6 degrees -9.7 degrees, as from tetrahedral its configuration becomes trigonal. The carbanionic charge is distributed between the two cyano groups (0.44-0.52 e(-)), phenyl ring (0.31-0.34 e(-)) and carbanionic center (0.14-0.25 e(-)). The formation of moderately strong (CH(3))(2)S=O...H-C(CN)(2)C(6)H(5) hydrogen bonds has been found experimentally.

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.

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.

Experimental and ab initio MO studies on the IR spectra and structure of cyanoacetic acid, its oxyanion and dianion

Abstract The structures of cyanoacetic acid NCCH 2 CO 2 H, its oxyanion NCCH 2 CO 2 and dianion NCCHCO 2 − were studied by means of both IR spectra and ab initio HF and MP2 calculations. Both spectral and structural changes, accompanying the conversion of cyanoacetic acid into the oxyanion, are localized mainly within the carboxylato group; the oxyanion → dianion changes spread over the whole anionic species. The theory predicts qualitatively well the drastic frequency decrease (146 cm −1 ) and the intensity increase (34 fold) of the C  N stretching band, the carboxy → carboxylato IR changes etc. resulting from the conversions studied. The greater part (0.70 e − ) of the first (oxyanionic) electric charge remains localized within the carboxylato group; the second (carbanionic) charge is delocalized over the methide (0.43 e − ), carboxylato (0.29 e − ) and cyano (0.28 e − ) groups. The possible conformers of the cyanoacetic acid molecule are also discussed. The presence of solvent-separated ion pairs in the DMSO solutions of the alkali-metal mono- and di- derivatives of cyanoacetic acid is assumed.

Infrared spectra and structure of the cyano and methoxycarbonyl derivatives of 3,3-bis(dimethylamino)acrylonitrile: an ab initio force field treatment

Abstract The structure of 2-cyano-3,3-bis(dimethylamino)acrylonitrile and 2-methoxycarbonyl-3,3-bis(dimethylamino)acrylonitrile has been studied on the basis of both infrared spectra and ab initio force field calculations. The 3012–376 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 CC bond in the molecules studied is strongly polarized. The ground-state charge transfer between the electropositive and electronegative fragments of the molecules is more than 0.5 e − , so the species studied have a dual character, both molecular and zwitterionic.