VIBRATIONAL SPECTROSCOPIC INVESTIGATION AND CONFORMATIONAL ANALYSIS OF 1-PENTYLAMINE: A COMPARATIVE DENSITY FUNCTIONAL STUDY

2010 ◽  
Vol 09 (03) ◽  
pp. 667-685 ◽  
Author(s):  
ÖZGÜR ALVER ◽  
CEMAL PARLAK
Keyword(s):  
Density Functional ◽  
Density Functional Method ◽  
Absolute Error ◽  
Functional Method ◽  
Basis Set ◽  
Functional Study ◽  
Stable Form ◽  
Water Solvent ◽  
B3lyp Method ◽  
Ft Ir

The possible stable conformers of 1-pentylamine (1-pa) molecule were experimentally and theoretically studied by FT-IR and Raman spectroscopy in the region of 4000–400 cm-1. The optimized geometric structures concerning the minimum on the potential energy surface were investigated by Becke-3–Lee–Yang–Parr (B3LYP) density functional method together with 6-31G(d) basis set. Based on the energy calculations, 10 possible rotamers of 1-pa (TT, TG, GT, GT1, GG1, GG2, GG3, GG4, GG5 and GG6; T and G denote trans and gauge, respectively) were proposed. Optimized energies of the possible conformers were obtained in the gas phase and within the chloroform, carbon tetrachloride, methanol and water solvent environments all of which have different polarities. Comparison between the experimental and theoretical results based on the correlation graphics and mean absolute error calculations presented in this study indicates that density functional B3LYP method is able to provide satisfactory results for predicting vibrational wavenumbers and TT isomer is the most stable form of 1-pa molecule.

scholarly journals Density functional theory study on the molecular structure of loganin

2011 ◽  
Vol 25 (6) ◽  
pp. 287-302 ◽  
Author(s):  
Anoop Kumar Pandey ◽  
Shamoon Ahmad Siddiqui ◽  
Apoorva Dwivedi ◽  
Kanwal Raj ◽  
Neeraj Misra
Keyword(s):  
Molecular Structure ◽  
Density Functional ◽  
Solid Phase ◽  
Density Functional Method ◽  
Functional Method ◽  
Basis Set ◽  
Equilibrium Geometry ◽  
B3lyp Method ◽  
Ft Ir ◽  
Detailed Interpretation

The computational Quantum Chemistry (QC) has been used for different types of problems, for example: structural biology, surface phenomena and liquid phase. In this paper we have employed the density functional method for the study of molecular structure of loganin. The equilibrium geometry, harmonic vibrational frequencies and infrared intensities were calculated by B3LYP/6-311G (d, p) method and basis set combinations. It was found that the optimized parameters obtained by the DFT/B3LYP method are very near to the experimental ones. A detailed conformational analysis was carried out. A detailed interpretation of the infrared spectra of loganin is also reported in the present work. The FT-IR spectra of loganin were recorded in solid phase. The thermodynamic calculations related to the title compound were also performed at B3LYP/6-311G (d, p) level of theory.

Vibrational Analysis of Trimethylphenyl Ammonium Chloride

2009 ◽  
Vol 64 (1-2) ◽  
pp. 127-131
Author(s):  
Halil Gökce ◽  
Semiha Bahçeli
Keyword(s):  
Ammonium Chloride ◽  
Density Functional ◽  
Density Functional Method ◽  
Vibrational Analysis ◽  
Functional Method ◽  
Vibrational Frequencies ◽  
Basis Set ◽  
Hartree Fock ◽  
B3lyp Method ◽  
Ft Ir

An FT-IR spectrum of trimethylphenyl ammonium chloride (TMPAC) has been recorded in the region 4000 - 400 cm−1. The optimized geometry and vibrational spectrum TMPAC in the ground state have been calculated by using ab initio Hartree-Fock (HF) calculations and the density functional method B3LYP with the 6-31G (d) basis set. The obtained vibrational frequencies and optimized geometric parameters (bond lengths and bond angles) were in very good agreement with the experimental data. The comparison of the observed and calculated results for the vibrational frequencies of TMPAC exhibited that the scaled B3LYP method is superior compared to the scaled HF method. Furthermore the calculated infrared and Raman intensities are also reported.

Vibrational spectroscopic and conformational studies of 1-(4-pyridyl)piperazine

2010 ◽  
Vol 64 (4) ◽  
Author(s):  
Özgür Alver ◽  
Mustafa Şenyel
Keyword(s):  
Density Functional ◽  
Structural Parameters ◽  
Density Functional Theory Method ◽  
Basis Set ◽  
Stable Form ◽  
Functional Theory ◽  
B3lyp Method ◽  
Ft Ir ◽  
Hybrid Density Functional ◽  
Ir And Raman

AbstractPossible stable conformers of the 1-(4-pyridyl)piperazine (1-4pypp) molecule were experimentally and theoretically studied by FT-IR and Raman spectroscopy. FT-IR and Raman spectra were recorded in the region of 4000–200 cm−1. Optimized geometric structures related to the minimum on the potential energy surface were investigated by the B3LYP hybrid density functional theory method using the 6-31G(d) basis set. Comparison of the experimental and theoretical results indicates that the density functional B3LYP method provides satisfactory results for the prediction of vibrational wavenumbers and structural parameters and equatorial-equatorial (e-e) isomer is supposed to be the most stable form of the 1–4pypp molecule.

Experimental and Computational Studies on Aminoguanidine Free Base, Monocation and Dication, Part II: Acid-Base Properties, Gas Phase Protonation Energies and Total Energies of Two Tautomers of the Free Base

1997 ◽  
Vol 52 (10) ◽  
pp. 1259-1272 ◽  
Author(s):  
Jere T. Koskinen ◽  
Mikko Koskinen ◽  
Ilpo Mutikainen ◽  
Pirkko Tilus ◽  
Berit Mannfors ◽  
...  
Keyword(s):  
Gas Phase ◽  
Density Functional ◽  
Density Functional Method ◽  
Functional Method ◽  
Basis Set ◽  
Stable Form ◽  
Free Base ◽  
Acid Base ◽  
Total Energies ◽  
The Difference

The structures and protonation energies of aminoguanidine and aminoguanidinium ion were obtained from quantum chemical calculations by using the density functional method B3-LYP and the standard basis set 6 -31 G(d ). The energy differences between the various forms of the two possible tautomers, the endiamine and the imidamide form, were investigated. The endiamine was found to be more stable than the most stable form of the imidamide by 5 kcal/mol in the gas phase. The proton affinity of am inoguanidine was found to be 241.4 kcal/mol (B3 -LYP/6 -31 G(d )) in the gas phase. The liquidation pKa2 for amininoguanidine and the guanidinium ion was determined to be 11.5 ± 0.1. The reference values for guanidine free base and the guanidinium ion are 235.7 kcal/mol and 13.6, respectively. The difference in the order of basicity in the gas phase and in aqueous solution between aminoguanidine and guanidine is discussed in terms of symmetry, resonance, delocalisation, rehybridisation of nitrogen atoms, and electrostatic repulsion.

scholarly journals Origin Invariant Full Optical Rotation Tensor in the Length Dipole Gauge without London Atomic Orbitals

2021 ◽  
Author(s):  
Marco Caricato
Keyword(s):  
Electron Correlation ◽  
Density Functional ◽  
Optical Rotation ◽  
Density Functional Method ◽  
Functional Method ◽  
Basis Set ◽  
Rotation Tensor ◽  
Atomic Orbitals ◽  
Complete Basis Set ◽  
Approximate Wave

<div> <div> <div> <p>We present an origin-invariant approach to compute the full optical rotation tensor (Buckingham/Dunn tensor) in the length dipole gauge without recourse to London atomic orbitals, called LG(OI). The LG(OI) approach is simpler and less computationally demanding than the more common LG-London and modified velocity gauge (MVG) approaches and it can be used with any approximate wave function or density functional method. We report an implementation at coupled cluster with single and double excitations level (CCSD), for which we present the first simulations of the origin-invariant Buckingham/Dunn tensor in the length gauge. With this method, we attempt to decouple the effects of electron correlation and basis set incompleteness on the choice of gauge for optical rotation calculations on simple test systems. The simulations show a smooth convergence of the LG(OI) and MVG results with the basis set size towards the complete basis set limit. However, these preliminary results indicate that CCSD may not be close to a complete description of the electron correlation effects on this property even for small molecules, and that basis set incompleteness may be a less important cause of discrepancy between choices of gauge than electron correlation incompleteness. </p> </div> </div> </div>

A DENSITY FUNCTIONAL THEORY INVESTIGATION ON THE TAUTOMERS AND CRYSTAL OF 2-DIAZO-4,6-DINITROPHENOL

2004 ◽  
Vol 03 (04) ◽  
pp. 599-607 ◽  
Author(s):  
XUE-HAI JU ◽  
HE-MING XIAO
Keyword(s):  
Density Functional ◽  
Density Functional Method ◽  
Lattice Energy ◽  
Functional Method ◽  
Basis Set ◽  
Functional Theory ◽  
Basis Set Superposition Error ◽  
Conduction Bands ◽  
Valence Bands ◽  
Good Agreement

Density functional method was applied to the study of the highly efficient primary explosive 2-diazo-4,6-dinitrophenol (DDNP) in both gaseous tautomers and its bulk state. Two stable tautomers were located. It was found that the structure (I) with open diazo, i.e. with linear CNN, is more stable than that with diazo ring tautomer (II) of DDNP. The structure I is in good agreement with the structure in the bulk. The lattice energy is -89.01 kJ/mol, and this value drops to -83.29 kJ/mol when a 50% correction of the basis set superposition error was adopted. The frontier bands are quite flat. The carbon atoms in DDNP make up the upper valence bands. While the lower conduction bands mainly consist of carbon and diazo N atoms. The bond populations of C–N bonds (both C–Nitro and C–Diazo) are much less than those of the other bonds and the detonation may be initiated through the breakdown of C–N bonds.

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