Ab initio Studies of Hydrazines: Equilibrium Structures of 1,1-Dimethylhydrazine and Transition Structures Connecting Them

1987 ◽  
Vol 40 (11) ◽  
pp. 1783 ◽  
Author(s):  
NV Riggs ◽  
L Radom
Keyword(s):  
Internal Rotation ◽  
Vibrational Energy ◽  
Zero Point ◽  
Basis Set ◽  
Basis Sets ◽  
Primary Amines ◽  
Rotational Angle ◽  
Small Rise ◽  
Equilibrium Structures ◽  
Anti Form

Optimization of the geometries of various stationary structures of 1,1-dimethylhydrazine has been carried out with the 3-21G and 3-21G(N*) basis sets, and the energies of each of the latter optimized structures have been evaluated with the 6.31G* basis set. The gauche form with a (mean) internal rotational angle near 80� (hydrazine, approx. 90�) is the lowest-energy form. After zero-point vibrational -energy corrections, the anti form lies in a shallow well 14kJ mol-1 higher on the potential-energy surface for internal rotation, and the transition structure connecting them lies approx. 1 kJ mol-1 higher still. The anti form is thus a true equilibrium species, unlike the case for hydrazine, but constitutes less than 0.5% of the molecules present at room temperature. It is estimated to have a half-life of less than 10 ps , so its observation by present physical methods may prove to be difficult. The barrier to internal rotation via the syn form (41kJ mol-1) coincides with that for hydrazine. gem-Dimethyl substitution in hydrazine leads to a small rise (1-2 kJ mol-1) in the barrier to inversion at the unsubstituted nitrogen atom, but to an unexpectedly high (by 8-9 kJ mol-1) calculated barrier to inversion at the substituted centre, whether the result be referred to the barrier in hydrazine or to that in dimethylamine. Calculated NH stretching frequencies for the gauche form show a spacing much larger than that for 'simple' primary amines, as is found experimentally.

An ab initio Study of the Equilibrium Structures of Prop-2-ynamine (Propargylamine) and the Transition Structures Connecting Them

1987 ◽  
Vol 40 (3) ◽  
pp. 435 ◽  
Author(s):  
NV Riggs
Keyword(s):  
Ab Initio ◽  
Internal Rotation ◽  
Vibrational Energy ◽  
Vibrational Analysis ◽  
Zero Point ◽  
Basis Set ◽  
Basis Sets ◽  
Experimental Result ◽  
Transition Structure ◽  
Equilibrium Structures

Optimization with the 3-21G and 3-21G(N*) basis sets finds, in agreement with previous ab initio studies and the experimental result, the anti conformation of prop-2-ynamine to be of lowest energy and, after zero-point vibrational -energy ( Ezpv ) corrections, the gauche form to lie 11 kJ mol-l higher; by vibrational analysis, both are confirmed as equilibrium structures. The synform was not able to be optimized with the 3.21G basis set but, with the 3-21G(N*) basis set, is found to lie 8.6 kJ mol-1 (after Ezpv corrections) above the gauche form, and is shown by vibrational analysis to be a transition structure connecting enantiomeric gauche forms by internal rotation about the N-C bond. The transition structure connecting gauche and anti forms by internal rotation lies 6.3 kJ mol-1 (after Ezpv corrections) above the gauche form, and the transition structure for inversion at the nitrogen atom lies 31.1 kJ mol- l (after Ezpvcorrections) above the anti form.

Determination of the Absolute Configuration of 1,5-Diaza-cis-decalin by Comparison of Measured and Calculated CD-Spectra

1998 ◽  
Vol 53 (10-11) ◽  
pp. 896-902 ◽  
Author(s):  
Jörg Fleischhauer ◽  
Gerhard Raabe ◽  
A. G. Santos ◽  
Jan Schiffer ◽  
Axel Wollmer
Keyword(s):  
Absolute Configuration ◽  
Vibrational Energy ◽  
Zero Point ◽  
Equilibrium Mixture ◽  
Cotton Effect ◽  
Basis Set ◽  
Basis Sets ◽  
Cd Spectra ◽  
The Absolute

Abstract The absolute configurations of both 1,5-diaza-c/s-decalin enantiomers were determined by com-parison of measured and calculated CD spectra.CD spectra for both enantiomers were recorded. Theoretical CD spectra for one of the isomers were calculated by means of the semiempirical CNDO/2S method. Eight local minima on the energy hypersurface of the title compound were used to describe the conformer equilibrium mixture. The geometries of these conformers were calculated employing one-determinant ab initio calculations using the split valence 6-31G* basis set. Boltzmann factors were then obtained using relative energies calculated with three different basis sets and including correlation(MP2)-and zero point vibrational energy.Comparing the sign of the observed and calculated longest wavelength Cotton effect, we assign an absolute configuration to the compound. This assignment was verified by means of X-ray structure determination of one of the enantiomers’ α-methoxy-α-trifluoromethylphenyl aceticacid (MTPA, Mosher’s reagent) derivative.

An ab initio Investigation of the Equilibrium Structures of Hydrazine and of the Transition Structures Connecting Them

1986 ◽  
Vol 39 (12) ◽  
pp. 1917 ◽  
Author(s):  
NV Riggs ◽  
L Radom
Keyword(s):  
Potential Energy ◽  
Ab Initio ◽  
Internal Rotation ◽  
Energy Surface ◽  
Vibrational Energy ◽  
Vibrational Analysis ◽  
Basis Sets ◽  
Transition Structure ◽  
Transition Structures ◽  
Anti Form

An ab initio investigation of the various equilibrium and transition structures of hydrazine has been carried out with full geometry optimization and use of the 3-21G, 3-21G(N*), and 6-31G* basis sets. Best estimates of relative energies (as quoted below) were obtained by evaluation of total electronic energies at the MP3/6-31G**//6-31G* level. By vibrational analysis, it was confirmed that the gauche form is an equilibrium species and that the syn form, which lies 39.8 kJ mol-1 above the gauche form, is a transition structure connecting enantiomeric gauche forms by internal rotation. The anti form, characterized by vibrational analysis as an equilibrium species on the STO-3G, 3-21G, and 6-31G* potential-energy surfaces, lies in a shallow minimum 7.7 kJ mol-1 above the gauche form. A transition structure connecting gauche and anti forms by internal rotation lies, however, only 0.4 kJ mol-1 higher on the electronic-energy surface and, after zero-point vibrational -energy corrections, 0.3 kJ mol-1 below the anti form which is, therefore, the true transition structure. The transition structure for inversion at one nitrogen atom of the gauche form is shown to be a CS structure lying 26.2 kJ mol-1 above the gauche form itself. Various other structures, including those of D2h and D2d symmetry, are discussed briefly and shown by vibrational analysis to be neither equilibrium species nor true transition structures on the 3-21G potential-energy surface. Finally, the complete potential function for internal rotation has been evaluated at levels up to MP3/6-31G**//HF/6- 31G*, and the coefficients of the corresponding four-term Fourier cosine series are presented and briefly discussed.

Ab initio Studies on Hydrazines: 1H-Pyrrol-1-amine (N-Aminopyrrole)

1988 ◽  
Vol 41 (3) ◽  
pp. 397 ◽  
Author(s):  
NV Riggs ◽  
L Radom
Keyword(s):  
Saddle Point ◽  
Ab Initio ◽  
Pyrrole Ring ◽  
Vibrational Energy ◽  
Zero Point ◽  
Equilibrium Structure ◽  
Basis Sets ◽  
Primary Amines ◽  
Transition Structure ◽  
Zero Point Vibrational Energy

The geometries of four stationary structures of 1H-pyrrol-1-amine have been optimized with the 3-21G and 3-21G(N*) basis sets. The lowest- energy and only equilibrium structure is the 'perpendicular' CS form (4) in which a pyramidal NH2 group is bisected by the plane of the pyrrole ring. The transition structure for inversion at the NH2 group is the perpendicular C2V form (2). After zero-point vibrational -energy corrections, it lies 24.5 kJ mol-1 [3-21G(N*)] above (4). The transition structure for rotation about the N-NH2 bond is the 'parallel' CS form (3) in which a plane of symmetry bisects both the pyrrole ring and the attached pyramidal NH2 group; it lies 26.5 kJ mol-1 above (4). The planar C2V structure (1) is a second-order saddle point lying 69.4 kJ mol-1 above (4). The spacing of NH-stretching frequencies calculated for the equilibrium structure (4) of 1H-pyrrol-1-amine is in the range for normal primary amines, unlike that for 1,1-dimethylhydrazine.

scholarly journals Synthesis, Spectroscopic Investigation and Computational Studies of 2-Formyl-4-(Phenyldiazenyl)Phenyl Methyl Carbonate and 4-((4-Chlorophenyl)Diazenyl)-2-Formylphenyl Methyl Carbonate

2016 ◽  
Vol 66 ◽  
pp. 38-70 ◽  
Author(s):  
A. Arokiasamy ◽  
G. Manikandan ◽  
V. Thanikachalam ◽  
K. Gokula Krishnan
Keyword(s):  
Total Energy ◽  
Density Functional ◽  
Vibrational Energy ◽  
Zero Point ◽  
Basis Set ◽  
Stable Configuration ◽  
Vibrational Assignments ◽  
Computational Optimization ◽  
Methyl Carbonate ◽  
Surface Scan

Two new compounds namely 2-formyl-4-(phenyldiazenyl)phenyl methyl carbonate (FPMC) and 4-((4-chlorophenyl) diazenyl)-2-formylphenyl methyl carbonate (CFPMC) have been synthesized and have characterized using FT-IR, FT-Raman,1H and13C NMR techniques. Computational optimization studies have been carried out using Hatree–Fock (HF) and Density Functional Theory (DFT–B3LYP) methods with 6–31+G(d, p) basis set ofGaussian 09Wsoftware. The stable configuration of the title compounds were achieved theoretically by potential energy surface scan analysis. The complete vibrational assignments were performed on the basis of total energy distribution (TED) and natural bonding orbital (NBO) have been studied. Various parameters such as EHOMO, ELUMO,total energy, dipole moment, polarizability, first order hyperpolarizability, zero–point vibrational energy as well as thermal properties were analyzed and reported for the title compounds.

Ab initio Studies on Hydrazines: 4H-1,2,4-Triazol-4-amine

1989 ◽  
Vol 42 (10) ◽  
pp. 1623 ◽  
Author(s):  
NV Riggs
Keyword(s):  
Saddle Point ◽  
Relative Intensity ◽  
Vibrational Energy ◽  
Zero Point ◽  
Equilibrium Structure ◽  
Vibrational Frequencies ◽  
Basis Sets ◽  
Transition Structure ◽  
Intensity Pattern ◽  
Zero Point Vibrational Energy

The geometries of four stationary structures of 4H-1,2,4-triazol-4-amine have been optimized with the 3-21g and 3-21g(N*) basis sets. The lowest-energy and only equilibrium structure predicted by these calculations is the 'perpendicular' CS form (7). All its calculated vibrational frequencies are real and, after zero-point vibrational-energy corrections, it lies 26.9 kJ mol-1 below the 'parallel' C, structure (6), here characterized as the transition structure for internal rotation about the N-NH2 bond (cf. 26.5 kJ mol-1 for the corresponding structures of 1H-pyrrol-1-amine, but only 8.7 kJ mol-1 for the corresponding structures of 2H-1,2,3-triazol-2-amine). The transition structure for inversion at the NH2 centre is, as for 1H-pyrrol-1-amine and 2H-1,2,3-triazol-2-amine, the perpendicular C2v � structure (5), the barrier being 21.4 kJ mol-1 (cf. 24-26 kJ mol-1 for the two reference azolamines ). The planar C2v structure (4) is a second-order saddle point lying 66.6 kJ mol-1 above the equilibrium structure (cf. 69.4 kJ mol-1 for 1H-pyrrol-1-amine, but only 41 .7 kJ mol-1 for 2H-1,2,3-triazol-2-amine). The calculated NH-stretching vibrational frequencies for 4H-1,2,4-triazol-4-amine are c. 20 cm-1 higher than those of 1H-pyrrol-1-amine and their splitting is c. 8 cm-1 greater but they show a very similar relative-intensity pattern, quite unlike that calculated for 2H-1,2,3-triazol-2-amine. ′

Abinitio interpretation of conformer stabilization through bonding in the acetyl derivatives of two representative heterocyclic methine bases

1995 ◽  
Vol 73 (8) ◽  
pp. 1287-1293 ◽  
Author(s):  
Kathleen M. Gough ◽  
Janice Millington
Keyword(s):  
Internal Rotation ◽  
Closed Shell ◽  
Theoretical Explanation ◽  
Atoms In Molecules ◽  
Basis Set ◽  
Basis Sets ◽  
Side Chain ◽  
Derivatives Of ◽  
Favorable Structure ◽  
Oxygen Interaction

Abinitio calculations (STO-3G and 3-21G* basis sets) have been performed on 2 and 3 to determine the most favorable structure and to provide an estimate of the barrier to internal rotation of the acyl group. The Z configuration is preferred in 2, the E configuration in 3, with calculated barriers to internal rotation of 79.9 and 68.7 kJ/mol, respectively, at the 3-21G* level. The wave functions from the 3-21G* calculations are analyzed with the theory of atoms in molecules. The identification of bond critical points characteristic of a closed shell interaction establishes the existence of a weak bond between [Formula: see text] in 2 and between [Formula: see text] in 3, for the preferred configurations. The energy required to break this bond as well as the loss of extended conjugation throughout the hetero ring and its side chain are responsible for the asymmetry in the barrier. These findings provide a theoretical explanation for experimental observations on this class of molecules in which one conformer is preferred to any other and only one crystal structure is identified. Keywords: nonbonded sulfur–oxygen interaction, closed shell interaction, hydrogen bonding, 3-21G* basis set, theory of atoms in molecules.

Interatomic Potential and Thermodynamic Property of Diatomic Uranium

2012 ◽  
Vol 550-553 ◽  
pp. 2810-2813 ◽  
Author(s):  
Xiu Lin Zeng ◽  
Xue Hai Ju ◽  
Si Yu Xu
Keyword(s):  
Density Functional ◽  
Vibrational Energy ◽  
Interatomic Potential ◽  
Zero Point ◽  
Dft Method ◽  
Basis Set ◽  
Functional Theory ◽  
Lennard Jones ◽  
Anharmonicity Constant ◽  
The Relationship

Potential energy scan for U2 was performed by density functional theory (DFT) method at the B3LYP level in combination with the (ECP80MWB_AVQZ + 2f) basis set. The dissociation energy of U2, after being corrected for the zero-point vibrational energy, is 2.482 eV, which is in good agreement with the experiment. The calculated energy was fit to the typical potential functions of Morse, Lennard-Jones (L-J) and Rydberg. Both the Morse and Rydberg functions are good representatives of the potentials, but the Lennard-Jones function is not. The anharmonicity constant is very small. The anharmonic frequency is 113.99 cm–1. Thermodynamic properties of entropy and heat capacity at 298.2 K – 1500 K were calculated by using DFT-B3LYP computational results and Morse parameters, respectively. The relationship between entropy and temperature was established.

An ab initio study of the structures, barriers for internal rotation, vibrational frequencies, and thermodynamic functions of the hydrochlorofluorocarbon CH3CF2Cl and the corresponding radical CH2CF2Cl

1994 ◽  
Vol 72 (3) ◽  
pp. 561-567 ◽  
Author(s):  
S.J. Paddison ◽  
Yonghua Chen ◽  
E. Tschukow-Roux
Keyword(s):  
Ab Initio ◽  
Internal Rotation ◽  
Vibrational Energy ◽  
Zero Point ◽  
Heat Of Formation ◽  
Vibrational Frequencies ◽  
Radical Center ◽  
Molecular Orbital Calculations ◽  
Parent Molecule ◽  
Moller Plesset

Ab initio molecular orbital calculations were performed using the GAUSSIAN 90 system of programs at the HF/6-31G* level of theory, on the hydrochlorofluorocarbon (HCFC) 1-chloro-1,1-difluoroethane and the 1-chloro-1,1-difluoroethyl radical. Equilibrium geometries, barriers for internal rotation, and harmonic vibrational frequencies were thus calculated. A single conformational minimum in the potential energy surface was located for both the radical and the parent molecule. The radical center in CH2CF2Cl was found to be nonplanar. Transition structures for internal rotation about the C—C bond were located for both the molecule and the radical using analytical methods. The rotation barriers, evaluated at the fourth-order Møller–Plesset perturbation theory ((U)MP4/6-311G**/6-31G*). were calculated after inclusion of zero-point vibrational energy differences to be 1.11 and 4.12 kcal/mol for the radical and the parent molecule, respectively. Computed thermodynamic properties including heat capacity, entropy, enthalpy, and free energy functions are reported as a function of temperature. Using an experimentally measured heat of formation of CH3CF2Cl at 298 K, the heat of formation of CH2CF2Cl was calculated to be −74.3 ± 1.7 kcal/mol. Tabulations of ΔH0f,T, ΔG0f,T, and log10Kf,T over the temperature range of 0–1500 K are also reported for both species.

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