Dr Ahmed El Defrawy | Mansoura University (original) (raw)

Papers by Dr Ahmed El Defrawy

Research paper thumbnail of Synthesis and Characterization of New Transition Metal Complexes of Schiff-base Derived from 2-Aminopyrimidine and 2,4-Dihydroxybenzaldehyde and Its Applications in Corrosion Inhibition

ABSTRACT. New complexes cis-[Mo2O5(Hapdhba)2], trans-[UO2(Hapdhba)2], [Pd(Hapdhba)Cl(H2O)], [Pd(b... more ABSTRACT. New complexes cis-[Mo2O5(Hapdhba)2], trans-[UO2(Hapdhba)2], [Pd(Hapdhba)Cl(H2O)], [Pd(bpy)(Hapdhba)]Cl, [Ag(bpy)(Hapdhba)], [Ru(Hapdhba)2(H2O)2], [Rh(Hapdhba)2Cl(H2O)] and [Au(Hapdhba)Cl2] are reported, where H2apdhba is the Schiff-base derived from 2-aminopyrimidine and 2,4-dihydroxy benzaldehyde. The complexes were characterized by IR, electronic, 1H NMR and mass spectra, conductivity, magnetic and thermal measurements. The inhibitive effect of H2apdhba for the corro-sion of copper in 0.5 M HCl was also determined by potentiodynamic polarization measurements.

Research paper thumbnail of Theoretical Study of the Tautomeric Preference and Self Association Processes of 2-Pyrrolidinone

Relative tautomerization energies, dipole moments for the tautomers of 2-pyrrolidinone was studie... more Relative tautomerization energies, dipole moments for the tautomers of 2-pyrrolidinone was studied by quantum-chemical calculations, using the B3LYP level of calculation with the 6-311G(d,p) basis set in the gas phase with full geometry optimization. Entropies, enthalpies and Gibbs free energies for the tautomerization process of 2-pyrrolidinone was obtained using the RHF/6-31G(d) level of computation. The calculations showed that, the Keto form is the most stable form in the gas phase. The entropy effect on the Gibbs free energy change of the tautomerization process 2-pyrrolidinone is found to be very small, and has practically no significance for the tautomeric equilibria of the 2-pyrrolidinone. The enthalpic term is dominant in the determination of the equilibrium constant. The ability to form dimer, trimer and tetramer was investigated concerning the energetical changes; dipole moments using the RHF/6-31Gd level of computation. The thermodynamic parameters at different temperatu...

Research paper thumbnail of Spectroscopic, Voltammetric, DFT and Molecular Docking Studies of Copper (II) Complex of Carbothiohydrazide Derivative

In this work, the nature of complexation between copper and N′,2-bis((E)-2hydroxybenzylidene) hyd... more In this work, the nature of complexation between copper and N′,2-bis((E)-2hydroxybenzylidene) hydrazine-1-carbothiohydrazide (a promising metal sensing Schiff base with a marked biological activity) (H4L) has been investigated and experimentally characterized. The investigation includes spectroscopic tools as infrared spectra (FT-IR), XRD, thermal analysis (TG) Raman spectra, UV-Vis, in addition to cyclic voltammetric study. Quantum chemical calculations using density functional theory (DFT) used to predict the structural properties of the complex under investigation and to aid in the explanation of the electronic spectra of the complex. In addition to that, the Molecular docking for the complex under investigation with the 2ylh target protein have been conducted in order to check the biological activity of the complex.

Research paper thumbnail of Infrared and Raman spectra, conformational stability, structural parameters, ab initio calculations and vibrational assignments of aminodifluorophosphine

Journal of Molecular Structure, 2008

Infrared spectra (4000–50 cm−1) have been recorded for three isotopomers of aminodifluorophosphin... more Infrared spectra (4000–50 cm−1) have been recorded for three isotopomers of aminodifluorophosphine, H2NPF2, H215NPF2 and D2NPF2, of the gases. The Raman spectra of all three molecules were recorded of the liquids. To support the vibrational assignment MP2(full) ab initio calculations with the 6-31G(d) basis set were carried out to predict the fundamental vibrational frequencies, infrared intensities, Raman activities, depolarization values and infrared band contours. Additional ab initio calculations employing a variety of basis sets with and without diffuse functions have been used to predict the conformational stability, structural parameters and centrifugal distortion constants. These predictions are compared to previously reported experimental values when available. The adjusted r0 structural parameters have been obtained by systematically fitting the MP2(full)/6-311+G(d) predicted values with the previously reported rotational constants for five isotopomers obtained from the mi...

Research paper thumbnail of Synthesis and Quantum Chemical Studies on the Tautomeric Structures of New Thiazole and Thiadiazine Derivatives

Current Organic Synthesis, 2016

Research paper thumbnail of A Facile Access and Computational Studies of Some New 4,5'-Bipyrazole Derivatives

Research paper thumbnail of Conformational stability, ro structural parameters, ab initio calculations, and vibrational assignment for cyanocyclopentane

Vibrational Spectroscopy, 2010

Research paper thumbnail of Conformational Stability, ro Structural Parameters, Ab Initio Calculations, and Vibrational Assignment for Fluorocyclopentane

The Journal of Physical Chemistry a, 2009

Research paper thumbnail of Conformational Stability from Variable-Temperature Infrared Spectra of Krypton Solutions, Ab Initio Calculations, and ro Structural Parameters of Chlorocyclopentane

Structural …, 2003

(1.73 ± 0.18 kJ-mol −1 ) has been obtained with theaxialconformer the more stable form. It is est... more (1.73 ± 0.18 kJ-mol −1 ) has been obtained with theaxialconformer the more stable form. It is estimated that there is 67 ± 2% of the axial conformer present at ambient temperature. Convincing spectroscopic evidence shows that a significant percentage of the chlorocyclopentane ...

Research paper thumbnail of Theoretical and Experimental Study on the Effect of End Chain Length on Ultraviolet Absorption Behavior and Photostability of Alkoxy Benzoate Based Liquid Crystals

Oriental Journal of Chemistry

Research paper thumbnail of Synthesis of some novel antioxidant and anticorrosive additives for Egyptian gasoline motor oils

Ghada Elbana, 2011

2-Methyl-benzo[d][1,3]oxazin-4-one (1) was used as a key intermediate for the synthesis of differ... more 2-Methyl-benzo[d][1,3]oxazin-4-one (1) was used as a key intermediate for the synthesis of different benzoxazinone and quinazolinone derivatives. In order to evaluate the applicability of the synthesised benzoxazinones and quinazolinones as antioxidant additives for lube oil, these antioxidant additives decomposed the alkyl peroxide radicals and/or alkyl hydrogen peroxides to produce esters, ketone and hydroxy compounds rather than carboxylic acids. The compounds that showed antioxidant efficiency were tested as corrosion inhibitors using three types of metals: Cu, Al and Fe.

Research paper thumbnail of Conformational Stability, r0 Structural Parameters, Ab Initio Calculations, and Vibrational Assignment for Fluorocyclopentane

J Phys Chem a, 2009

The infrared spectra (3200-50 cm-1) of the gas and solid and the Raman spectrum (3200-30 cm-1) of... more The infrared spectra (3200-50 cm-1) of the gas and solid and the Raman spectrum (3200-30 cm-1) of liquid and solid fluorocyclopentane, c-C5H9F, have been recorded. Additionally the infrared spectra (3200-400 cm-1) of liquid xenon solutions have been recorded at -65 and -95 °C. In all of the physical states, only the twisted C1 conformer was detected. Ab initio calculations utilizing various basis sets up to MP2(full)/6-311+G(2df,2pd) with and without diffuse functions have been used to predict the conformational stabilities. These calculations predict only the twisted C1 conformer as the stable form. The two envelope (Cs symmetry) forms with axial and equatorial structures were predicted to be first order saddle points with average higher energies of 75 ± 33 and 683 ± 44 cm-1, respectively, from the C1 conformer but lower energies of 2442 and 1812 cm-1, respectively, than the planar form by MP2 calculations. Similar values were obtained from the corresponding density functional theory calculations by the B3LYP method. A complete vibrational assignment is given for the twisted (C1) conformer which is supported by normal coordinate calculations with scaled force constants from MP2(full)/6-31G(d) calculations. The adjusted r0 structural parameters have been obtained by systematically fitting the MP2(full)/6-311+G(d,p) predicted values with the rotational constants obtained from a microwave study. The determined heavy atom r0 distances in Å are (C1C2) = 1.531(3), (C1C3) = 1.519(3), (C2C4) = 1.553(3), (C3C5) = 1.533(3), (C4C5) = 1.540(3), and (C1F6) = 1.411(3) and the angles in degrees are ∠C3C1C2 = 105.5(5), ∠C1C2C4 = 106.2(5), ∠C1C3C5 = 102.9(5), ∠F6C1C2 = 108.9(5), and ∠F6C1C3 = 107.6(5) with a dihedral angle ∠C2C4C5C3 = 25.3(3). These experimental and theoretical results are compared to the corresponding quantities of some similar molecules.

Research paper thumbnail of Vibrational spectra, r 0 structural parameters, barriers to internal rotation, and ab initio calculations of ClCH 2SiH 3, Cl 2CHSiH 3, ClCH 2SiF 3 and Cl 2CHSiF 3

Research paper thumbnail of Lornoxicam & Tenoxicam Drugs as Green Corrosion Inhibitors for Carbon Steel in 1 M H 2 SO 4 Solution

Inhibition performance of Lornoxicam & Tenoxicam against corrosion of carbon steel in 1 M H2SO4 s... more Inhibition performance of Lornoxicam & Tenoxicam against corrosion of carbon steel in 1 M H2SO4 solutions was investigated by weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements. The inhibition efficiency increased with increasing inhibitor's concentration, but decreased with increase in temperature. Potentiodynamic polarization curves showed that, the inhibitors were of mixed type. The apparent activation energy (E-a*) and other thermodynamic parameters for the corrosion process have also been calculated and discussed. The inhibition of carbon steel corrosion is due to the adsorption of the inhibitor molecules on the surface, which follows Temkin adsorption isotherm. The mechanism of inhibition was discussed in the light of the chemical structure of the undertaken inhibitors.

Research paper thumbnail of Theoretical Study of the Tautomeric Preference and Self Association Processes of 2-Pyrrolidinone

Relative tautomerization energies, dipole moments for the tautomers of 2-pyrrolidinone was studie... more Relative tautomerization energies, dipole moments for the tautomers of 2-pyrrolidinone was studied by quantum-chemical calculations, using the B3LYP level of calculation with the 6-311G(d,p) basis set in the gas phase with full geometry optimization. Entropies, enthalpies and Gibbs free energies for the tautomerization process of 2-pyrrolidinone was obtained using the RHF/6-31G(d) level of computation. The calculations showed that, the Keto form is the most stable form in the gas phase. The entropy effect on the Gibbs free energy change of the tautomerization process 2-pyrrolidinone is found to be very small, and has practically no significance for the tautomeric equilibria of the 2-pyrrolidinone. The enthalpic term is dominant in the determination of the equilibrium constant. The ability to form dimer, trimer and tetramer was investigated concerning the energetical changes; dipole moments using the RHF/6-31Gd level of computation. The thermodynamic parameters at different temperatu...

Research paper thumbnail of Synthesis, Cytotoxicity Evaluation, DFT Molecular Modeling Studies and Quantitative Structure Activity Relationship of Novel 1,8-Naphthyridines

American Journal of Organic Chemistry, 2012

Research paper thumbnail of Conformational Stability from Variable Temperature FT-IR Spectra of Krypton Solutions, r 0 Structural Parameters, Vibrational Assignment, and a b Initio Calculations of 4-Fluoro-1-butene

The Journal of Physical Chemistry A, 2008

The infrared spectra of gaseous and variable-temperature liquid xenon solutions of pyrrolidine ha... more The infrared spectra of gaseous and variable-temperature liquid xenon solutions of pyrrolidine have been recorded. The enthalpy difference has been determined to be 109 ± 11 cm(-1) (1.30 ± 0.13 kJ mol(-1)) with the envelope-equatorial conformer more stable than the twist form with 37 ± 3% present at ambient temperature. Ab initio calculations utilizing various basis sets up to MP2(full)/aug-cc-pVTZ have been used to predict the conformational stabilities, energy at the equatorial-axial saddle point, and barriers to planarity. From previously reported microwave rotational constants along with MP2(full)/6-311+G(d,p) predicted structural values, adjusted r(0) parameters have been obtained for both conformers. Heavy atom distances (Å) of equatorial[twist] conformer are as follows: N(1)-C(2) = 1.469(3)[1.476(3)], N(1)-C(3) = 1.469(3)[1.479(3)], C(2)-C(4) = 1.541(3)[1.556(3)], C(3)-C(5) = 1.541(3)[1.544(3)], C(4)-C(5) = 1.556(3)[1.543(3)]; and angles (deg)∠N(1)C(2)C(4) = 102.5(5)[107.6(5)], ∠N(1)C(3)C(5) = 102.5(5)[105.4(5)], ∠C(2)C(4)C(5) = 104.3(5)[104.6(5)], ∠C(3)C(5)C(4) = 104.3(5)[103.7(5)], ∠C(2)N(1)C(3) = 104.1(5)[103.9(5)], τC(2)C(4)C(5)C(3) = 0.0(5)[13.5(5)]. A complete vibrational assignment is proposed for both conformers.

Research paper thumbnail of Conformational stability of chlorocyclohexane from temperature-dependent FT-IR spectra of xenon solutions, r 0 structural parameters, and vibrational assignment

Structural Chemistry, 2008

Research paper thumbnail of Vibrational spectrum, conformational stability, structural parameters and ab initio calculations of dimethylaminodifluorophosphine

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2008

From analysis of the infrared and Raman spectra along with support from the ab initio predictions... more From analysis of the infrared and Raman spectra along with support from the ab initio predictions it is concluded that there is only one stable conformer of dimethylaminodifluorophosphine, (CH(3))(2)NPF(2), in the gaseous and liquid phases which has a planar PNC(2) moiety with C(s) symmetry. The adjusted r(0) structural parameters have been obtained by combining the MP2(full)/6-311+G(d) predicted values with the previous reported rotational constants for four isotopomers obtained from previously reported microwave studies. The difference in the two NC distances is 0.002A whereas, these two parameters were previously assumed to have the same values from the microwave and electron diffraction studies but a reported difference of 0.025A from the structural parameters of the crystal. The adjusted r(0) heavy atom distances and angles are: r(PF)=1.593(3); r(NP)=1.654(3); r(NC(i))=1.455(3); r(NC(o))=1.453(3) A; angleFPF=93.5(5); angleNPF=100.8(5); angleCNC=116.0(5); angleC(i)NP=124.1(5); angleC(o)NP=120.0 degrees . The planar bonding around the nitrogen atom is consistent with the previously reported structural information from the microwave study but differs from the slightly pyramidal bonding obtained in the electron diffraction investigation. To support the vibrational assignment MP2(full) ab initio calculations with the 6-31G(d) basis set were carried out to predict the fundamental vibrational frequencies, infrared intensities, Raman activities, depolarization values, infrared band contours, and centrifugal distortion constants. Vibrational assignments are given for (CH(3))(2)NPF(2) and (CD(3))(2)NPF(2) and comparisons are made with the predicted intensities, frequencies and centrifugal distortion constants. Frequencies of some of the lattice modes are reported from both the infrared and Raman spectra with suggested assignments based on the factor group symmetry of the crystal of D(2h)(16) (Pnma) with four molecules per primitive cell. These results are compared to the corresponding quantities of some similar molecules.

Research paper thumbnail of Conformational stability of cyclobutanol from temperature dependent infrared spectra of xenon solutions, r0 structural parameters, ab initio calculations and vibrational assignment

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2008

Variable temperature (-55 to -100 degrees C) studies of the infrared spectra (4000-400 cm(-1)) of... more Variable temperature (-55 to -100 degrees C) studies of the infrared spectra (4000-400 cm(-1)) of cyclobutanol, c-C4H7OH dissolved in liquid xenon have been carried out. The infrared spectrum (4000-100 cm(-1)) of the gas has also been recorded. From these data two of the four possible stable conformers have been confidently identified and their order of stabilities has been experimentally determined where the first indicator is for the position of attachment of the hydroxyl group on the bent cyclobutyl ring (Eq=equatorial or Ax=axial) and the second one (t=trans, g=gauche) is the relative position of the hydroxyl rotor, i.e. rotation around the ring C-O bond. The enthalpy difference between the most stable Eq-t conformer and the second most stable rotamer, Eq-g, has been determined to be 200+/-50 cm(-1) (2.39+/-0.60 kJ/mol). This experimentally determined order is consistent with the order of stability predicted by ab initio calculations Eq-t>Eq-g>Ax-g>Ax-t. Evidence was obtained for the third conformer Ax-g which is predicted by ab initio calculations to be less stable by more than 650cm(-1) than the Eq-t form. The percentage of each conformer at ambient temperature is estimated to be Eq-t (50%), Eq-g (47%) and Ax-g (3%). The conformational stabilities, harmonic force fields, infrared intensities, Raman activities, depolarization ratios and vibrational frequencies have been obtained for all of the conformers from MP2(full)/6-31G(d) ab initio calculations. The optimized geometries and conformational stabilities have been obtained from ab initio calculations utilizing several different basis sets up to MP2(full)/aug-cc-pVTZ and from density functional theory calculations by the B3LYP method. By utilizing previously reported microwave rotational constants for the Eq-t conformer combined with ab initio MP2(full)/6-311+G(d,p) predicted structural values, adjusted r0 parameters have been obtained. The determined heavy atom structural parameters for the Eq-t conformer are: the distances C1-C4=1.547(5) angstroms, C4-C6=1.552(5)angstroms, C-O=1.416(5) angstroms and angles angleC6C4C1=86.6(5) degrees , angleC4C1C5=88.9(5) degrees and angleC6C5C1C4=22.8(5) degrees . The results are discussed and compared to the corresponding properties of some similar molecules.

Research paper thumbnail of Synthesis and Characterization of New Transition Metal Complexes of Schiff-base Derived from 2-Aminopyrimidine and 2,4-Dihydroxybenzaldehyde and Its Applications in Corrosion Inhibition

ABSTRACT. New complexes cis-[Mo2O5(Hapdhba)2], trans-[UO2(Hapdhba)2], [Pd(Hapdhba)Cl(H2O)], [Pd(b... more ABSTRACT. New complexes cis-[Mo2O5(Hapdhba)2], trans-[UO2(Hapdhba)2], [Pd(Hapdhba)Cl(H2O)], [Pd(bpy)(Hapdhba)]Cl, [Ag(bpy)(Hapdhba)], [Ru(Hapdhba)2(H2O)2], [Rh(Hapdhba)2Cl(H2O)] and [Au(Hapdhba)Cl2] are reported, where H2apdhba is the Schiff-base derived from 2-aminopyrimidine and 2,4-dihydroxy benzaldehyde. The complexes were characterized by IR, electronic, 1H NMR and mass spectra, conductivity, magnetic and thermal measurements. The inhibitive effect of H2apdhba for the corro-sion of copper in 0.5 M HCl was also determined by potentiodynamic polarization measurements.

Research paper thumbnail of Theoretical Study of the Tautomeric Preference and Self Association Processes of 2-Pyrrolidinone

Relative tautomerization energies, dipole moments for the tautomers of 2-pyrrolidinone was studie... more Relative tautomerization energies, dipole moments for the tautomers of 2-pyrrolidinone was studied by quantum-chemical calculations, using the B3LYP level of calculation with the 6-311G(d,p) basis set in the gas phase with full geometry optimization. Entropies, enthalpies and Gibbs free energies for the tautomerization process of 2-pyrrolidinone was obtained using the RHF/6-31G(d) level of computation. The calculations showed that, the Keto form is the most stable form in the gas phase. The entropy effect on the Gibbs free energy change of the tautomerization process 2-pyrrolidinone is found to be very small, and has practically no significance for the tautomeric equilibria of the 2-pyrrolidinone. The enthalpic term is dominant in the determination of the equilibrium constant. The ability to form dimer, trimer and tetramer was investigated concerning the energetical changes; dipole moments using the RHF/6-31Gd level of computation. The thermodynamic parameters at different temperatu...

Research paper thumbnail of Spectroscopic, Voltammetric, DFT and Molecular Docking Studies of Copper (II) Complex of Carbothiohydrazide Derivative

In this work, the nature of complexation between copper and N′,2-bis((E)-2hydroxybenzylidene) hyd... more In this work, the nature of complexation between copper and N′,2-bis((E)-2hydroxybenzylidene) hydrazine-1-carbothiohydrazide (a promising metal sensing Schiff base with a marked biological activity) (H4L) has been investigated and experimentally characterized. The investigation includes spectroscopic tools as infrared spectra (FT-IR), XRD, thermal analysis (TG) Raman spectra, UV-Vis, in addition to cyclic voltammetric study. Quantum chemical calculations using density functional theory (DFT) used to predict the structural properties of the complex under investigation and to aid in the explanation of the electronic spectra of the complex. In addition to that, the Molecular docking for the complex under investigation with the 2ylh target protein have been conducted in order to check the biological activity of the complex.

Research paper thumbnail of Infrared and Raman spectra, conformational stability, structural parameters, ab initio calculations and vibrational assignments of aminodifluorophosphine

Journal of Molecular Structure, 2008

Infrared spectra (4000–50 cm−1) have been recorded for three isotopomers of aminodifluorophosphin... more Infrared spectra (4000–50 cm−1) have been recorded for three isotopomers of aminodifluorophosphine, H2NPF2, H215NPF2 and D2NPF2, of the gases. The Raman spectra of all three molecules were recorded of the liquids. To support the vibrational assignment MP2(full) ab initio calculations with the 6-31G(d) basis set were carried out to predict the fundamental vibrational frequencies, infrared intensities, Raman activities, depolarization values and infrared band contours. Additional ab initio calculations employing a variety of basis sets with and without diffuse functions have been used to predict the conformational stability, structural parameters and centrifugal distortion constants. These predictions are compared to previously reported experimental values when available. The adjusted r0 structural parameters have been obtained by systematically fitting the MP2(full)/6-311+G(d) predicted values with the previously reported rotational constants for five isotopomers obtained from the mi...

Research paper thumbnail of Synthesis and Quantum Chemical Studies on the Tautomeric Structures of New Thiazole and Thiadiazine Derivatives

Current Organic Synthesis, 2016

Research paper thumbnail of A Facile Access and Computational Studies of Some New 4,5'-Bipyrazole Derivatives

Research paper thumbnail of Conformational stability, ro structural parameters, ab initio calculations, and vibrational assignment for cyanocyclopentane

Vibrational Spectroscopy, 2010

Research paper thumbnail of Conformational Stability, ro Structural Parameters, Ab Initio Calculations, and Vibrational Assignment for Fluorocyclopentane

The Journal of Physical Chemistry a, 2009

Research paper thumbnail of Conformational Stability from Variable-Temperature Infrared Spectra of Krypton Solutions, Ab Initio Calculations, and ro Structural Parameters of Chlorocyclopentane

Structural …, 2003

(1.73 ± 0.18 kJ-mol −1 ) has been obtained with theaxialconformer the more stable form. It is est... more (1.73 ± 0.18 kJ-mol −1 ) has been obtained with theaxialconformer the more stable form. It is estimated that there is 67 ± 2% of the axial conformer present at ambient temperature. Convincing spectroscopic evidence shows that a significant percentage of the chlorocyclopentane ...

Research paper thumbnail of Theoretical and Experimental Study on the Effect of End Chain Length on Ultraviolet Absorption Behavior and Photostability of Alkoxy Benzoate Based Liquid Crystals

Oriental Journal of Chemistry

Research paper thumbnail of Synthesis of some novel antioxidant and anticorrosive additives for Egyptian gasoline motor oils

Ghada Elbana, 2011

2-Methyl-benzo[d][1,3]oxazin-4-one (1) was used as a key intermediate for the synthesis of differ... more 2-Methyl-benzo[d][1,3]oxazin-4-one (1) was used as a key intermediate for the synthesis of different benzoxazinone and quinazolinone derivatives. In order to evaluate the applicability of the synthesised benzoxazinones and quinazolinones as antioxidant additives for lube oil, these antioxidant additives decomposed the alkyl peroxide radicals and/or alkyl hydrogen peroxides to produce esters, ketone and hydroxy compounds rather than carboxylic acids. The compounds that showed antioxidant efficiency were tested as corrosion inhibitors using three types of metals: Cu, Al and Fe.

Research paper thumbnail of Conformational Stability, r0 Structural Parameters, Ab Initio Calculations, and Vibrational Assignment for Fluorocyclopentane

J Phys Chem a, 2009

The infrared spectra (3200-50 cm-1) of the gas and solid and the Raman spectrum (3200-30 cm-1) of... more The infrared spectra (3200-50 cm-1) of the gas and solid and the Raman spectrum (3200-30 cm-1) of liquid and solid fluorocyclopentane, c-C5H9F, have been recorded. Additionally the infrared spectra (3200-400 cm-1) of liquid xenon solutions have been recorded at -65 and -95 °C. In all of the physical states, only the twisted C1 conformer was detected. Ab initio calculations utilizing various basis sets up to MP2(full)/6-311+G(2df,2pd) with and without diffuse functions have been used to predict the conformational stabilities. These calculations predict only the twisted C1 conformer as the stable form. The two envelope (Cs symmetry) forms with axial and equatorial structures were predicted to be first order saddle points with average higher energies of 75 ± 33 and 683 ± 44 cm-1, respectively, from the C1 conformer but lower energies of 2442 and 1812 cm-1, respectively, than the planar form by MP2 calculations. Similar values were obtained from the corresponding density functional theory calculations by the B3LYP method. A complete vibrational assignment is given for the twisted (C1) conformer which is supported by normal coordinate calculations with scaled force constants from MP2(full)/6-31G(d) calculations. The adjusted r0 structural parameters have been obtained by systematically fitting the MP2(full)/6-311+G(d,p) predicted values with the rotational constants obtained from a microwave study. The determined heavy atom r0 distances in Å are (C1C2) = 1.531(3), (C1C3) = 1.519(3), (C2C4) = 1.553(3), (C3C5) = 1.533(3), (C4C5) = 1.540(3), and (C1F6) = 1.411(3) and the angles in degrees are ∠C3C1C2 = 105.5(5), ∠C1C2C4 = 106.2(5), ∠C1C3C5 = 102.9(5), ∠F6C1C2 = 108.9(5), and ∠F6C1C3 = 107.6(5) with a dihedral angle ∠C2C4C5C3 = 25.3(3). These experimental and theoretical results are compared to the corresponding quantities of some similar molecules.

Research paper thumbnail of Vibrational spectra, r 0 structural parameters, barriers to internal rotation, and ab initio calculations of ClCH 2SiH 3, Cl 2CHSiH 3, ClCH 2SiF 3 and Cl 2CHSiF 3

Research paper thumbnail of Lornoxicam & Tenoxicam Drugs as Green Corrosion Inhibitors for Carbon Steel in 1 M H 2 SO 4 Solution

Inhibition performance of Lornoxicam & Tenoxicam against corrosion of carbon steel in 1 M H2SO4 s... more Inhibition performance of Lornoxicam & Tenoxicam against corrosion of carbon steel in 1 M H2SO4 solutions was investigated by weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements. The inhibition efficiency increased with increasing inhibitor's concentration, but decreased with increase in temperature. Potentiodynamic polarization curves showed that, the inhibitors were of mixed type. The apparent activation energy (E-a*) and other thermodynamic parameters for the corrosion process have also been calculated and discussed. The inhibition of carbon steel corrosion is due to the adsorption of the inhibitor molecules on the surface, which follows Temkin adsorption isotherm. The mechanism of inhibition was discussed in the light of the chemical structure of the undertaken inhibitors.

Research paper thumbnail of Theoretical Study of the Tautomeric Preference and Self Association Processes of 2-Pyrrolidinone

Relative tautomerization energies, dipole moments for the tautomers of 2-pyrrolidinone was studie... more Relative tautomerization energies, dipole moments for the tautomers of 2-pyrrolidinone was studied by quantum-chemical calculations, using the B3LYP level of calculation with the 6-311G(d,p) basis set in the gas phase with full geometry optimization. Entropies, enthalpies and Gibbs free energies for the tautomerization process of 2-pyrrolidinone was obtained using the RHF/6-31G(d) level of computation. The calculations showed that, the Keto form is the most stable form in the gas phase. The entropy effect on the Gibbs free energy change of the tautomerization process 2-pyrrolidinone is found to be very small, and has practically no significance for the tautomeric equilibria of the 2-pyrrolidinone. The enthalpic term is dominant in the determination of the equilibrium constant. The ability to form dimer, trimer and tetramer was investigated concerning the energetical changes; dipole moments using the RHF/6-31Gd level of computation. The thermodynamic parameters at different temperatu...

Research paper thumbnail of Synthesis, Cytotoxicity Evaluation, DFT Molecular Modeling Studies and Quantitative Structure Activity Relationship of Novel 1,8-Naphthyridines

American Journal of Organic Chemistry, 2012

Research paper thumbnail of Conformational Stability from Variable Temperature FT-IR Spectra of Krypton Solutions, r 0 Structural Parameters, Vibrational Assignment, and a b Initio Calculations of 4-Fluoro-1-butene

The Journal of Physical Chemistry A, 2008

The infrared spectra of gaseous and variable-temperature liquid xenon solutions of pyrrolidine ha... more The infrared spectra of gaseous and variable-temperature liquid xenon solutions of pyrrolidine have been recorded. The enthalpy difference has been determined to be 109 ± 11 cm(-1) (1.30 ± 0.13 kJ mol(-1)) with the envelope-equatorial conformer more stable than the twist form with 37 ± 3% present at ambient temperature. Ab initio calculations utilizing various basis sets up to MP2(full)/aug-cc-pVTZ have been used to predict the conformational stabilities, energy at the equatorial-axial saddle point, and barriers to planarity. From previously reported microwave rotational constants along with MP2(full)/6-311+G(d,p) predicted structural values, adjusted r(0) parameters have been obtained for both conformers. Heavy atom distances (Å) of equatorial[twist] conformer are as follows: N(1)-C(2) = 1.469(3)[1.476(3)], N(1)-C(3) = 1.469(3)[1.479(3)], C(2)-C(4) = 1.541(3)[1.556(3)], C(3)-C(5) = 1.541(3)[1.544(3)], C(4)-C(5) = 1.556(3)[1.543(3)]; and angles (deg)∠N(1)C(2)C(4) = 102.5(5)[107.6(5)], ∠N(1)C(3)C(5) = 102.5(5)[105.4(5)], ∠C(2)C(4)C(5) = 104.3(5)[104.6(5)], ∠C(3)C(5)C(4) = 104.3(5)[103.7(5)], ∠C(2)N(1)C(3) = 104.1(5)[103.9(5)], τC(2)C(4)C(5)C(3) = 0.0(5)[13.5(5)]. A complete vibrational assignment is proposed for both conformers.

Research paper thumbnail of Conformational stability of chlorocyclohexane from temperature-dependent FT-IR spectra of xenon solutions, r 0 structural parameters, and vibrational assignment

Structural Chemistry, 2008

Research paper thumbnail of Vibrational spectrum, conformational stability, structural parameters and ab initio calculations of dimethylaminodifluorophosphine

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2008

From analysis of the infrared and Raman spectra along with support from the ab initio predictions... more From analysis of the infrared and Raman spectra along with support from the ab initio predictions it is concluded that there is only one stable conformer of dimethylaminodifluorophosphine, (CH(3))(2)NPF(2), in the gaseous and liquid phases which has a planar PNC(2) moiety with C(s) symmetry. The adjusted r(0) structural parameters have been obtained by combining the MP2(full)/6-311+G(d) predicted values with the previous reported rotational constants for four isotopomers obtained from previously reported microwave studies. The difference in the two NC distances is 0.002A whereas, these two parameters were previously assumed to have the same values from the microwave and electron diffraction studies but a reported difference of 0.025A from the structural parameters of the crystal. The adjusted r(0) heavy atom distances and angles are: r(PF)=1.593(3); r(NP)=1.654(3); r(NC(i))=1.455(3); r(NC(o))=1.453(3) A; angleFPF=93.5(5); angleNPF=100.8(5); angleCNC=116.0(5); angleC(i)NP=124.1(5); angleC(o)NP=120.0 degrees . The planar bonding around the nitrogen atom is consistent with the previously reported structural information from the microwave study but differs from the slightly pyramidal bonding obtained in the electron diffraction investigation. To support the vibrational assignment MP2(full) ab initio calculations with the 6-31G(d) basis set were carried out to predict the fundamental vibrational frequencies, infrared intensities, Raman activities, depolarization values, infrared band contours, and centrifugal distortion constants. Vibrational assignments are given for (CH(3))(2)NPF(2) and (CD(3))(2)NPF(2) and comparisons are made with the predicted intensities, frequencies and centrifugal distortion constants. Frequencies of some of the lattice modes are reported from both the infrared and Raman spectra with suggested assignments based on the factor group symmetry of the crystal of D(2h)(16) (Pnma) with four molecules per primitive cell. These results are compared to the corresponding quantities of some similar molecules.

Research paper thumbnail of Conformational stability of cyclobutanol from temperature dependent infrared spectra of xenon solutions, r0 structural parameters, ab initio calculations and vibrational assignment

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2008

Variable temperature (-55 to -100 degrees C) studies of the infrared spectra (4000-400 cm(-1)) of... more Variable temperature (-55 to -100 degrees C) studies of the infrared spectra (4000-400 cm(-1)) of cyclobutanol, c-C4H7OH dissolved in liquid xenon have been carried out. The infrared spectrum (4000-100 cm(-1)) of the gas has also been recorded. From these data two of the four possible stable conformers have been confidently identified and their order of stabilities has been experimentally determined where the first indicator is for the position of attachment of the hydroxyl group on the bent cyclobutyl ring (Eq=equatorial or Ax=axial) and the second one (t=trans, g=gauche) is the relative position of the hydroxyl rotor, i.e. rotation around the ring C-O bond. The enthalpy difference between the most stable Eq-t conformer and the second most stable rotamer, Eq-g, has been determined to be 200+/-50 cm(-1) (2.39+/-0.60 kJ/mol). This experimentally determined order is consistent with the order of stability predicted by ab initio calculations Eq-t>Eq-g>Ax-g>Ax-t. Evidence was obtained for the third conformer Ax-g which is predicted by ab initio calculations to be less stable by more than 650cm(-1) than the Eq-t form. The percentage of each conformer at ambient temperature is estimated to be Eq-t (50%), Eq-g (47%) and Ax-g (3%). The conformational stabilities, harmonic force fields, infrared intensities, Raman activities, depolarization ratios and vibrational frequencies have been obtained for all of the conformers from MP2(full)/6-31G(d) ab initio calculations. The optimized geometries and conformational stabilities have been obtained from ab initio calculations utilizing several different basis sets up to MP2(full)/aug-cc-pVTZ and from density functional theory calculations by the B3LYP method. By utilizing previously reported microwave rotational constants for the Eq-t conformer combined with ab initio MP2(full)/6-311+G(d,p) predicted structural values, adjusted r0 parameters have been obtained. The determined heavy atom structural parameters for the Eq-t conformer are: the distances C1-C4=1.547(5) angstroms, C4-C6=1.552(5)angstroms, C-O=1.416(5) angstroms and angles angleC6C4C1=86.6(5) degrees , angleC4C1C5=88.9(5) degrees and angleC6C5C1C4=22.8(5) degrees . The results are discussed and compared to the corresponding properties of some similar molecules.