Anwar S. El-Shahawy

Spectroscopic structural studies of salicylic acid, salicylamide and aspirin

Abstract The electronic absorption spectra of the salicylic acid and the salicylamide molecules have been studied using SCF—CL calculations. The singlet and the triplet electronic transition energies have been calculated. The state functions of eight excited states for these molecules have been calculated in addition to the oscillator strengths, charge densities, ionization potentials and electron affinities. Our calculations lead to the presence of salicylic acid and salicylamide in the β-forms in which the carboxylic hydroxyl group or the amino group is directed toward the enolic hydroxyl group. The salicylic acid and the salicylamide molecules have the C s point group symmetry, but the aspirin molecule has the C 1 point group symmetry, in which the acetyl group does not lie in the plane of the salicylic acid molecule.

Vibrational spectra of deuterated phenyl azide and 2,6-dimethylphenyl azide

Abstract The Raman and the i.r. spectra of deuterated phenyl azide have been measured. From the depolarization ratios and the assignments of the Raman bands, it has been concluded that the structure of this molecule has C s point group. The work has been extended to 2,6-dimethylphenyl azide, assuming it has C s or C 1 point group due to the presence of two methyl groups in the ortho positions.

Spectrophotometric study of acid-base equilibria of 4-(2-benzothiazolylazo)resorcinol and 4-(2-benzothiazolylazo)salicylic acid in water-organic solvent media

The visible absorption spectra of 4-(2-benzothiazolylazo)resorcinol (BTAR) and 4-(2-benzothiazolylazo)salicylic acid (BTAS) have been recorded in water-organic solvent mixtures in the pH range 0.5–12.0. The organic solvents used are methanol, ethanol,n-propanol, iso-propanol, acetone, dioxane and dimethyl formamide. The spectral changes have been explained in terms of shifts in equilibria among different molecular and ionic species of BTAR and BTAS existing in solution. The pKa values corresponding to the different ionization steps have been determined at 25°C and I=0.1M (KNO3) by graphic analysis of the absorbance-pH curves. The results obtained are discussed in terms of the molecular structure of the reagents and the nature of the organic co-solvent used.

Arylidene polymers: 11. Synthesis of poly[2,5-bis(m-nitrobenzylidene)-cyclopentanone sulphide] and some theoretical studies on its monomer unit

Abstract Nitration of 2,5-bis( p -chlorobenzylidene)cyclopentanone (I) afforded the corresponding 2,5-bis( p -chloro- m -nitrobenzylidene)cyclopentanone (II). Polymerization of II with Na 2 S in N -methylpyrrolidone gave poly[2,5-bis(3-nitrobenzylidene)cyclopentanone sulphide]. The monomer was characterized by infra-red and 1 H nuclear magnetic resonance spectroscopy and elemental analysis. The polymer formed was confirmed by elemental analysis, infra-red spectroscopy, viscometry, differential thermal analysis measurements, thermogravimetry and X-ray analysis. An isothermal electrical conductivity test of the new polysulphide polymer indicates that it has a value of about 3.2 × 10 −3 ohm −1 cm −1 at 390 K. Using the Pariser-Parr-Pople method the CO oxygen atom in compound II has a partially positive charge in the normal state, reduced and oxidized forms. The ionization potential and the electron affinity are not altered by replacing the sulphur atom, i.e. 9.55 (9.56) and 7.94 (7.77).

Nicotinic acid and nicotinamide electronic structural studies

Abstract After spectroscopic studies and SCF-CI calculations, it was concluded that nicotinic acid and nicotinamide have α-and β-forms. The β-conformer for nicotinic acid or nicotinamide has a higher π-electronic energy than the α-conformer by about 0.5 kcal mole−1. The electronic transition energies of the conformers show good agreement with the experimental data.

Electronic conformational studies of azidobenzene and azidobenzene derivatives

The Cs point group structure for azidobenzene in which the plane of symmetry passes through the plane of the benzene ring was verified by SCF-CI calculations. The calculations, which were extended to ortho- and meta-azidobenzoic acids and to p-azidoanisole, show that ortho- and meta-azidobenzoic acids exist only in the cis form with the hydroxyl group orientated towards the azide group (β form). The calculated transition energies are in good agreement with experimental data and the presence of one conformer for each molecule is confirmed.

Some CNDO Calculations and Structural Spectroscopic Studies of Paracetamol Complexes

Abstract Through complete neglect of differential overlap (CNDO) calculations of the electronic energy among different possible structures of paracetamol (PA) molecule, it has been concluded that its structure has Cs point group symmetry of the cis‐form in which the methyl group has a restricted free rotation around its bond with the carbon atom of the amide group. The electronic spectra of PA compound were studied in different polar and nonpolar solvents. The temperature effect on the electronic spectra confirms the presence of one conformer only. The hydrogen bonding and the orientation energies of the polar solvents were determined from the studies of mixed solvents. Complexes of PA with metal ions M(II) (Cu++, Zn++, or Fe++) of ratio 2:1, respectively, were prepared, and their structure has been confirmed by elemental analysis, atomic absorption spectra, IR spectra, and 1H‐NMR spectra. It has been concluded that the structure of the complexes has C2h point group symmetry in which two PA molecules are chelated to any one of the metal ions Cu++, Zn++, and Fe++.

Effect of the varying π-accepting properties of someortho-substituted benzoic acids on the stability of mixed-ligand complexes also containing quinizarin and thorium(IV)

The mixed-ligand complexes of thorium(IV) with quinizarin (quin) and as a second ligand,L, salicyclic acid (sa), thiosalicylic acid (tsa) or anthranilic acid (ant) were studied potentiometrically in 40% (v/v) ethanol-water medium [I=100 mmol dm−3 (KNO3), 25±0.1 °C]. The equilibria existing in solutions were demonstrated and the ternary stability constants of the 1:1:1 Th-quin-L-complexes were characterized. All of these biligand complexes are considerably more stable than the corresponding monoligand ones. In addition, the relatively most stable ternary complex is formed withant which is the best π-acceptor. The order of stability of the ternary complexes is in accordance with the calculated π-charge densities of the varying ligating group in the ligandL. The values of the equilibrium constants (log units) for the reaction: Th(quin)2+ThL2⇌2Th(quin)(L) are 2.47 (0.13), 2.60 (0.3) and 4.25 (0.86) for Th(quin)(tsa), Th(quin)(sa) and Th(quin)(ant), respectively. The constants given in parentheses correspond to Δ logKTh (= logKTh(quin)(L)Th(quin) — logKThLTh).ZusammenfassungDie gemischtligandigen Komplexe von Thorium(IV) mit Chinizarin (quin) und als zweiten Liganden (L) Salizylsäure (sa), Thisalizylsäure (tsa) oder Anthranilsäure (ant) wurden potentiometrisch in 40% (v/v) Ethanol-Wasser [I=100 mmol dm−3 (KNO3),t=25±0.1 °C] untersucht. Die vorliegenden Gleichgewichte wurden formuliert und die ternären Stabilitätskonstanten der 1:1:1 Th-quin-L-Komplexe bestimmt. Alle zweiligandigen Komplexe sind wesentlich stabiler als die entsprechenden Monoligand-Komplexe. Der relativ stabilste Komplex wurde mitant gebildet, daant der beste π-Acceptor ist. Die Reihung der relativen Stabilitäten stimmt mit den berechneten π-Elektronendichten der verschiedenen LigandenL überein. Die Werte der Gleichgewichtskonstanten (in log Einheiten) für die Reaktion Th(quin)2+ThL2⇌2Th(quin)(L) sind 2.47 (0.13), 2.60 (0.30) and 4.25 (0.86) für Th(quin)(tsa), Th(quin)(sa) bzw. Th(quin)(ant), wobei die Werte in Klammern ΔlogKTh = logKTh(quin)(L)/Th(quin) — logKThLTh entsprechen.

Spectrophotometric study of the complexation equilibria of lanthanum(III) with 1,4-bis(4′-methylanilino)anthraquinone and the determination of lanthanum(III)

The complexation equilibria of lanthanum(III) with 1,4-bis(4′-methylanilino)anthraquinone (Quinizarin Green) were studied spectrophotometrically in 40%V/V dimethylformamide using graphical analysis of the absorbance curves. The reaction mechanism of lanthanum with the bisarylaminoanthraquinone dye within the pH range 6–9.25 was demonstrated. The thermodynamic stabilities and the molar absorptivities of the complexes formed were determined. The optimum conditions for the spectrophotometric determination of La(III) with this reagent were found.

Molecular complex formation of thiosalicylic acid with ethanol

Abstract The formation of a 1:1 molecular complex of thiosalicylic acid (TSA) with ethanol was studied spectrophotometrically. Ethanol is postulated to form an intermolecular hydrogen bond with the carboxyl OH group of TSA, the intramolecular hydrogen bond of the SH group remaining intact. Results of SCF-CI molecular orbital calculations support the spectral interpretation. The formation constant ( K ⨍ ), free energy change (Δ G ) and molar absorptivity of the TSA-ethanol molecular complex with cyclohexane, CCl 4 or CHCl 3 as solvents were determined. K ⨍ values vary with solvent in the order cyclohexane > CCl 4 > CHCl 3 . The electronic absorption spectra of TSA in one- and two-component solvents are discussed.