scholarly journals Scaled quantum chemical studies of the structural and vibrational spectra of acetyl coumarin

2006 ◽  
Vol 4 (4) ◽  
Author(s):  
Khaled Bahgat
Keyword(s):  
Density Functional ◽  
Solid Phase ◽  
Normal Modes ◽  
Basis Sets ◽  
Functional Theory ◽  
Hartree Fock ◽  
Full Structure ◽  
Chemical Studies ◽  
Quantum Chemical Studies ◽  
Ft Ir

AbstractThe solid phase FT-IR and FR-Raman spectra of acetyl coumarin have been recorded in the regions 4000–50 cm−1. The spectra were interpreted with the aid of normal coordinate analysis following full structure optimization and force field calculations based on density functional theory (DFT) and Hartree-Fock (HF) at 6–31G* and 6–311++G** basis sets. The resulting force fields were transformed to internal coordinates, the calculated vibrational frequencies and normal modes were utilized in the assignment of the observed vibrational fundamentals. The measured spectral data were used to refine the vibrational force constants by means of a small number of scaling factors.

Nontemplate synthesis, characterization and theoretical study of tetraazamacrocycles

2012 ◽  
Vol 23 (1) ◽  
pp. 121-127
Author(s):  
İbrahim Șen ◽  
Cem Burak Yildiz ◽  
Akın Azizoğlu
Keyword(s):  
Density Functional ◽  
Basis Sets ◽  
Frontier Molecular Orbital ◽  
Spectroscopic Techniques ◽  
Functional Theory ◽  
Hartree Fock ◽  
H Nmr ◽  
Ft Ir ◽  
Molecular Electrostatic Potential Maps ◽  
C Nmr

Abstract The syntheses of new tetraaza macrocyclic compounds of variable ring sizes by non-template methods and their characterization with the help of elemental analysis and spectroscopic techniques (FT-IR, 1H-NMR, and 13C-NMR) have been reported in detail. The vibrational frequencies determined experimentally are compared with those obtained theoretically from density functional theory (DFT) and Hartree-Fock (HF) calculations. The comparisons between the experimental and theoretical results indicate that B3LYP level with both the 3-21G(d) and 6-31G+(d,p) basis sets is able to provide satisfactory results for predicting IR properties. The frontier molecular orbital diagrams and molecular electrostatic potential maps of title compounds have been also calculated and visualized at the B3LYP/6-31G+(d,p) level of theory.

scholarly journals Vibrational spectroscopic and Hirshfeld surface analysis of N,N'-(azanediylbis(2,1-phenylene))bis(2-chloropropanamide)

2019 ◽  
Vol 10 (4) ◽  
pp. 386-402
Author(s):  
Aysegul Suzan Polat ◽  
Ilkay Gumus ◽  
Hakan Arslan
Keyword(s):  
Surface Analysis ◽  
Intermolecular Interactions ◽  
Density Functional ◽  
Solid Phase ◽  
Hirshfeld Surface ◽  
Hirshfeld Surface Analysis ◽  
Basis Sets ◽  
Hartree Fock ◽  
Ft Ir ◽  
Ir And Raman

The title molecule, N,N'-(azanediylbis(2,1-phenylene))bis(2-chloropropanamide) (LNNN) was synthesized and characterized by means of Hirshfeld surface analysis and vibrational (FT-IR and RAMAN) studies. Ab-initio Hartree-Fock (HF) and density functional theory (DFT; BLYP, B3LYP, B3PW91 and mPW1PW91) calculations were accomplished using 6-31G(d,p) and 6-311G(d,p) basis sets. The comparison of calculated bond lengths and angles with X-ray crystal structure shows sufficient agreement. The solid phase FT-IR and FT-RAMAN spectra of LNNN have been recorded in the regions 4000-525 cm-1 and 4000-50 cm-1, respectively. A comparative analysis between the calculated and experimental vibrational frequencies was carried out and significant bands were assigned. The results indicated a good correlation between experimental and theoretical IR and RAMAN frequencies. A detailed analysis of the intermolecular interactions via Hirshfeld surface analysis and fingerprint plots revealed that supramolecular structure of the LNNN is stabilized mainly by the formation of H···H, C···H, Cl···H ve O···H  intermolecular interactions.

scholarly journals Molecular bending as a vital step toward transforming planar PAHs to fullerenes and tubular structures

2020 ◽  
Vol 644 ◽  
pp. A146
Author(s):  
Tao Chen ◽  
Yang Wang
Keyword(s):  
Density Functional ◽  
Intermolecular Forces ◽  
Molecular Structures ◽  
Intrinsic Reaction Coordinate ◽  
Functional Theory ◽  
B3lyp Method ◽  
Polycyclic Aromatic ◽  
Chemical Studies ◽  
Quantum Chemical Studies ◽  
Hybrid Density Functional

Context. Polycyclic aromatic hydrocarbons (PAHs) and fullerenes are the largest molecules found in the interstellar medium (ISM). They are abundant and widespread in various astronomical environments. However, the detailed connection between these two species is unknown; in particular, no quantum chemical studies have been performed. Aims. In this work, we investigate a vital step in transforming planar PAHs to fullerenes, that is, the tubulation processes of PAHs. Methods. We used density functional theory for this study. The molecular structures and vibrational frequencies were calculated using the hybrid density functional B3LYP method. To better describe intermolecular forces, we considered Grimme’s dispersion correction in the calculations for this work. Intrinsic reaction coordinate calculations were also performed to confirm that the transition state structures are connected to their corresponding local potential energy surface minima. Results. As expected, we find that it is easier to bend a molecule as it gets longer, whereas it is harder to bend the molecule if it gets “wider” (i.e., with more rows of benzene rings). The change of multiplicity slightly alters the bending energies, while (a complete) dehydrogenation alleviates the bending barrier significantly and facilitates the formation of pentagons, which may act as an indispensable step in the formation of fullerenes in the ISM.

THE ORIGIN OF THE ROTATIONAL BARRIER IN DIMETHYL ETHER AND DIMETHYL SULFIDE: A THEORETICAL STUDY

2007 ◽  
Vol 06 (03) ◽  
pp. 421-434 ◽  
Author(s):  
JÍMENEZ-FABIAN ◽  
A. F. JALBOUT
Keyword(s):  
Dimethyl Ether ◽  
Density Functional ◽  
Dimethyl Sulfide ◽  
Nbo Analysis ◽  
Rotational Barrier ◽  
Basis Sets ◽  
Functional Theory ◽  
Hartree Fock ◽  
Torsional Potential ◽  
Methyl Rotation

The torsional potential function for methyl rotation in dimethyl ether (DME) and dimethyl sulfide (DMS) has been determined by utilizing ab initio (Hartree–Fock and MP2) and density functional theory (B3LYP, B3P86, and B3PW91) methods along with several basis sets. Natural bond orbital (NBO) analysis was also applied to investigate the origin of the rotational barrier.

scholarly journals Quantum chemical studies on the molecular structure, spectroscopic and electronic properties of (6-Methoxy-2-oxo-2H-chromen-4-yl)-methyl pyrrolidine-1-carbodithioate

2016 ◽  
Vol 34 (4) ◽  
pp. 886-904 ◽  
Author(s):  
Meryem Evecen ◽  
Hasan Tanak
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Electronic Absorption Spectra ◽  
Chemical Shifts ◽  
Density Functional Theory Calculations ◽  
Molecular Geometry ◽  
Basis Set ◽  
Functional Theory ◽  
Hartree Fock ◽  
Chemical Studies

AbstractIn this paper, the molecular geometry, vibrational frequencies and chemical shifts of (6-Methoxy-2-oxo-2H-chromen-4-yl)methyl pyrrolidine-1-carbodithioate in the ground state have been calculated using the Hartree-Fock and density functional methods with the 6-311++G(d,p) basis set. To investigate the nonlinear optical properties of the title compound, the polarizability and the first hyperpolarizability were calculated. The conformational properties of the molecule have been determined by analyzing molecular energy properties. Using the time dependent density functional theory, electronic absorption spectra have been calculated. Frontier molecular orbitals, natural bond orbitals, natural atomic charges and thermodynamical parameters were also investigated by using the density functional theory calculations.

scholarly journals A Statistically Supported Antioxidant Activity DFT Benchmark—The Effects of Hartree–Fock Exchange and Basis Set Selection on Accuracy and Resources Uptake

Molecules ◽  
2021 ◽  
Vol 26 (16) ◽  
pp. 5058
Author(s):  
Maciej Spiegel ◽  
Andrzej Gamian ◽  
Zbigniew Sroka
Keyword(s):  
Density Functional ◽  
Optimal Level ◽  
Basis Set ◽  
Basis Sets ◽  
Linear Regression Models ◽  
Functional Theory ◽  
Hartree Fock ◽  
Diffuse Function ◽  
Vertical Electron Affinity ◽  
High Level

Polyphenolic compounds are now widely studied using computational chemistry approaches, the most popular of which is Density Functional Theory. To ease this process, it is critical to identify the optimal level of theory in terms of both accuracy and resource usage—a challenge we tackle in this study. Eleven DFT functionals with varied Hartree–Fock exchange values, both global and range-separated hybrids, were combined with 14 differently augmented basis sets to calculate the reactivity indices of caffeic acid, a phenolic acid representative, and compare them to experimental data or a high-level of theory outcome. Aside from the main course, a validation of the widely used Janak’s theorem in the establishment of vertical ionization potential and vertical electron affinity was evaluated. To investigate what influences the values of the properties under consideration, linear regression models were developed and thoroughly discussed. The results were utilized to compute the scores, which let us determine the best and worst combinations and make broad suggestions on the final option. The study demonstrates that M06–2X/6–311G(d,p) is the best fit for such research, and, curiously, it is not necessarily essential to include a diffuse function to produce satisfactory results.

Conformational stability, barriers to internal rotations, and normal coordinate analysis of acetone and its2H-isotopomers

2016 ◽  
Vol 94 (10) ◽  
pp. 818-826 ◽  
Author(s):  
Mahboobeh Gholamhoseinpour ◽  
Sayyed Faramarz Tayyari ◽  
Saeedreza Emamian
Keyword(s):  
Density Functional ◽  
Conformational Stability ◽  
Normal Modes ◽  
Normal Coordinate Analysis ◽  
Basis Set ◽  
Basis Sets ◽  
Potential Energy Distribution ◽  
Normal Coordinate ◽  
Functional Theory ◽  
Vibrational Bands

Molecular structure and vibrational spectra of acetone, acetone-d3, and acetone-d6were investigated by means of ab initio and density functional theory (DFT) calculations. The harmonic and anharmonic vibrational frequencies of the acetone isotopomers were calculated at the B3LYP (using the 6–311++G(3df,3pd) basis set) and B2PLYP (using the 6–31+(2d,p) and 6–311G(2df,p) basis sets) levels. The calculated frequencies and the Raman and infrared (IR) intensities were compared with the experimental results. Excellent agreement between calculated and observed vibrational wavenumbers was obtained. Additionally, a normal coordinate analysis (NCA) was also done by using the normal mode eigenvectors obtained at the B3LYP/6–311++G(3df,3pd) level. All fundamental vibrational bands were assigned to the normal modes with the aid of the potential energy distribution (PED) values obtained from normal coordinate calculations. To study the internal rotation of CH3groups, single CH3rotation and synchronous rotations of both CH3groups (clockwise–clockwise and clockwise–counterclockwise) were analyzed using the MP2/6–311++G(3df,2pd) and B3LYP/6–311++G(3df,2pd) levels.

Interpretation of experimental IR spectra of (z)-4-(2- (acryloyloxy)ethoxy)-4-oxobut-2-enoic acid and its polymers

e-Polymers ◽  
2008 ◽  
Vol 8 (1) ◽  
Author(s):  
Chen Song ◽  
Xiaoyu Li
Keyword(s):  
Ir Spectra ◽  
Density Functional ◽  
Solid Phase ◽  
Enoic Acid ◽  
Field Calculation ◽  
Double Bonds ◽  
Absorption Bands ◽  
Experimental Ir ◽  
Functional Theory ◽  
Full Structure

AbstractThe solid phase FTIR spectra of (z)-4-(2-(acryloyloxy)ethoxy)-4-oxobut- 2-enoic acid (cis-AEOEA) and its polymers have been recorded in the regions 3500~500 cm-1, respectively. The IR spectra of cis-AEOEA was interpreted with the aid of normal coordinated analysis following full structure optimization and force field calculation based on density functional theory (DFT). Standard scaling factor was used to afford better correspondence between the calculated and experimental wavenumbers for the separation and unambiguous identification of observed IR spectra of cis-AEOEA, especially for C=C double bonds. The characteristic absorption bands of C=C are used for identifying the kind of C=C double bonds in cis-AEOEA’s polymers.

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