scholarly journals Thermochemistry, Bond Energies and Internal Rotor Potentials of Acetic Acid Hydrazide, Acetamide, N-Methyl Acetamide (NMA) and Radicals

Thermo ◽  
2021 ◽  
Vol 1 (1) ◽  
pp. 15-31
Author(s):  
Sumit Charaya ◽  
Joseph W. Bozzelli
Keyword(s):  
Acetic Acid ◽  
Acid Hydrazide ◽  
Molecular Structures ◽  
Enthalpies Of Formation ◽  
Bond Energies ◽  
Dft Methods ◽  
Dissociation Energies ◽  
Formation Enthalpies ◽  
Standard Enthalpies Of Formation ◽  
Internal Rotor

Structures, thermochemical properties, bond energies, and internal rotation potentials of acetic acid hydrazide (CH3CONHNH2), acetamide (CH3CONH2), and N-methyl acetamide (CH3CONHCH3), and their radicals corresponding to the loss of hydrogen atom, have been studied. Gas-phase standard enthalpies of formation and bond energies were calculated using the DFT methods B3LYP/6-31G(d,p), B3LYP/6-31G(2d,2p) and the composite CBS-QB3 methods employing a series of work reactions further to improve the accuracy of the ΔHf°(298 K). Molecular structures, vibration frequencies, and internal rotor potentials were calculated at the DFT level. The parent molecules’ standard formation enthalpies of CH3–C=ONHNH2, CH3–C=ONH2, and CH3–C=ONHCH3 were evaluated as −27.08, −57.40, and −56.48 kcal mol−1, respectively, from the CBS–QB3 calculations. Structures, internal rotor potentials, and C–H and N–H bond dissociation energies are reported. The DFT and the CBS-QB3 enthalpy values show close agreement, and this accord is attributed to the use of isodesmic work reactions for the analysis. The agreement also suggests this combination of the B3LYP/work reaction approach is acceptable for larger molecules. Internal rotor potentials for the amides are high, ranging from 16 to 22 kcal mol−1.

Bond Energies

2008 ◽  
Author(s):  
José A. Martinho Simões ◽  
Manuel Minas da Piedade
Keyword(s):  
Driving Forces ◽  
Theoretical Models ◽  
Enthalpies Of Formation ◽  
Chemical Bonds ◽  
Bond Energies ◽  
Bond Dissociation ◽  
Dissociation Energies ◽  
Or Groups ◽  
Quantum Chemistry Calculations ◽  
Standard Enthalpies Of Formation

Although standard enthalpies of formation provide information about the net stability of molecules and their transformations, they do not always indicate stability of individual bonds. This analysis normally involves parameters, loosely called “bond energies,” that reflect the amount of energy required to cleave chemical bonds. Bond energies are essential for understanding the nature of chemical bonds. They can be used to assess the results from quantum chemistry calculations (or from other, less sophisticated theoretical models) and thus support or oppose the descriptions of those bonds. Moreover, bond energy values also enable us to estimate the driving forces of chemical reactions by considering the strengths of all the bonds that are cleaved and formed. In fact, there are many reactions for which the standard enthalpies of formation of all reactants and products are not available (and cannot be easily estimated) but whose energetics can be predicted from the appropriate bond energies. In the previous chapters, we attempted to review all the important parameters in molecular energetics, but to avoid unnecessary distraction, we deliberately omitted bond energies from the discussion. The literature is plagued with a variety of concepts that fall into that designation but are not always synonymous. We can find names like bond strengths, bond enthalpies, bond energies, bond dissociation enthalpies, bond dissociation energies, bond disruption enthalpies, bond enthalpy terms, intrinsic bond energies, and symbols like D, D̄, 〈D〉, E, BDE, and so on. The meaning of these concepts it not always obvious and, unfortunately, some are occasionally misused. Now we look into each one of them. Consider a molecule AB, where A and B can be atoms or groups of atoms.

scholarly journals Enthalpies of formation of lanthanide oxyapatite phases

2001 ◽  
Vol 16 (10) ◽  
pp. 2780-2783 ◽  
Author(s):  
A. S. Risbud ◽  
K. B. Helean ◽  
M. C. Wilding ◽  
P. Lu ◽  
A. Navrotsky
Keyword(s):  
Structural Formula ◽  
Solution Calorimetry ◽  
Enthalpies Of Formation ◽  
Enthalpies Of Solution ◽  
Thermodynamic Cycles ◽  
Oxide Melt ◽  
Formation Enthalpies ◽  
High Temperature Oxide ◽  
Standard Enthalpies Of Formation ◽  
Temperature Oxide

A family of lanthanide silicates adopts an oxyapatitelike structure with structural formula Ln9.33 0.67(SiO4)6O2 (Ln = La, Sm, Nd, Gd,   = vacancy). The enthalpies of solution, ΔHS, for these materials and their corresponding binary oxides were determined by high-temperature oxide melt solution calorimetry using molten 2PbO B2O3 at 1078 K. These data were used to complete thermodynamic cycles to calculate enthalpies of formation from the oxides, ΔH0 f-oxides (kJ/mol): La9.33 0.67(SiO4)6O2 = 776.3 ± 17.9, Nd9.33 0.67(SiO4)6O2 = 760.4 ± 31.9, Sm9.33 0.67(SiO4)6O2 = 590.3 ± 18.6, and Gd9.33 0.67(SiO4)6O2 = 446.9 ± 21.9. Reference data were used to calculate the standard enthalpies of formation from the elements, ΔH0 f (kJ/mol): La9.33 0.67(SiO4)6O2 = 14611.0 ± 19.4, Nd9.33 0.67(SiO4)6O2 = 14661.5 ± 32.2, Sm9.33 0.67(SiO4)6O2 = -14561.7 ±; 20.8, and Gd9.33 0.67(SiO4)6O2 = -14402.7 ± 28.2. The formation enthalpies become more endothermic as the ionic radius of the lanthanide ion decreases.

Theoretical enthalpies of formation and structural characterisation of halogenated nitromethanes and isomeric halomethyl nitrites

2012 ◽  
Vol 66 (12) ◽  
Author(s):  
Agnie Kosmas ◽  
Aristeidis Ntivas ◽  
Stavroula Liaska ◽  
Demetrios Papayannis
Keyword(s):  
Density Functional ◽  
Strong Dependence ◽  
Enthalpies Of Formation ◽  
Induction Effect ◽  
Functional Theory ◽  
Structural Characterisation ◽  
Dissociation Energies ◽  
Species Formation ◽  
Stable Species ◽  
Formation Enthalpies

AbstractThe structural, energetic, and thermochemical properties of a number of halogenated nitromethanes, CHnX3−n NO2, and the isomeric nitrites, CHnX3−n ONO, are investigated, using theoretical ab initio and density functional theory (DFT) electronic structure methods. Analysis of the results and comparison with the maternal species, nitromethane, CH3NO2, and methyl nitrite, CH3ONO, reveal strong dependence of the molecular properties on the halogen induction effect. Opposite trends are obtained in the C—N and C—O bond dissociation energies (BDE) upon halogenation and higher stabilities are calculated for the trans-nitrite isomers, in contrast with the plain alkyl families where the nitroalkanes are the most stable species. Formation enthalpies, ΔH fℴ, at 298 K are calculated for all halogenated isomers.

PREDICTION OF THE ENTHALPY OF FORMATION OF HYDROCARBONS USING SPARC

2004 ◽  
Vol 03 (03) ◽  
pp. 451-469 ◽  
Author(s):  
TAD S. WHITESIDE ◽  
LIONEL A. CARREIRA
Keyword(s):  
Perturbation Theory ◽  
Aromatic Hydrocarbons ◽  
Chemical Structure ◽  
Molecular Structures ◽  
Structure Theory ◽  
Enthalpies Of Formation ◽  
Computational Algorithms ◽  
Intrinsic Properties ◽  
Standard Enthalpies Of Formation ◽  
The Enthalpy Of Formation

Standard enthalpies of formation (ΔHf) were calculated with models developed using the computer program SPARC. SPARC uses computational algorithms based on chemical structure theory to calculate the ΔHf. Molecular structures are broken into simple functional units (reactophores) with intrinsic properties. Each reactophore is analyzed and the effects of appended molecular structures are quantified through perturbation theory. The ΔHf models have been developed using all known data for saturated and unsaturated hydrocarbons. The structures of these compounds vary from chains to conjugated rings to poly-benzoic aromatic hydrocarbons. The SPARC calculated RMS deviation of these 587 compounds is 4.50 kJ mol-1.

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