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

Department of Chemistry and Environmental Science, New Jersey Institute of Technology, Newark, NJ 07102, USA
*
Author to whom correspondence should be addressed.
Academic Editor: Johan Jacquemin
Received: 24 November 2020 / Revised: 18 February 2021 / Accepted: 19 February 2021 / Published: 2 March 2021

Abstract

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.
Keywords: thermochemistry; enthalpy of formation; bond energy; acetohydrazide; acetamide and N-Methyl acetamide thermochemistry; enthalpy of formation; bond energy; acetohydrazide; acetamide and N-Methyl acetamide

1. Introduction

Thermochemical and spectroscopic investigation of N-methyl Acetamide (NMA) and other substituted amides are considered as model compounds for the peptide bonds in proteins; understanding their thermochemistry can provide information about the secondary structure of proteins in the gas phase as well as inferences in solution and helpful information toward understanding kinetics. There are no studies that we are aware of that have targeted these molecules’ thermochemical properties and bond energies.
There are several reasons for interest in the structure and chemistry of these amide systems. These include: (i) clear understanding of the NMA structure is considered as the basis for understanding the geometric constraints imposed by the peptide linkages that determine, at least partly, the protein structure; (ii) detailed understanding of NMA spectroscopic features is assumed as the fundamental basis for spectroscopic methods to monitor protein structure and dynamics [1]. Both of these properties are of interest for future applications, only if both structures and spectroscopic properties of NMA are observed in the natural environment of the biological system(s).
There are many infrared (I.R.), and Raman experiments that have focused on the spectral region spanned by the three amide bands of NMA, particularly in the easily detectable I.R. amide I regime that overlaps with the C.O. stretch. In water (aq), the C.O. stretch responds to water molecules’ presence by forming hydrogen bonds, and the resulting frequency shift can be used to assess the dynamics of protein–solvent interactions [2,3,4,5,6,7,8,9]. Similarly, the amide II and amide III bands, which overlap with the N.H. in-plane wagging motion, can be used to describe the interaction between C.O. and H.N., which are part of a protein backbone. The amide hydrogen can also form a hydrogen bond with the solvent (H2O∙HN), and the corresponding frequency shift provides further information on protein behavior in an aqueous solution [10].
The structural stability of acetohydrazide CH3–CO–NH–NH2 was investigated by DFT-B3LYP and ab initio MP2 calculations with a 6-311+G ** basis set. The C–N rotational barrier in the molecule was calculated to be 26 kcal mol−1, which suggested the planar sp2 nature of the nitrogen atom of the central N.H. moiety with the two-fold barrier. The N atom of the terminal NH2 group was predicted to prefer the pyramidal sp3 structure with an inversion barrier of 7–8 kcal mol−1. The molecule was predicted to have a trans–syn (N–H bond is trans with respect to C=O bond and the NH2 moiety is syn to C–N bond) conformation as the lowest energy structure. The vibrational frequencies were computed at the B3LYP/6-311+G ** level of theory and normal coordinate calculations were carried out for the trans–syn acetohydrazide. Complete vibrational assignments were made based on normal coordinate analyses and experimental infrared and Raman data [11].
The study of amide C–N rotation barriers is important because amide C–N bonds make up protein backbones. The preferred amide conformations play an important role in enzyme structure and the barrier to the rotation affects the rigidity of the structure. The rigidity of an enzyme’s structure can affect its selectivity in binding substrates. Ab initio calculations by Jasien et al. [12] have been used to determine the gas-phase rotational barrier about the C-N bond in acetamide. Their results indicate that the inclusion of polarization functions in the basis sets leads to a substantial decrease (ca. 5 kcal mol−1) in the calculated barrier height at the H.F.–SCF level. Electron correlation effects decrease the barrier by less than 1 kcal mol−1, while the addition of zero-point energy corrections changed the barrier height only slightly. Based upon the current (DZ + d/SCF) calculations, the 0 K rotational barrier for acetamide is predicted to be 12.5 kcal mol−1. An investigation of the photolysis of acetamide was performed using light in the 250 Å regions of the spectrum, where the goal was to break down the molecule into CH3 and CONH2 radicals. The authors reported this was probably accompanied by a second process yielding CH3CN and H2O. Methyl radicals were observed to react with the parent acetamide and with the CONH2 radical to give methane as a product and to recombine yielding ethane. The CONH2 radicals were reported to decompose both spontaneously and thermally to give C.O. and NH2 radicals. The subsequent reaction of the NH2 radicals with Acetamide gives ammonia. In a separate experiment with acetone as a photo methyl radical source, the activation energy for the abstraction of hydrogen by methyl radical was found to be 9.2 kcal mol−1 [13].
The importance of reliable and accessible thermochemical data (enthalpies of formation, entropies, and heat capacities) is universally accepted among scientists and engineers. This work provides thermochemical data for acetic acid hydrazide, acetamide, and N-methyl acetamide and their radicals corresponding to the loss of hydrogen atoms through the use of computational chemistry.

2. Computational Methods

Density functional theory and composite calculations via series of isodesmic reactions: the structure and thermochemical parameters of CH3CONHNH2, CH3CONH2, and CH3CONHCH3 are based on the density functional and composite ab initio levels using Gaussian 98 [14] and Gaussian 09 [15]. Computation levels include B3LYP/6-31G(d,p), B3LYP/6-31G(2d,2p). These methods combine the three-parameter Becke exchange functional B3 [16], with the Lee–Yang–Parr correlation functional, LYP, [17], and are used here with the 6-31G(d,p) basis set. B3LYP/6-31G(d,p) is chosen because it is computational, economical, and, thus, possibly applicable to larger molecules [18]. Energies are further refined using the procedures of the complete basis method developed by Petersson and co-workers, CBS-QB3 [19]. The CBS-QB3 method is utilized for improved energies and serves to check the DFT calculations. CBS models, a series of calculations made on a defined geometry, and a complete basis set model chemistry including corrections for basis set truncation errors. These methods show accuracy in structure and energy that requires convergence in basis set size and the degree of correlation [18].
Standard enthalpies of formation for stable species are calculated using the total energies at B3LYP/6-31G(d,p), B3LYP/6-31G(2d,2p), and CBS-QB3 levels with work reactions that are isodesmic in most cases. Isodesmic reactions conserve the number and type of bonds on both sides of an equation. The use of a work reaction with similar bonding on both sides of an equation results in a cancellation of calculation error and improves the accuracy for energy analysis [20]. The reported enthalpy values can be compared with the known enthalpies of several molecules in the system to serve as a calibration on the thermochemistry.
Contributions to S°298 and Cp°(T) of each species are calculated using the “SMCPS” (Statistical Mechanics for Heat Capacity and Entropy Cp and S) program, which incorporates the frequencies, moments of inertia, mass, symmetry, number of optical isomers, from the Gaussian calculation. It also incorporates frequency corrections. Contributions from hindered internal rotors to S°298 and Cp(T) are determined using the “VIBIR” program. The hindered rotor corrections to the S°298 and Cp(T) are obtained by adding the S and Cp values, respectively, obtained by employing the VIBIR program to those obtained from SMCPS.

3. Results and Discussion

Optimized, lowest energy structures of the parent molecules—acetohydrazide, acetamide, and N-methyl acetamide are shown in Figure 1.
The torsional potentials of CH3–C=ONHNH2 and CH3–C=ONHCH3 (vide infra) show that corresponding anti- and syn-isomers respective to H8N7---C5O6 dihedral angles (see Figure 3). The anti-acetohydrazide has a near −4.86 kcal mol−1 lower energy than for the syn configuration, with a 20.7 kcal mol−1 barrier to the internal rotation converting the two-isomer configuration.
In contrast, the syn-N-methyl acetamide has a near −2.50 kcal mol−1 lower energy than for the anti-configuration, with a 19.3 kcal mol−1 barrier. The internal rotation energies for these synanti isomerizations are high, typically greater than 13 kcal mol−1 (see below). This isomerization does not occur at standard temperature, and the isomers should be considered as different molecules in their thermochemistry and probably in their reactions.
The optimized geometries at the B3LYP/6-31G (d,p) density functional calculation level for CH3–C=ONHNH2, CH3–C=ONH2, and CH3–C=ONHCH3 are presented in the Supplementary Materials [SM]. The Geometric Parameters (See Section SM0, Tables S1–S3 of the SM) are listed.

3.1. Enthalpies of Formation of the Parent Molecules

Enthalpies of formation (ΔHf°298) of the parent molecules have been determined using corresponding ΔHrxn (298) from the enthalpy of reaction in the isodesmic work reactions and calculated enthalpies of each species. The standard enthalpies of formation of the reference molecules at 298.15 K and the calculated ΔHrxn°298 are used to calculate the ΔfHrxn°298 of the target molecule; the enthalpies are summarized in Table 1.
ΔHrxn°298 = Σ Hf products − Σ Hf reactants
The work reactions and the enthalpies obtained from three isodesmic reactions for the parent molecules are listed in Table 2. Comparing the values of the enthalpies of the parent molecules calculated by two DFT and the CBS-QB3 methods shows that the values obtained by the DFT methods method are in close agreement with those obtained by CBS-QB3 calculations. We recommend the values obtained by the CBS-QB3 because it is a composite method and is known to have higher accuracy. The agreement of the DFT values suggests that the use of B3LYP calculations with the 6-31G(d,p) and 6-31G(2d,2p) basis sets coupled with work reactions results in the cancelation of error and provides reasonable results for these amide systems.
The recommended enthalpies of formation for the CH3–C=ONHNH2, CH3–C=ONH2, and CH3–C=ONHCH3 molecules obtained in this study are: −27.08 kcal mol−1, −57.40 kcal mol−1, and −56.48 kcal mol−1 by the CBS-QB3 calculation method.
Moments of Inertia (See Section SM1, Table S4 of the SM), vibrational frequencies (Table S5 of the SM), and Mulliken Atomic Charges(Section SM2, Tables S6–S8 of the SM) of CH3–C=ONHNH2, CH3–C=ONH2, and CH3–C=ONHCH3 and their radicals are calculated and presented.

3.2. Radicals Corresponding to the Loss of a Hydrogen Atom

Optimized, lowest energy structures of the radicals derived from the target parent molecules are illustrated in Figure 2.
The radicals from all three parent molecules show anti-structures relative to the carbonyl group for the low energy conformation where the radical sites are on the carbons and the nitrogen, not adjacent to the carbonyl. When the radical site is on the nitrogen atom adjacent to the carbonyl, all three radicals show that the syn conformer is the lowest energy structure.

3.3. Heats of Formation, Bond Energies, and Relative Stability of the Radicals Derived from the Target Parent Molecules

Four isodesmic reactions for each radical and the calculated standard enthalpies are listed in Table 3. The data illustrate excellent agreement across the different levels of calculations and through the different reaction analyses.
The enthalpies of formation of the parent molecules averaged over three work reactions for molecules CH3–C=ONHNH2, CH3–C=ONH2 and CH3–C=ONHCH3 were evaluated as −28.1, −57.29, and −56.53 kcal mol−1, respectively (values are average of B3LYP/6-31g(d,p), B3LYP/6-31g(2d,2p) and CBS-QB3 levels).

3.3.1. Enthalpy of Formation—Radicals

The four work reactions and calculated ΔHf°298 for use in determining the enthalpy of formation for each radical are shown in Table 3.
The recommended enthalpies of formation, in kcal mol−1, from the CBS-QB3 level calculations, averaged over four work reactions are:
(i)
Radicals from CH3–C=ONHNH2:
(a)
C•H2–C=ONHNH2 (19.27),
(b)
CH3–C=ON•NH2 (−2.07),
(c)
CH3–C=ONHN•H (1.60).
(ii)
Radicals from CH3–C=ONH2:
  • C•H2–C=ONH2 (−9.67),
  • CH3–C=ON•H (2.11).
(iii)
Radicals from CH3–C=ONHCH3
  • C•H2−C=ONHCH3 (−9.12),
  • CH3–C=ON•CH3 (−4.43),
  • CH3–C=ONHC•H2 (−15.39).

3.3.2. Bond Energies

Bond energies for the formation of radicals by loss of H atom reported at 298.15 K were calculated from the standard ΔHf°298 values of the parent molecules and of the radicals, obtained at CBS-QB3 level. ΔHf°298 of 52.1 kcal mol−1 was used for H atom enthalpy.
CH3–C=ONHNH2 → C•H2–C=ONHNH2 + H•
−28.14 19.27 52.01 kcal mol−1
ΔHrxn = [19.27 + 52.1] − [−28.14] = 99.51 kcal mol−1 = Bond Energy
The bond dissociation enthalpies of the radicals calculated at three different levels of theory are listed in Table 3. The largest difference in R–H bond energy for a given radical, considering the two DFT and the CBS-QB3 calculation methods and the four isodesmic reactions of each radical, was less than 1.5 kcal mol−1.
The bond dissociation energies for the C–H bonds in the methyl group adjacent to the carbonyl in CH3–C=ONHNH2 (99.51), CH3–C(=O)NH2 (99.72), and CH3–C=ONHCH3 (99.51) kcal mol−1 are in parentheses. These compare with the typical bond energy on a primary methyl site of a normal hydrocarbon of 101 kcal mol−1, and are ca. 2 kcal mol−1 lower. In contrast, they are ca. 3 kcal mol−1 higher than a typical primary methyl C–H bond on a ketone, which is 96 kcal mol−1. The C–H bond energy on the methyl group bonded to the amine to form the CH3–C=ONHC•H2 is 93.24 kcal mol−1.
The N–H bond strengths for nitrogen atom adjacent to the carbonyl groups in CH3–C=ONHNH2 (78.17), CH3–C(=O)NH2 (111.50), and CH3–C=ONHCH3 (104.19) kcal mol−1 are in the parenthesis. For comparison, the N–H bond in ammonia is (108), the CH3NH–H bond in methylamine is (102.4), and the NH2NH–H bond in hydrazine is (82) kcal mol−1.
The C–H bond strength in the CH3 group bonded to an amine in CH3–C=ONHCH2--H is 93.37 kcal mol−1 at the CBS-QB3 level. This compares with the C–H bond energy of H–CH2–NH2 (~94.4) in CH3NH2. This C–H bond in CH3–C=ONHC•H2 is 1 kcal mol−1 lower than on the methyl groups bonded to C=O.
The N–H bond of the N.H. group in CH3–C=O–N•–NH2 is the weakest in this molecule at 78.17 kcal mol−1, where the C–H bond in C•H2–C=ONHNH2 is 99.51 kcal mol−1, which is significantly higher. The N–H bond energy for acetohydrazide (CH3–C=ONHNH•) is markedly different at only 81.84 kcal mol−1. In the N–H bond cleavage of CH3–C=ON•NH2, the electrons from the radical site re-arrange to form a second double bond, from nitrogen to carbon. The N–H bond energy for CH3–C=ON•CH3 is 104.20 kcal mol−1 which is much higher than the CH3–C=ON•NH2.
The weakening of the N–H bonds in this hydrazide is essentially independent of the nature of the β-substituent (H, RCO, CO2Et, or PhSO2) and the stabilizing effect on the radical is brought about entirely by the three-electron on N–NH2 moiety [27].

3.4. Internal Rotor Potentials

Energy profiles for internal rotations about the C–C=O, O=C–N, N–C, and N–N bonds in the acetohydrazide, acetamide, and N-methyl acetamide were calculated to determine the lowest energy configurations, energies of the rotational conformers, and to identify the interconversion barriers between isomers. Torsional potentials were used to evaluate contributions to the entropy and heat capacity values when there were low barriers (less than 3.5 kcal mol−1) and internal rotation occurred.
The total energies as a function of the corresponding dihedral angles were computed at the B3LYP/6-31G(d,p) level of theory by scanning the torsion angles between 0° and 360° in steps of 15°, while all remaining coordinates were fully optimized. All potentials were rescanned when a lower energy conformer, relative to the initial low-energy conformer was found. The total energy of the corresponding most stable molecular conformer was arbitrarily set to zero and used as a reference point to plot the potential barriers. The resulting potential energy barriers for internal rotations in the stable nonradical and radical molecules are shown in Figure 3, Figure 4, Figure 5, Figure 6, Figure 7, Figure 8 and Figure 9. Dihedral angles obtained for the optimized lowest energy structures are shown in parentheses.
The CH3–C=O-NH-NH2 rotor is illustrated in Figure 3 for both the CH3–C=O–N(–H)—NH2 (H10–N9—N7–H8) and CH3–C(=O)—NH–NH2 (H8–N7—C5–O6) systems with barriers at 7.82 and 20.66 kcal mol−1, respectively. The CH3–C(=O)—NH–CH3 (H8–N7—C5–O6) rotor shows a two-fold symmetry with a barrier at 21.7 kcal mol−1. One reason for the high barriers for the rotation about the carbonyl (C=O)–NH bond involves the repulsive interaction of the carbonyl π bond with the NH lone pair.
The study of amide C–N rotation barriers is important for the evaluation of their reactivity, for input data in biochemical structure calculations other than finding the lowest energy conformer because the amide C–N bonds make up protein backbones. The amide conformations play an important role in enzyme structure and the barrier to the rotation affects the rigidity of that structure. The rigidity of an enzyme’s structure can affect its selectivity in binding substrates.
The C–N rotor for the radical C•H2–C(=O)—NH2 (H7–N6---C4–O5 is 15.97 kcal mol−1) and the value of its parent CH3–C(=O)—NH2 (H8–N7—C5–O6 is 18.66 kcal mol−1). According to Jasien et al. [12], based upon the current (DZ + d/SCF) calculations, the 0 K rotational barrier for acetamide between the C–N bond is predicted to be 12.5 kcal mol−1.
The two protons attached to N in acetamide are inequivalent at low temperatures but become averaged by C–N rotation at higher temperatures. Typical bond rotation barriers for amides in solution are experimentally determined by NMR to be between 17 and 22 kcal/mol. However, the acetamide enolate, [CH2CONH2] has a much lower barrier; according to NMR experiments, the enolate has free rotation at all accessible temperatures [28]. The HNCO anti/trans/Z configuration is significantly more probable in proteins than the syn/cis/E geometry. The ratio is 95:5 or even higher [29].
The CH3–C=O rotor for the CH3—C(=O)–NH2 (O6–C5—C1–H2) has a small barrier at 0.08 kcal mol−1 and shows three-fold symmetry The data are in reasonable agreement with the previous study conducted by J.R. Bailey [30], which also reported a low, calculated barrier monosubstituted N-methyl acetamide to be 0.21 kcal mol−1.
The CH3–C=O–HN—CH3 rotor is illustrated in Figure 6 which shows a three-fold symmetry with a barrier at 0.24 kcal mol−1.
The C(=O)NH2 rotor is illustrated in Figure 8 for both the C•H2–C(=O)—NH2 (H7–N6—C4–O5) and C•H2---C(=O)NH2 (O5–C4—C1–H2) systems with a great difference in bariers at 16.0 and 6.6 kcal mol−1, respectively, but with the same two-fold symmetry.
The CH3–C(=O)N•—CH3 (H9–C8—N7–C5) and CH3–C(=O)N—C•H2 (H10–C9—N7–H8) rotors are illustrated in Figure 9 and there is a significant difference in the internal rotor barriers. CH3–C(=O)N•—CH3 shows extremely low three-fold symmetry at 0.7 kcal mol−1, and CH3–C(=O)N—C•H2 shows two-fold symmetry at 8.7 kcal mol−1 barrier. The low barrier in CH3–C(=O)N•—CH3 is a result of the overlap between the carbonyl bond and the unpaired electron of the N atom, which reduces the interaction of the methyl H atoms with the N nitrogen π orbitals. The higher barrier for CH3–C(=O)N—C•H2 results from overlap (resonance) between the radical and the nitrogen π bonds.

3.5. Entropy and Heat Capacity

The entropy and heat capacity data for the parent molecules and their radicals as a function of temperature were determined from the optimized structures, moments of inertia, vibrational frequencies, symmetries, the known mass of the molecules, and internal rotor contributions when barriers were low. The calculations use standard formulas from statistical mechanics for the contributions of translation, external rotation, and vibrations [31,32]. Contributions to the entropy and the heat capacity from translation, vibrations, and external rotation were calculated using the SMCPS program. This program utilizes the rigid-harmonic oscillator approximation from the optimized structures obtained at B3LYP/6-31G(d,p) level. The number of optical isomers and the spin degeneracy of unpaired electrons is also incorporated for the calculation of S°298.
Contributions from hindered internal rotors to S°298 and Cp(T) are determined using the VIBIR program. This program utilizes the method of Pitzer and Gwinn [33,34], the potential barriers, folds, and moments of inertia from the internal rotor analysis. The moments of inertia were calculated. The rotors with a barrier value greater than 3.5 kcal mol−1 were treated as torsion vibrations. The internal rotor data were combined with the S(T) and Cp(T) data from frequencies, mass, moments of inertia, symmetry, and electronic degeneracy in the our statistical mechanics program SMCPS [35] and are presented in Table 4 for the parent molecules, Table 5 for radicals from acetic acid hydrazide, Table 6 for radicals from acetamide, and Table 7 for radicals from N-methyl acetamide.
Entropy and heat capacity contributions of the parent molecules and radicals using VIBIR have been calculated at temperatures ranging from 1–5000 K.

4. Summary

Thermochemical properties are presented for acetic acid hydrazide, Acetamide, N-methyl acetamide, and radicals that result from the loss of H atoms from the carbon and the nitrogen atoms. Standard enthalpies from all the work reactions and each of the calculation methods are in reasonably good agreement, suggesting that the B3LYP DFT calculations, in conjunction with the work reactions used here, are acceptable methods for larger hydrazide and amides. C–H bond energy values for the radicals C•H2–C=ONHNH2, C•H2–C=ONH2 and C•H2–C=ONHCH3 from the B3LYP/6-31G(d,p), B3LYP/6-31G(2d,2p) and CBS-QB3 levels of calculation were 99.50, 99.40, 99.61 and 100.22, 99.43, 99.52 and 99.54, 99.42, 99.56 kcal mol−1 respectively. The N–H bond in the acetohydrazide was weak, at 78.17 kcal mol−1, but strong in N-methyl acetamide at 104.20 kcal mol−1. The HN–H bond energies for the formation of the radicals CH3–C=ONHN•H and CH3–C=ON•H from the parent molecules were also similar across the different B3LYP basis sets and CBS-QB3 level of calculations (CH3–C=ONHN•H = 81.93, 81.45, 82.13; CH3-C=ON•H = 111.74, 110.76, 111.99 kcal mol−1) respectively.

Supplementary Materials

The following are available online at https://0-www-mdpi-com.brum.beds.ac.uk/2673-7264/1/1/2/s1. Table S1. CH3CONHNH2. Table S2. CH3CONH2. Table S3. CH3CONHCH3. Table S4. Moments of Inertia (amu bohr [2]). Table S5. Vibration Frequencies (cm−1). Table S6. Mulliken Atomic Charges for Acetohydrazide and its Radicals. Table S7. Mulliken Atomic Charges for Acetamide and its Radicals. Table S8. Mulliken Atomic Charges for N-Methyl Acetamide and its Radicals.

Author Contributions

Conceptualization, S.C. and J.W.B.; Formal analysis, S.C., and J.W.B.; Methodology, S.C., and J.W.B.; Software, J.W.B.; Writing-original draft, S.C.; Resources, S.C. and J.W.B.; Data Curations, S.C.; Writing-Review and Editing, S.C. and J.W.B.; Supervision, J.W.B. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Mennucci, B.; Martínez, J.M. How to model solvation of peptides? Insights from a quantum-mechanical and molecular dynamics study of N-methylacetamide. 1. Geometries, infrared, and ultraviolet spectra in water. J. Phys. Chem. B 2005, 109, 9818–9829. [Google Scholar] [CrossRef] [PubMed]
  2. Ataka, S.; Takeuchi, H.; Tasumi, M. Infrared studies of the less stable cis form of N-methylformmaide and N-methylacetamide in low temperature nitrogen matrices and vibrationa analyses of the trans and cis forms of these molecules. J. Mol. Struct. 1984, 113, 147–160. [Google Scholar] [CrossRef]
  3. Mayne, L.C.; Hudson, B. Resonance Rama Spectroscopy of N-methylacetamide: Overtones and combinations of the carbon-nitrogen stretch (aminde II) and effect of solvation on the carbon. J. Phys. Chem. 1991, 95, 2962. [Google Scholar] [CrossRef]
  4. Chen, X.G.; Schweitzerstenner, R.; Asher, S.A.; Mirkin, N.G.; Krimms, S. Vibrationals assignments of trans-N-methylacetamide and some of its deuterated isotopomers from band decomposition of IR, visible, and resonance Raman spectra. J. Phys. Chem. 1995, 99, 3074. [Google Scholar] [CrossRef]
  5. Torii, H.; Tasumi, T.; Tasumi, M. Effects of hydration on the structure, vibrational wavenumbers, vibrational force field and resonance raman intensities of N-methylacetamide. J. Raman Spectrosc. 1998, 29, 537. [Google Scholar] [CrossRef]
  6. Kubelka, J.; Keiderling, T.A. Ab Initio Calculation of Amide Carbonyl Stretch Vibrational Frequencies in Solution with Modified Basis sets.1. N-methylacetamide. J. Phys. Chem. A 2001, 105, 10922. [Google Scholar] [CrossRef]
  7. Cuevas, G.; Renugopalakrishnan, V.; Madrid, G.; Hagler, A.T. Density function studies of peptides Part I. Vibrational frequencies including isotopic effects and NMR chemical shifts of N-methylacetamide, a pedtide model from density fucntion and MP2 calculations. Phys. Chem. Chem. Phys. 2002, 4, 1490. [Google Scholar] [CrossRef]
  8. Papamokos, G.V.; Demetropoulos, I.N. Vibrational Frequencies of Amides and Amide Dimers: The Assessment of PW91XC Functional. J. Phys. Chem. A 2004, 108, 7291. [Google Scholar] [CrossRef]
  9. Zhang, R.; Li, H.R.; Lei, Y.; Han, S.J. Structures and interactions in N-methylacetamide-water mixtures studied by IR spectra and density functional theory. J. Mol. Struct. 2004, 693, 17. [Google Scholar] [CrossRef]
  10. Kaledin, A.L.; Bowman, J.M. Full Dimensional Quantum Calculations of Vibrationals Energies of N-methylacetamide. J. Phys. Chem. A 2007, 111, 5593–5598. [Google Scholar] [CrossRef] [PubMed]
  11. Badawi, H.M. Vibrational Spectra and analysis of acetohydrazide CH3–CO–NH–NH2. Spectrochim. Acta Part A Mol. Biomol. Spectrosc. 2007, 67, 592–597. [Google Scholar] [CrossRef]
  12. Jasien, P.G.; Stevens, W.J.; Krauss, M. Ab Initio calculations of the rotational barriers in formamide and acetamide: The effects of polarization functions and correlation. J. Mol. Struct. THEOCHEM 1986, 139, 197–206. [Google Scholar] [CrossRef]
  13. Zhou, Y.; Yang, Z.; Zhang, C.; Liu, X. Reaction mechanisms of DNT with hydroxyl radicals for advanced oxidation processes – DFT study. J. Mol. Modeling 2017, 23, 139. [Google Scholar] [CrossRef]
  14. Frisch, M.J.; Trucks, G.W.; Schlegel, H.B.; Scuseria, G.E.; Robb, M.A.; Cheeseman, J.R.; Zakrzewski, V.G.; Stratmann, J.A.; Montgomery, R.E., Jr.; Burant, J.C.; et al. Gaussian 98; Gaussian, Inc.: Pittsburgh, PA, USA, 1998. [Google Scholar]
  15. Frisch, M.J.; Trucks, G.W.; Schlegel, H.B.; Scuseria, G.E.; Robb, M.A.; Cheeseman, J.R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G.A.; et al. Gaussian 09; Gaussian, Inc.: Wallingford, CT, USA, 2009. [Google Scholar]
  16. Becke, A.D. Density-functional Thermochemistry. III. The Role of Exact Exchange. J. Chem. Phys. 1993, 98, 5648–5652. [Google Scholar] [CrossRef]
  17. Lee, C.; Yang, W.; Parr, R.G. Development of the Colle-Salvetti Correlation-Energy Formula Into a Functional of the Electron Density. Phys. Rev. B Condens. Matter Mater. Phys. 1988, 37, 785–789. [Google Scholar] [CrossRef]
  18. Purnell, D.L., Jr.; Bozzelli, J.W. Thermochemical Properties: Enthalpy, Entropy, and Heat Capacity of C2-C3 Fluorinated Aldehydes. Radicals and Flurocarbon Group Additivity. J. Phys. Chem. A 2019, 123, 650–665. [Google Scholar] [CrossRef]
  19. Montgomery, J.A.; Frisch, M.J.; Ochterski, J.W.; Petersson, G.A. A Complete Basis Set Model Chemistry. VII. Use of the Minimum Population Localization Method. J. Chem. Phys. 2000, 112, 6532–6542. [Google Scholar] [CrossRef]
  20. Zhu, L.; Bozzelli, J.W. The multi-channel reaction of CH3S+ 3O2: Thermochemistry and Kinetik barriers. J. Mol. Struct. THEOCHEM 2005, 728, 147–157. [Google Scholar] [CrossRef]
  21. NIST Chemistry WebBook. Standard Reference Database No. 69. In February 2000. Available online: http://webbook.nist.gov/chemistry/.NIST (accessed on 15 April 2011).
  22. Dorofeeva, O.V.; Ryzhova, O.N.; Suchkova, T.A. Enthalpies of Formation of Hydrazine and Its Derivatives. J. Phys. Chem. A 2017, 121, 5361. [Google Scholar] [CrossRef] [PubMed]
  23. Pedley, J.B. Thermochemical Data and Structures of Organic Compounds; Thermodynamics Research Center: College Station, TX, USA, 1994; Volume I. [Google Scholar]
  24. Anderson, W.R. Oscillator strengths of amidogen and the heats of formation of imidogen and amidogen. J. Phys. Chem. 1989, 93, 530–536. [Google Scholar] [CrossRef]
  25. Wang, H.; Castillo, A.; Bozzelli, J.W. Thermochemical Properties Enthalpy, Entropy, and Heat Capacity of C1-C4 Fluorinated Hydrocarbons: Flurocarbon Group Additivity. J. Phys. Chem. A 2015, 119, 8202–8215. [Google Scholar] [CrossRef]
  26. Ruscic, B. ATcT Enthalpies of Formation Based on Version 1.112 of the Thermochemical Network. Available online: http://atct.anl.gov/Thermochemical_Data/version_1.112/ (accessed on 15 April 2011).
  27. Zhao, Y.; Frederick; Bordwell, G.; Cheng, J.-P.; Wang, D. Equilibrium Acidities and Homolytic Bond Dissociation Energies (BDEs) of the Acidic H-N Bonds in the Hydrazines and Hydrazides. J. Am. Chem. Soc. 1997, 119, 9125–9129. [Google Scholar] [CrossRef]
  28. Richard, J.; Williams, G.; O’Donoghu, A.; Amyes, T.L. Formation and Stability of Enolates of Acetamide and Acetate Anion: An Eigen Plot for Proton Transfer at alpha-Carbonyl Carbon. J. Am. Chem. Soc. 2002, 124, 2957–2968. [Google Scholar] [CrossRef]
  29. Ledneczki, I.; Forgo, P.; Kiss, J.T.; Molnar, A.; Palinko, I. Conformational behavious of acetamide derivatives studies by NMR spectroscopic and computational methods. J. Mol. Struct. 2007, 834–836, 349–354. [Google Scholar] [CrossRef]
  30. Bailey, J.R.; McMahon, T.J.; Bird, R.G. Dyanamics of peptide bonds: A study of N-methylethanolamine using chirped-pulsed Fourier transform microwave spectroscopy. J. Mol. Spectrosc. 2017, 335, 33–36. [Google Scholar] [CrossRef]
  31. Asatryan, R.; Bozzelli, J.W.; Simmie, J.M. Thermochemistry for enthalpies and reaction paths for nitrous acid isomers. Int. J. Chem. Kinet. 2007, 39, 378–398. [Google Scholar] [CrossRef]
  32. Sun, H.; Bozzelli, J.W. Structures, Intramolecular Rotation Barriers, and Thermochemical Properties of Radicals Derived from H Atom Loss in Mono-, Di-, and Trichloromethanol and Parent Chloromethanols. J. Phys. Chem. A 2001, 105, 4504–4516. [Google Scholar] [CrossRef]
  33. Pitzer, K.S. Thermochemistry and bond energies of nitro-alkanes, -alkenes, -carbonyls and corresponding nitrites. J. Chem. Phys. 1937, 5, 469. [Google Scholar] [CrossRef]
  34. Pitzer, K.S.; Gwinn, W.D. Energy levels and thermodynamic functions for molecules with internal rotation I. Rigid frame with attached tops. J. Chem. Phys. 1942, 10, 428. [Google Scholar] [CrossRef]
  35. Sheng, C. Elementary, Pressure Dependent Model for Combustion of C1, C2 and Nitrogen Contaninig Hydrocarbons: Operation of a Pilot Scale Incinerator and Model Comparison. Ph.D. Thesis, Chemical Engineering, New Jersey Institute of Technology, Newark, NJ, USA, 2002. [Google Scholar]
Figure 1. Optimized structures of the parent molecules (CH3–C=ONHNH2, CH3–C=ONH2, and CH3–C=ONHCH3) at B3LYP/6-31G(d,p) level. All show the nitrogen bonded to the carbonyl in a sp2 configuration.
Figure 1. Optimized structures of the parent molecules (CH3–C=ONHNH2, CH3–C=ONH2, and CH3–C=ONHCH3) at B3LYP/6-31G(d,p) level. All show the nitrogen bonded to the carbonyl in a sp2 configuration.
Thermo 01 00002 g001aThermo 01 00002 g001b
Figure 2. Optimized structures of the radicals at B3LYP/6-31G(d,p) level.
Figure 2. Optimized structures of the radicals at B3LYP/6-31G(d,p) level.
Thermo 01 00002 g002aThermo 01 00002 g002b
Figure 3. Potential energy barriers for internal rotations about N–N and O=C–N bonds in CH3–C=O–NH–NH2 and CH3–C=O–NH–CH3.
Figure 3. Potential energy barriers for internal rotations about N–N and O=C–N bonds in CH3–C=O–NH–NH2 and CH3–C=O–NH–CH3.
Thermo 01 00002 g003
Figure 4. Potential energy barriers for internal rotations about O=C–N single bond in acetamide.
Figure 4. Potential energy barriers for internal rotations about O=C–N single bond in acetamide.
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Figure 5. Potential energy barriers for internal rotations about C–C=O single bond in acetamide.
Figure 5. Potential energy barriers for internal rotations about C–C=O single bond in acetamide.
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Figure 6. Potential barriers for internal rotations about N–C bond in N-methyl acetamide.
Figure 6. Potential barriers for internal rotations about N–C bond in N-methyl acetamide.
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Figure 7. Potential barriers for internal rotations about N•—N bond in radical CH3–C=ON•—NH2 which shows a two-fold symmetry with a barrier at 14.6 kcal mol−1.
Figure 7. Potential barriers for internal rotations about N•—N bond in radical CH3–C=ON•—NH2 which shows a two-fold symmetry with a barrier at 14.6 kcal mol−1.
Thermo 01 00002 g007
Figure 8. Potential barriers for internal rotations about O=C–N and C•–C=O bond in acetamide radical C•H2–C(=O) NH2.
Figure 8. Potential barriers for internal rotations about O=C–N and C•–C=O bond in acetamide radical C•H2–C(=O) NH2.
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Figure 9. Potential barriers for internal rotations about N•—C and N—C• bond in CH3–C(=O)N•—CH3 and CH3–C(=O)N—C•H2.
Figure 9. Potential barriers for internal rotations about N•—C and N—C• bond in CH3–C(=O)N•—CH3 and CH3–C(=O)N—C•H2.
Thermo 01 00002 g009
Table 1. Standard enthalpies of formation of reference species at 298.15 K.
Table 1. Standard enthalpies of formation of reference species at 298.15 K.
SpeciesΔHf°298 (kcal mol−1)Reference No.
CH3NHNH222.6NIST [21]
CH3CONH2−56.96 ± 0.19
CH3CH3−20.04 ± 0.1
CH3CH2CH3−25.02 ± 0.12
NH2CONH2−56.29 ± 0.29
CH3COCH3−52.23 ± 0.14
NH2CH2CO2H−93.3 ± 1.1
CH3CH2OH−56 ± 0.5
CH3CO2H−103.5 ± 0.6
CH3C∙HCH322.5 ± 0.5
NH3−10.98 ± 0.084
NH2N∙H52.74
C∙H2NH236.69
CH3N∙H44.84
NH2NH223.18Dorofeeva [22]
CH3CH2NH2−11.35 ± 0.14Pedley [23]
N∙H244.5Anderson [24]
CH3OH−47.97 ± 3Bozzelli [25]
C∙H2CHO4.4 ± 0.84ATcT [26]
CH3C∙HOH−13.2 ± 0.61
C∙H2OH−3.9 ± 0.33
CH3CHO−39.9 ± 0.28
CH3C∙H228.6 ± 0.28
CH3NH2−4.6
Table 2. Enthalpies of reaction at 298 K and calculated enthalpies of formation (ΔHf°298) of parent molecules.
Table 2. Enthalpies of reaction at 298 K and calculated enthalpies of formation (ΔHf°298) of parent molecules.
CH3CONHNH2 Units: (kcal mol−1)B3LYP/631G(d,p)B3LYP/6-31G(2d,2p)CBS-QB3
CH3CONHNH2 + CH3NH2 → CH3NHNH2 + CH3CONH2−29.43−30.57−29.51
CH3CONHNH2 + CH3CH2OH → CH3CH2NH2 + NH2CH2CO2H−26.45−26.10−25.29
CH3CONHNH2 + CH3CHO → NH2CONH2 + CH3COCH3−29.61−29.56−26.44
Standard Enthalpy—Average−28.50−28.74−27.08
CH3CONH2
CH3CONH2+CH3CH2OH→ CH3COOH+ CH3CH2NH2−56−55.13−56.63
CH3CONH2+CH3CH3→CH3COCH3+ CH3NH2−58.46−57.08−55.90
CH3CONH2+CH3NH2→ CH3NHNH2 + CH3CHO−58.72−58.30−59.66
Standard Enthalpy—Average−57.73−56.84−57.40
CH3CONHCH3
CH3CONHCH3 + CH3NH2 → CH3CONH2 + CH3CH2NH2−55.31−56.04−55.05
CH3CONHCH3 + CH3NH2 → CH3COCH3 + CH3NHNH2−57.42−57.53−57.31
CH3CONHCH3 + NH2NH2 → CH3CONH2 + CH3NHNH2−55.85−57.22−57.08
Standard Enthalpy—Average−56.19−56.93−56.48
Table 3. Calculated standard enthalpies of formation (ΔHf°298) of radicals and R–H bond energies.
Table 3. Calculated standard enthalpies of formation (ΔHf°298) of radicals and R–H bond energies.
Radical C•H2CONHNH2 Units: (kcal mol−1)B3LYP/6-31G(d,p)B3LYP6-31G(2d,2p)CBS-QB3
C•H2CONHNH2 + CH3OH → CH3CONHNH2 + C•H2OH18.9619.1419.13
C•H2CONHNH2 + CH3NH2 → CH3CONHNH2 + C•H2NH218.1418.0918.76
C•H2CONHNH2 + CH3CHO → CH3CONHNH2 + C•H2CHO19.9419.7819.94
C•H2CONHNH2 + CH3CH2CH3 → CH3CONHNH2 + CH3C•HCH320.0219.6319.67
Standard Enthalpy—Average19.2619.1619.37
Bond Energy H—CH2CONHNH299.5099.4099.61
Radical CH3CON•NH2
CH3CON•NH2 + CH3NH2 → CH3CONHNH2 + CH3N•H−0.32−0.06−0.52
CH3CON•NH2 + NH2NH2 → CH3CONHNH2 + NH2N•H−2.39−2.71−2.68
CH3CON•NH2 + NH3 → CH3CONHNH2 + N•H2−2.40−2.11−2.02
CH3CON•NH2 + CH3CH2OH → CH3CONHNH2 + CH3C•HOH−3.93−3.24−2.41
Standard Enthalpy—Average−2.26−2.03−1.91
Bond Energy CH3CO(N—H)NH277.9878.2178.33
Radical CH3CONHN•H
CH3CONHN•H + CH3NH2 → CH3CONHNH2 + CH3N•H3.633.183.28
CH3CONHN•H + NH2NH2 → CH3CONHNH2 + NH2N•H1.560.531.12
CH3CONHN•H + NH3 → CH3CONHNH2 + N•H21.551.121.78
CH3CONHN•H + CH3CH2OH → CH3CONHNH2 + CH3C•HOH0.0201.40
Standard Enthalpy—Average1.691.211.89
Bond Energy CH3CONHHNH—H81.9381.4582.13
Radical C•H2CONH2
C•H2CONH2 + CH3OH → CH3CONH2 + C•H2OH−9.48−9.97−10.12
C•H2CONH2 + CH3NH2 → CH3CONH2 + C•H2NH2−10.29−11.03−10.49
C•H2CONH2 + CH3CHO → CH3CONH2 + C•H2CHO−8.50−9.33−9.31
C•H2CONH2 + CH3CH2CH3 → CH3CONH2 + CH3C•HCH3−8.42−9.49−9.57
Standard Enthalpy—Average−9.17−9.96−9.87
Bond Energy H—CH2CONH2100.2199.4399.52
Radical CH3CON•H
CH3CONH• + CH3NH2 → CH3CONH2 + CH3N•H4.293.343.99
CH3CONH• + NH2NH2 → CH3CONH2 + NH2N•H2.220.691.83
CH3CONH• + NH3 → CH3CONH2 + N•H22.211.292.49
CH3CONH• + CH3CH2OH → CH3CONH2 + CH3C•HOH0.680.162.10
Standard Enthalpy—Average2.351.372.60
Bond Energy CH3CONH—H111.74110.76111.99
Radical C•H2CONHCH3
C•H2CONHCH3 + CH3OH → CH3CONHCH3 + C•H2OH−9.40−9.23−9.31
C•H2CONHCH3 + CH3NH2 → CH3CONHCH3 + C•H2NH2−10.21−10.29−9.69
C•H2CONHCH3 + CH3CHO → CH3CONHCH3 + C•H2CHO−8.42−8.59−8.51
C•H2CONHCH3 + CH3CH2CH3 → CH3CONHCH3 + CH3C•HCH3−8.34−8.74−8.77
Standard Enthalpy—Average−9.10−9.21−9.07
Bond Energy H—CH2CONHCH399.5499.4199.56
Radical CH3CON•CH3
CH3CON•CH3+CH3NH2 → CH3CONHCH3 + CH3N•H−2.81−2.92−2.27
CH3CON•CH3 + NH2NH2 → CH3CONHCH3 + NH2NHJ−4.88−5.57−4.43
CH3CON•CH3+NH3 → CH3CONHCH3 + NH2J−4.89−4.97−3.77
CH3CON•CH3 + CH3CH2OH → CH3CONHCH3 + CH3C•HOH−6.42−6.10−4.15
Standard Enthalpy—Average−4.75−4.89−3.65
Bond Energy CH3CON—HCH3103.88103.74104.98
Radical CH3CONHC•H2
CH3CONHC•H2 + CH3OH → CH3CONHCH3 + C•H2OH−15.58−15.64−15.50
CH3CONHC•H2 + CH3NH2 → CH3CONHCH3 + C•H2NH2−16.39−16.70−15.88
CH3CONHC•H2 + CH3CHO → CH3CONHCH3 + C•H2CHO−14.60−15−14.70
CH3CONHC•H2 + CH3CH2CH3 → CH3CONHCH3 + CH3C•HCH3−14.52−15.15−14.96
Standard Enthalpy—Average−15.27−15.62−15.26
Bond Energy CH3CONHCH2—H93.3693.0193.37
Table 4. Ideal gas-phase thermodynamic property vs. temperature a of parent molecules.
Table 4. Ideal gas-phase thermodynamic property vs. temperature a of parent molecules.
T (K)ΔHf°298 kcal mol−1CH3CONHNH2ΔHf°298 kcal mol−1CH3CONH2ΔHf°298 kcal mol−1CH3CONHCH3
Cp(T)S°(T)Cp(T)S°(T)Cp(T)S°(T)
1−28.587.94916.841−58.147.94914.636−56.547.94914.677
518.87748.2688.83146.0398.53245.934
10110.85154.9999.83552.51210.15552.332
15113.15459.8211.16156.72912.07156.795
20115.60963.93212.86660.16314.23760.555
25118.09867.67614.71963.22716.5763.973
29821.57571.05217.53965.96221.06567.078
40026.41777.76321.31171.35726.21573.371
50030.64883.88124.61376.24530.96179.271
60034.24989.627.43480.835.11884.912
70036.27594.94928.83285.05436.67790.28
80039.88199.9631.8889.03641.77895.376
90041.108104.66532.66392.77442.417100.209
100044.052109.09435.2196.29446.735104.794
110044.75113.27535.57699.61646.733109.148
120046.236117.2336.772102.76148.481113.287
130047.54120.9837.824105.74450.005117.225
140048.686124.54338.751108.57951.337120.977
150050.695127.93440.562111.27954.499124.556
200053.236142.75742.451123.0956.539140.262
250055.241154.86644.091132.75158.785153.137
300056.455165.0545.088140.88260.132163.98
350057.235173.81445.73147.88360.992173.316
400057.763181.49246.164154.01861.572181.499
450058.135188.31746.471159.47361.979188.775
500058.407194.45646.695164.38162.276195.321
a Thermodynamic properties refer to the standard state of an ideal gas at 1 atm. S°(T) and C°p(T) in cal mol−1 K−1.
Table 5. Ideal gas-phase thermodynamic property vs. temperature a of radicals of parent CH3CONHNH2.
Table 5. Ideal gas-phase thermodynamic property vs. temperature a of radicals of parent CH3CONHNH2.
T (K)ΔHf°298 kcal mol−1C∙H2–C=ONHNH2ΔHf°298 kcal mol−1CH3–C=ON∙NH2ΔHf°298 kcal mol−1CH3–C=ONHN∙H
Cp(T)S°(T)Cp(T)S°(T)Cp(T)S°(T)
119.117.94920.227−2.087.94917.9011.587.94918.037
519.56152.3788.89949.3188.19749.18
10111.59959.55110.97656.1099.83855.307
15114.39464.76513.1660.96512.07259.701
20117.26569.29415.36665.04714.49463.498
2512073.43617.56868.70716.91266.986
29822.45777.15521.53271.96720.27670.145
40027.09384.42225.64278.36724.78976.43
50030.84990.87629.26884.13828.66182.147
60033.90696.77232.37289.49631.91987.474
70036.419102.18733.73894.48233.63392.442
80038.53107.18637.21999.13536.95497.082
90040.338111.82637.971103.48837.923101.427
100041.907116.15540.787107.57340.63105.509
110043.28120.21241.12111.41941.111109.353
120044.486124.02742.395115.0542.399112.984
130045.549127.62843.509118.48543.524116.42
140046.487131.03644.484121.74444.507119.68
150047.315134.2746.4124.8446.368122.778
200050.25148.31748.328138.32948.364136.276
250051.93159.72250.009149.30650.041147.261
300052.953169.28551.023158.51751.05156.478
350053.614177.551.674166.43351.696164.398
400054.062184.68952.114173.36352.132171.33
450054.379191.07552.424179.51952.439177.488
500054.61196.81652.65185.05452.662183.025
a Thermodynamic properties refer to the standard state of an ideal gas at 1 atm. S°(T) and C°p(T) in cal mol−1 K−1.
Table 6. Ideal gas-phase thermodynamic property vs. temperature a of radicals of parent CH3CONH2.
Table 6. Ideal gas-phase thermodynamic property vs. temperature a of radicals of parent CH3CONH2.
T (K)ΔHf°298 kcal mol−1C•H2–C=ONH2ΔHf°298 kcal mol−1CH3–C=ON•H
Cp(T)S°(T)Cp(T)S°(T)
1−10.237.94917.9661.687.94915.81
518.02949.0737.95246.907
1019.42254.9698.38652.495
15111.76659.2149.78156.132
20114.19862.92811.55459.18
25116.45966.33713.40461.952
29818.43269.39316.1864.453
40022.02475.33219.76169.423
50024.84880.55422.80273.938
60027.12185.28625.33178.138
70028.98589.60726.43982.046
80030.55593.57829.21285.691
90031.90797.25429.73389.1
100033.088100.67532.03992.299
110034.126103.87532.17995.309
120035.043106.88233.16798.15
130035.854109.71834.028100.837
140036.573112.434.78103.385
150037.21114.94436.434105.806
200039.482125.98537.724116.342
250040.794134.94538.998124.906
300041.597142.45739.763132.087
350042.117148.9140.252138.255
400042.47154.55740.582143.652
450042.72159.57440.814148.445
500042.902164.08540.983152.754
a Thermodynamic properties refer to the standard state of an ideal gas at 1 atm. S°(T) and C°p(T) in cal mol−1 K−1.
Table 7. Ideal gas-phase thermodynamic property vs. temperature a of radicals of parent CH3CONHCH3.
Table 7. Ideal gas-phase thermodynamic property vs. temperature a of radicals of parent CH3CONHCH3.
T (K)ΔHf°298 kcal mol−1C∙H2–C=ONHCH3ΔHf°298 kcal mol−1CH3–C=ON∙CH3ΔHf°298 kcal mol−1CH3–C=ONHC•H2
Cp(T)S°(T)Cp(T)S°(T)Cp(T)S°(T)
1−8.857.94918.06−4.027.94915.856−15.117.94918.072
518.76249.4158.61947.1549.37249.785
10110.95156.11810.26853.6211.97357.054
15113.53161.03412.06158.11414.5862.399
20116.13765.27913.9761.83717.07366.931
25118.68569.14716.0665.1719.50670.996
29822.11572.62821.36768.16822.90774.613
40026.98779.51825.82974.19927.57781.691
50031.21785.7729.98879.81231.65488.051
60034.80891.59633.63385.14835.12993.943
70036.84197.03434.44690.20237.05699.42
80040.427102.1239.43494.97940.587104.531
90041.654106.8939.55299.49341.755109.315
100044.584111.37643.74103.76344.654113.81
110045.266115.60643.342107.80645.306118.046
120046.732119.60544.863111.6446.754122.048
130048.014123.39446.182115.28148.023125.838
140049.136126.99147.329118.74349.136129.435
150051.118130.41350.395122.04151.114132.857
200053.55145.34351.759136.45753.532147.783
250055.472157.51353.646148.22455.455159.949
300056.629167.73454.77158.10956.615170.167
350057.37176.52155.485166.60857.358178.952
400057.87184.21555.965174.04957.86186.645
450058.221191.05256.302180.6658.214193.48
500058.478197.19956.547186.60558.471199.627
a Thermodynamic properties refer to the standard state of an ideal gas at 1 atm. S°(T) and C°p(T) in cal mol−1 K−1.
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