scholarly journals Charge distributions and chemical effects. XXIX. On the vibrational energies of chair and boat cyclohexane

1982 ◽  
Vol 60 (11) ◽  
pp. 1347-1351 ◽  
Author(s):  
J. P. Huvenne ◽  
G. Vergoten ◽  
G. Fleury ◽  
S. Odiot ◽  
S. Fliszár
Keyword(s):  
Force Field ◽  
Conformational Changes ◽  
Vibrational Energy ◽  
Zero Point ◽  
Local Symmetry ◽  
Cyclohexane Ring ◽  
Force Field Calculations ◽  
Similar Nature ◽  
Chemical Effects ◽  
Vibrational Energies

Local symmetry force field calculations are presented for the chair and boat forms of cyclohexane and the assignments of frequencies are given. The calculated zero-point and thermal vibrational energies indicate a near invariance of total vibrational energy with respect to chair–boat conformational changes of the cyclohexane ring, thus confirming results of similar nature derived from earlier theoretical thermochemical analyses.

Charge distributions and chemical effects. XXIV. On the role of vibrational energies in determining molecular stabilities

1981 ◽  
Vol 59 (9) ◽  
pp. 1381-1387 ◽  
Author(s):  
Sándor Fliszár ◽  
J.-L. Cantara
Keyword(s):  
Conformational Changes ◽  
Vibrational Energy ◽  
Heat Content ◽  
Zero Point ◽  
Enthalpies Of Formation ◽  
Chemical Binding ◽  
Nuclear Magnetic Resonance Spectra ◽  
Molecular Stability ◽  
Coulomb Type ◽  
Vibrational Energies

A simple equation has been derived for calculating accurate ZPE + HT − H0 (zero-point and heat content) energies of saturated hydrocarbons from their enthalpies of formation and carbon-13 nuclear magnetic resonance spectra. Applications to conformational analysis indicate a near invariance of vibrational energies with respect to chair–boat conformational changes of the cyclohexane ring, the loss in molecular stability arising then from a weakening of the chemical binding due to a reorganization of the electronic charges. The origin of the destabilizing effect of butane gauche interactions is found, in the cyclohexane series, in a weakening of the chemical binding (∼1.85 kcal/mol) which is partially compensated by a lowering (∼0.85 kcal/mol) vibrational energy, thus offering an explanation for the loss in molecular stability of ∼1.00 kcal/mol for one gauche interaction without invoking Coulomb-type repulsions between non-bonded atoms. Calculated enthalpies of formation are presentd for a number of cycloalkanes.

Charge distributions and chemical effects. XXXI. Molecular energies of ethylenic compounds

1983 ◽  
Vol 61 (1) ◽  
pp. 197-205 ◽  
Author(s):  
M.-T. Béraldin ◽  
S. Fliszâr
Keyword(s):  
Zero Point ◽  
Enthalpies Of Formation ◽  
Average Deviation ◽  
Bond Forming ◽  
Chemical Effects ◽  
Nuclear Magnetic Resonance Spectra ◽  
Energy Formula ◽  
Standard Enthalpies Of Formation ◽  
Vibrational Energies ◽  
Proper Consideration

The energy formula describing bond contributions in terms of the charges carried by the bond-forming atoms is applied to ethylenic compounds. It is shown in what manner σ and π electrons can be treated within the framework of the bond energy theory giving the atomization energy of the vibrationless molecule at 0 K. Proper consideration of zero-point and thermal vibrational energies leads to standard enthalpies of formation. These calculations, which are carried out on the basis of, 13C nuclear magnetic resonance spectra, agree with their experimental counterparts, within experimental uncertainties (~0.3 kcal mol−1 average deviation).

scholarly journals Thermodynamics and Intermolecular Interactions of Nicotinamide in Neat and Binary Solutions: Experimental Measurements and COSMO-RS Concentration Dependent Reactions Investigations

2021 ◽  
Vol 22 (14) ◽  
pp. 7365
Author(s):  
Piotr Cysewski ◽  
Maciej Przybyłek ◽  
Anna Kowalska ◽  
Natalia Tymorek
Keyword(s):  
Intermolecular Interactions ◽  
Vibrational Energy ◽  
Perfect Match ◽  
Zero Point ◽  
Heat Capacity Change ◽  
Free Energies ◽  
Temperature Dependent ◽  
Scanning Calorimetry ◽  
Capacity Change ◽  
Self Association

In this study, the temperature-dependent solubility of nicotinamide (niacin) was measured in six neat solvents and five aqueous-organic binary mixtures (methanol, 1,4-dioxane, acetonitrile, DMSO and DMF). It was discovered that the selected set of organic solvents offer all sorts of solvent effects, including co-solvent, synergistic, and anti-solvent features, enabling flexible tuning of niacin solubility. In addition, differential scanning calorimetry was used to characterize the fusion thermodynamics of nicotinamide. In particular, the heat capacity change upon melting was measured. The experimental data were interpreted by means of COSMO-RS-DARE (conductor-like screening model for realistic solvation–dimerization, aggregation, and reaction extension) for concentration dependent reactions. The solute–solute and solute–solvent intermolecular interactions were found to be significant in all of the studied systems, which was proven by the computed mutual affinity of the components at the saturated conditions. The values of the Gibbs free energies of pair formation were derived at an advanced level of theory (MP2), including corrections for electron correlation and zero point vibrational energy (ZPE). In all of the studied systems the self-association of nicotinamide was found to be a predominant intermolecular complex, irrespective of the temperature and composition of the binary system. The application of the COSMO-RS-DARE approach led to a perfect match between the computed and measured solubility data, by optimizing the parameter of intermolecular interactions.

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