Thermochemistry, Bond Energies and Internal Rotor Potentials of Acetic Acid Hydrazide, Acetamide, <i>N</i>-Methyl Acetamide (NMA) and Radicals

• Main Authors: Sumit Charaya, Joseph W. Bozzelli
• Format: Article
• Language: English
• Published: MDPI AG 2021-03-01
• Series: Thermo
• Subjects: thermochemistry; enthalpy of formation; bond energy; acetohydrazide; acetamide and <i>N</i>-Methyl acetamide
• Online Access: https://www.mdpi.com/2673-7264/1/1/2

Structures, thermochemical properties, bond energies, and internal rotation potentials of acetic acid hydrazide (CH₃CONHNH₂), acetamide (CH₃CONH₂), and <i>N</i>-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 ΔH_f°(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=ONH_2, 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.