| Summary: | Structures, thermochemical properties, bond energies, and internal rotation potentials of acetic acid hydrazide (CH<sub>3</sub>CONHNH<sub>2</sub>), acetamide (CH<sub>3</sub>CONH<sub>2</sub>), and <i>N</i>-methyl acetamide (CH<sub>3</sub>CONHCH<sub>3</sub>), 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 ΔH<sub>f</sub>°(298 K). Molecular structures, vibration frequencies, and internal rotor potentials were calculated at the DFT level. The parent molecules’ standard formation enthalpies of CH<sub>3</sub>–C=ONHNH<sub>2</sub>, CH<sub>3</sub>–C=ONH<sub>2,</sub> and CH<sub>3</sub>–C=ONHCH<sub>3</sub> were evaluated as −27.08, −57.40, and −56.48 kcal mol<sup>−1</sup>, 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<sup>−1</sup>.
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