Synthesis and spectroscopic investigation of (acetylamino)pyridines

2009 ◽  
Vol 74 (9) ◽  
pp. 1295-1308 ◽  
Author(s):  
Atanas G. Chapkanov ◽  
Sonya Y. Zareva ◽  
Rositsa Nikolova ◽  
Elena Trendafilova
Keyword(s):  
Electronic Structure ◽  
Ir Spectroscopy ◽  
Condensed Phase ◽  
Quantum Chemical ◽  
The Self ◽  
Basis Set ◽  
B3lyp Level ◽  
Vibrational Characteristics ◽  
Self Association ◽  
Polarized Ir Spectroscopy

The self-association of 2- and 3-(acetylamino)pyridines in a condensed phase was investigated by conventional and linear-polarized IR spectroscopy. Interpretation of spectra of the monomer and associated forms was carried out by the reducing-difference procedure. Theoretical quantum chemical calculations at the B3LYP level of theory and with 6-31±G** basis set were performed in order to obtain the electronic structure and vibrational characteristics of both compounds.

scholarly journals Solid-state linear polarized IR-spectroscopy of croconic and rhodizonic acids

2008 ◽  
Vol 6 (3) ◽  
pp. 393-399 ◽  
Author(s):  
Tsonko Kolev ◽  
Bojidarka Koleva ◽  
Michael Spiteller
Keyword(s):  
Solid State ◽  
Ir Spectroscopy ◽  
Quantum Chemical Calculations ◽  
Quantum Chemical ◽  
Vibrational Analysis ◽  
Basis Set ◽  
Experimental Ir ◽  
Vibrational Assignments ◽  
Neutral Compounds ◽  
Polarized Ir Spectroscopy

AbstractThe applications of linear-polarized IR-spectroscopy to oriented colloid suspensions in a nematic host are demonstrated with croconic and rhodizonic acids. The experimental IR vibrational assignments of the solid-state of both neutral compounds are presented. Assignments are supported by theoretical quantum chemical calculations and vibrational analysis at the DFT level of theoretical approximation with the 6-311++G** basis set.

Analysis of the Self-Association of Aliphatic Alcohols Using Fourier Transform Infrared (FT-IR) Spectroscopy

2013 ◽  
Vol 52 (40) ◽  
pp. 14456-14462 ◽  
Author(s):  
John T. Reilly ◽  
Arun Thomas ◽  
Aileen R. Gibson ◽  
Chi Y. Luebehusen ◽  
Marc D. Donohue
Keyword(s):  
Fourier Transform ◽  
Ir Spectroscopy ◽  
Fourier Transform Infrared ◽  
Aliphatic Alcohols ◽  
The Self ◽  
Ft Ir ◽  
Self Association ◽  
Ft Ir Spectroscopy

Benchmarking Electronic Structure Methods for Accurate Fixed-Charge Electrostatic Models

2019 ◽  
Author(s):  
Alex Zhou ◽  
Michael Schauperl ◽  
Paul Nerenberg
Keyword(s):  
Electronic Structure ◽  
Gas Phase ◽  
Condensed Phase ◽  
Force Fields ◽  
Dipole Moments ◽  
Fixed Charge ◽  
Basis Set ◽  
Atomic Charges ◽  
Molecular Dipole ◽  
Partial Atomic Charges

<p>The accuracy of classical molecular mechanics (MM) force fields used for condensed phase molecular simulations depends strongly on the accuracy of modeling nonbonded interactions between atoms, such as electrostatic interactions. Some popular fixed-charge MM force fields use partial atomic charges derived from gas phase electronic structure calculations using the Hartree-Fock method with the relatively small 6-31G* basis set (HF/6-31G*). It is generally believed that HF/6-31G* generates fortuitously overpolarized electron distributions, as would be expected in the higher dielectric environment of the condensed phase. Using a benchmark set of 47 molecules we show that HF/6-31G* overpolarizes molecules by just under 10% on average with respect to experimental gas phase dipole moments. The overpolarization of this method/basis set combination varies significantly though and, in some cases, even leads to molecular dipole moments that are lower than experimental gas phase measurements. We further demonstrate that using computationally inexpensive density functional theory (DFT) methods, together with appropriate augmented basis sets and a continuum solvent model, can yield molecular dipole moments that are both more strongly and more uniformly overpolarized. These data suggest that these methods – or ones similar to them – should be adopted for the derivation of accurate partial atomic charges for next-generation MM force fields.<br></p>

scholarly journals Novel organic material with potential NLO application - electronic and spectroscopic properties

2008 ◽  
Vol 6 (4) ◽  
pp. 592-599 ◽  
Author(s):  
B.B. Koleva ◽  
T. Kolev ◽  
R. Nikolova ◽  
Y. Zagraniarsky ◽  
M. Spiteller
Keyword(s):  
Optical Properties ◽  
Electronic Structure ◽  
Ir Spectroscopy ◽  
Ab Initio ◽  
Organic Material ◽  
Spectroscopic Properties ◽  
Thermal Methods ◽  
Polarized Ir Spectroscopy ◽  
Cosy Nmr ◽  
Ab Initio And Dft

AbstractNovel dicyanoisophorone derivative, (E)-2-(3-(4-aminostyryl)-5,5-dimethylcyclohex-2-enylidene)malononitrile, is synthesized and its structure elucidated by means of conventional and linear polarized IR-spectroscopy of oriented colloids in nematic host, 1H, 13C, 1H, 1H-COSY NMR, HPLC tandem ESI MS-MS spectrometry, UV-VIS and thermal methods. Ab initio and DFT level of theory are used to theoretically obtain the electronic structure and optical properties, both in ground and exited state, of the compound.

Benchmarking Electronic Structure Methods for Accurate Fixed-Charge Electrostatic Models

2019 ◽  
Author(s):  
Alex Zhou ◽  
Michael Schauperl ◽  
Paul Nerenberg
Keyword(s):  
Electronic Structure ◽  
Gas Phase ◽  
Condensed Phase ◽  
Force Fields ◽  
Dipole Moments ◽  
Fixed Charge ◽  
Basis Set ◽  
Atomic Charges ◽  
Molecular Dipole ◽  
Partial Atomic Charges

<p>The accuracy of classical molecular mechanics (MM) force fields used for condensed phase molecular simulations depends strongly on the accuracy of modeling nonbonded interactions between atoms, such as electrostatic interactions. Some popular fixed-charge MM force fields use partial atomic charges derived from gas phase electronic structure calculations using the Hartree-Fock method with the relatively small 6-31G* basis set (HF/6-31G*). It is generally believed that HF/6-31G* generates fortuitously overpolarized electron distributions, as would be expected in the higher dielectric environment of the condensed phase. Using a benchmark set of 47 molecules we show that HF/6-31G* overpolarizes molecules by just under 10% on average with respect to experimental gas phase dipole moments. The overpolarization of this method/basis set combination varies significantly though and, in some cases, even leads to molecular dipole moments that are lower than experimental gas phase measurements. We further demonstrate that using computationally inexpensive density functional theory (DFT) methods, together with appropriate augmented basis sets and a continuum solvent model, can yield molecular dipole moments that are both more strongly and more uniformly overpolarized. These data suggest that these methods – or ones similar to them – should be adopted for the derivation of accurate partial atomic charges for next-generation MM force fields.<br></p>

Quantum-Chemical Insight Into Mechanism of Combined Intra-Intermolecular Cycloaddition

2004 ◽  
Vol 69 (1) ◽  
pp. 231-241 ◽  
Author(s):  
Petr Kulhánek ◽  
Milan Potáček ◽  
Jaroslav Koča
Keyword(s):  
Experimental Data ◽  
Reaction Mechanisms ◽  
Quantum Chemical ◽  
Activation Barrier ◽  
Probable Mechanism ◽  
Basis Set ◽  
Rate Determining Step ◽  
B3lyp Level ◽  
Opposite Sequence ◽  
Insight Into

Two different reaction mechanisms of a mixed criss-cross cycloaddition with opposite sequence of reaction steps, intra-intermolecular and inter-intramolecular, were explored by quantum-chemical calculations at the MP2 and B3LYP levels of theory and with cc-pVDZ basis set. It was found that the rate-determining step in the both mechanisms is the first step regardless of the mechanism. The Gibbs activation barrier of the intramolecular step of the intra-intermolecular sequence is by 10.4 kcal mol-1 lower than that of the intermolecular step of the inter-intramolecular sequence at the MP2 level of theory and almost the same at the B3LYP level of theory. This together with known experimental data confirms that the intra-intermolecular sequence is the most probable mechanism.

Benchmarking Electronic Structure Methods for Accurate Fixed-Charge Electrostatic Models

2019 ◽  
Author(s):  
Alex Zhou ◽  
Michael Schauperl ◽  
Paul Nerenberg
Keyword(s):  
Electronic Structure ◽  
Gas Phase ◽  
Condensed Phase ◽  
Force Fields ◽  
Dipole Moments ◽  
Fixed Charge ◽  
Basis Set ◽  
Atomic Charges ◽  
Molecular Dipole ◽  
Partial Atomic Charges

<div><div><div><p>The accuracy of classical molecular mechanics (MM) force fields used for condensed phase molecular simulations depends strongly on the accuracy of modeling nonbonded interactions between atoms, such as electrostatic interactions. Some popular fixed-charge MM force fields use partial atomic charges derived from gas phase electronic structure calculations using the Hartree-Fock method with the relatively small 6-31G* basis set (HF/6-31G*). It is generally believed that HF/6-31G* generates fortuitously overpolarized electron distributions, as would be expected in the higher dielectric environment of the condensed phase. Using a benchmark set of 47 molecules, we show that HF/6-31G* does not uniformly overpolarize molecules and in some cases even leads to molecular dipole moments that are lower than experimental gas phase measurements. We further demonstrate that using computationally inexpensive density functional theory (DFT) methods, together with appropriate augmented basis sets and a continuum solvent model, can yield molecular dipole moments that are both more strongly and more uniformly overpolarized. These data suggest that these methods – or ones similar to them – should be adopted for the derivation of accurate partial atomic charges for next-generation MM force fields.</p></div></div></div>

Performance of Electronic Structure Methods for the Description of Hückel-Möbius Interconversions in Extended π-Systems

2019 ◽  
Author(s):  
Tatiana Woller ◽  
Ambar Banerjee ◽  
Nitai Sylvetsky ◽  
Xavier Deraet ◽  
Frank De Proft ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Basis Set ◽  
Dft Methods ◽  
Molecular Switching ◽  
Wide Range ◽  
Electronic Structure Methods ◽  
Explicitly Correlated ◽  
Relative Errors ◽  
The Stability ◽  
Basis Set Expansion

<p>Expanded porphyrins provide a versatile route to molecular switching devices due to their ability to shift between several π-conjugation topologies encoding distinct properties. Taking into account its size and huge conformational flexibility, DFT remains the workhorse for modeling such extended macrocycles. Nevertheless, the stability of Hückel and Möbius conformers depends on a complex interplay of different factors, such as hydrogen bonding, p···p stacking, steric effects, ring strain and electron delocalization. As a consequence, the selection of an exchange-correlation functional for describing the energy profile of topological switches is very difficult. For these reasons, we have examined the performance of a variety of wavefunction methods and density functionals for describing the thermochemistry and kinetics of topology interconversions across a wide range of macrocycles. Especially for hexa- and heptaphyrins, the Möbius structures have a pronouncedly stronger degree of static correlation than the Hückel and figure-eight structures, and as a result the relative energies of singly-twisted structures are a challenging test for electronic structure methods. Comparison of limited orbital space full CI calculations with CCSD(T) calculations within the same active spaces shows that post-CCSD(T) correlation contributions to relative energies are very minor. At the same time, relative energies are weakly sensitive to further basis set expansion, as proven by the minor energy differences between MP2/cc-pVDZ and explicitly correlated MP2-F12/cc-pVDZ-F12 calculations. Hence, our CCSD(T) reference values are reasonably well-converged in both 1-particle and n-particle spaces. While conventional MP2 and MP3 yield very poor results, SCS-MP2 and particularly SOS-MP2 and SCS-MP3 agree to better than 1 kcal mol<sup>-1</sup> with the CCSD(T) relative energies. Regarding DFT methods, only M06-2X provides relative errors close to chemical accuracy with a RMSD of 1.2 kcal mol<sup>-1</sup>. While the original DSD-PBEP86 double hybrid performs fairly poorly for these extended p-systems, the errors drop down to 2 kcal mol<sup>-1</sup> for the revised revDSD-PBEP86-NL, again showing that same-spin MP2-like correlation has a detrimental impact on performance like the SOS-MP2 results. </p>

The Nature of Chemisorbed CO2 in Zeolite A

2019 ◽  
Author(s):  
Przemyslaw Rzepka ◽  
Zoltán Bacsik ◽  
Andrew J. Pell ◽  
Niklas Hedin ◽  
Aleksander Jaworski
Keyword(s):  
Solid State ◽  
Ir Spectroscopy ◽  
Quantum Chemical Calculations ◽  
Quantum Chemical ◽  
Surface Coverage ◽  
Gas Mixtures ◽  
Mas Nmr ◽  
Significant Fraction ◽  
Zeolite A

Formation of CO<sub>3</sub><sup>2-</sup> and HCO<sub>3</sub><sup>-</sup> species without participation of the framework oxygen atoms upon chemisorption of CO<sub>2</sub> in zeolite |Na<sub>12</sub>|-A is revealed. The transfer of O and H atoms is very likely to have proceeded via the involvement of residual H<sub>2</sub>O or acid groups. A combined study by solid-state <sup>13</sup>C MAS NMR, quantum chemical calculations, and <i>in situ</i> IR spectroscopy showed that the chemisorption mainly occurred by the formation of HCO<sub>3</sub><sup>-</sup>. However, at a low surface coverage of physisorbed and acidic CO<sub>2</sub>, a significant fraction of the HCO<sub>3</sub><sup>-</sup> was deprotonated and transformed into CO<sub>3</sub><sup>2-</sup>. We expect that similar chemisorption of CO<sub>2</sub> would occur for low-silica zeolites and other basic silicates of interest for the capture of CO<sub>2</sub> from gas mixtures.

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