Thermochemistry and bond energies of acetohydrazide, amides and cyclic alkyl ethers
Department of Chemistry and Environmental Science
Master of Science
Bozzelli, Joseph W.
Gund, Tamara M.
Acetic acid hydrazide
Structure, 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 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 to further improve accuracy of the ΔHf°(298K). Molecular structures, vibration frequencies and internal rotor potentials were calculated at DFT level. The enthalpies of the parent molecules CH3-C=ONHNH2, CH3-C=ONH2 and CH3-C=ONHCH3 are evaluated as -28.6, -58.1 and -56.5 kcalmol-1 respectively at B3LYP/6-31G(D,P), B3LYP/6-31G(2d,2p) and CBS-QB3 levels. Bond dissociation energies for H--CH2C=ONHNH2, CH3-C=ON(--H)NH2, CH3- C=ONHNH--H, H--CH2C=ONH2, CH3-C=ONH--H, H--CH2-C=ONHCH3, CH3-C=ON(- -H)CH3 and CH3-C=ONHCH2—H are 99.9, 78.2, 81.9, 100.1, 111.5, 99.9, 104.2 and 93.7 kcal mol-1 respectively. The computed DFT and the Complete Basis Set enthalpy values are in close agreement with each other; and this accord is attributed to use of isodesmic work reactions for the analysis. The agreement also suggests this combination of B3LYP / work reaction approach is acceptable for larger molecules.
Cyclic ethers are a major initial product from the reactions or hydrocarbon radicals with triplet dioxygen (3O2) in low to moderate temperature oxidation and combustion reaction systems and atmospheric chemistry of small hydrocarbons. Thermochemical properties, ΔH°f(298), S°298 and Cp° (T) (10K<T<5000 K) of eight target cyclic alkyl ethers were calculated using density functional methods. Density functional theory (DFT) calculations, based on the B3LYP method, were performed to determine thermochemistry and C—H Bond Dissociation Energies (BDE’s) governing the thermochemical stabilization of the radicals of cyclic alkyl ethers. Enthalpies of formation of different cyclic alkyl ether (oxiranes, oxetanes and oxolanes) radicals are calculated using isodesmic reactions at the B3LYP/6-31G(d,p) and B3LYP/6-31G(2d,2p) level of theory. Knowledge of these properties allows combustion and atmospheric scientists to estimate reaction paths and kinetics for these intermediates.
njit-etd2011-071 (106 pages ~ 1,616 KB pdf)
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Created August 18, 2011