Olga V. Dorofeeva

Thermodynamic Properties of Twenty‐One Monocyclic Hydrocarbons

The available structural parameters, fundamental frequencies, and relative energies of different stable conformers, if any, for cyclopropane, cyclopropene, cyclobutane, cyclobutene, 1,3‐cyclobutadiene, cyclopentane, cyclopentene, 1,3‐cyclopentadiene, cyclohexane, cyclohexene, 1,3‐cyclohexadiene, 1,4‐cyclohexadiene, cycloheptane, cycloheptene, 1,3‐cycloheptadiene, 1,3,5‐cycloheptatriene, cyclooctane, cyclooctene, 1,3‐cyclooctadiene, 1,5‐cyclooctadiene, and 1,3,5,7‐cyclooctatetraene were critically evaluated and the recommended values selected. Molecular constants for some molecules were estimated as the experimental values for these compounds are not available. This information was utilized to calculate the ideal gas thermodynamic properties C○p, S○, −(G○−H○0)/T, H○−H○0, and log Kf from 100 to 1500 K. The thermal functions were obtained using the rigid‐rotor harmonic‐oscillator approximation. The contributions derived for the inversion motion of cyclobutane and cyclopentene were obtained from energy levels...

NIST-JANAF Thermochemical Tables. II. Three Molecules Related to Atmospheric Chemistry: HNO3, H2SO4, and H2O2

The structural, spectroscopic, and thermochemical properties of three polyatomic molecules with internal rotation—HNO3(g), H2SO4(g), and H2O2(g)—have been reviewed. Three revised ideal gas thermodynamic tables result from this critical examination. The revisions involved the consideration of new spectroscopic information and the use of theoretical results to model the internal rotation in the H2SO4 molecule. Compared to previous calculations, the entropies at 298.15 K are unchanged for HNO3 and H2O2, but the high temperature values (T>4000 K) are significantly different. As for H2SO4, its thermodynamic functions differ significantly from values calculated earlier.

NIST-JANAF Thermochemical Tables. I. Ten Organic Molecules Related to Atmospheric Chemistry

The structural, spectroscopic, and thermodynamic properties of 10 gas phase organic molecules related to atmospheric chemistry, including three peroxides and four carboxylic acids, are reviewed. The calculation of the thermochemical tables involved the critical evaluation of new spectroscopic data, enthalpy of formation determinations, and the use of recent internal rotation data. Since insufficient information to characterize all 10 molecules exists, estimation schemes were used to provide the missing experimental and theoretical data.

Ideal gas thermodynamic properties of oxygen heterocyclic compounds Part 1. Three-membered, four-membered and five-membered rings

Abstract The available structural parameters, fundamental frequencies and enthalpies of formation for oxirane, oxirene, dioxirane, oxetane, 1,2-dioxetane, tetrahydrofuran, 2,3-dihydrofuran, 2,5-dihydrofuran, furan, 1,2-dioxolane, 1,3-dioxolane, 1,2,3-trioxolane and 1,2,4-trioxolane were critically evaluated and recommended values were selected. Molecular constants and enthalpies of formation for some of the molecules were estimated, as experimental values for these compounds are not available. Using the rigid-rotor harmonic-oscillator approximation, this information was used to calculate the chemical thermodynamic functions CpXXX, SXXX, − ( G XXX − H 0 XXX ) T , HXXX it- HXXX0, and the properties of formation, ΔfHXXX, ΔfGXXX, log KfXXX, to 1500 K in the ideal gas state at a pressure of 1 bar. The contributions to the thermodynamic properties of compounds having inversion motion (oxetane, 2,3- and 2,5-dihydrofuran) or pseudo-rotation (tetrahydrofuran and 1,3-dioxolane) have been computed by employing a partition function formed by the summation of the inversional or pseudo-rotational energy levels. These energy levels have been calculated by solving the wave equation using appropriate potential functions. The calculated values of the thermodynamic functions are compared with those reported in other works. Comparison with experimental data, where such are available, is also presented. The thermodynamic properties for seven of the compounds are reported for the first time.

Electron diffraction determination of the vapour phase molecular structure of azetidine, (CH2)3NH

Abstract The electron diffraction study of azetidine yielded the following main geometrical parameters ( r a structure): dihedral angle (the angle between the C-C-C and C-N-C planes) φ = 33.1 ± 2.4°, r (C-N) = 1.482 ± 0.006A, r (C-C) = 1.553 ± 0.009A, r (C-H) = 1.107 ± 0.003A, ∠C-N-C = 92.2 ± 0.4°, ∠C-C-C = 86.9 ± 0.4° and ∠C-C-N = 85.8 ± 0.4°.

Molecular Structure of 9H-Adenine Tautomer: Gas-Phase Electron Diffraction and Quantum-Chemical Studies

Molecular geometry of 9H-adenine tautomer was calculated by MP2 method using several basis sets (up to cc-pVQZ). According to the results of all quantum-chemical calculations, the molecule has an essentially planar heavy-atom skeleton and a quasi-planar amino group. Since the bond lengths of adenine are of similar magnitude, the structural problem could not be solved by the gas-phase electron diffraction (GED) method alone. Therefore the differences between similar bond lengths derived from ab initio geometry and rotational constants from microwave (MW) spectroscopic study (Brown, R. D.; et al. Chem. Phys. Lett. 1989, 156, 61) were used as supplementary data. To bring the data of the different experimental methods to the same basis (equilibrium structure), GED internuclear distances r(a) and MW rotational constants B(0)((i)) (i = A, B, C) were corrected for vibrational effects. Harmonic and anharmonic corrections were estimated using quadratic and cubic force constants from MP2/cc-pVTZ calculations. Anharmonic corrections to r(a) distances were calculated using improved theoretical approximation. The molecular structure of 9H-adenine is determined experimentally for the first time. Since the GED intensities are not sensitive to hydrogen positions, and small deviations of skeleton cannot be determined with appropriate uncertainty, the molecular configuration of adenine was assumed to be planar (C(s) symmetry) in the GED analysis. The main equilibrium structural parameters determined from GED data supplemented by rotational constants and results of MP2/cc-pVTZ calculations are the following (bond lengths in angstroms and bond angles in degrees with 3sigma in parentheses): r(e)(C2-N1) = 1.344(3), r(e)(C2-N3) = 1.330(3), r(e)(C4-N3) = 1.333(3), r(e)(C4-C5) = 1.401(3), r(e)(C5-C6) = 1.409(3), r(e)(C6-N1) = 1.332(3), r(e)(C5-N7) = 1.380(4), r(e)(C8-N7) = 1.319(3), r(e)(C8-N9) = 1.371(4), r(e)(C4-N9) = 1.377(4), r(e)(C6-N10) = 1.357(4), angle(e)(N1-C2-N3) = 129.0(1), angle(e)(C2-N3-C4) = 111.0(1), angle(e)(N3-C4-C5) = 127.2(1), angle(e)(C4-C5-N7) = 111.9(2), angle(e)(C5-N7-C8) = 103.4(2), and angle(e)(C5-C6-N10) = 121.9(2). The determined experimental bond lengths of adenine are in good agreement with those from MP2 calculations and with experimental bond lengths of pyrimidine and 1H-imidazole (except for the C-C double bond in imidazole). Being close to typical aromatic internuclear distances, the obtained C-C and C-N bond lengths indicate the aromatic nature of this molecule. The calculated aromaticity indexes (GIAO-MP2/cc-pVTZ) confirm this statement.

Density functional theory study of conformations, barriers to internal rotations and torsional potentials of polychlorinated biphenyls

Abstract Torsional barriers, potential energy curves, structural parameters and vibrational frequencies were calculated for 119 polychlorinated biphenyls (PCBs) at the B3LYP/6-31G(d,p) density functional theory level. From these calculations, the molecular parameters of remaining 90 PCB congeners can be estimated with reasonable accuracy. The conformations and torsional barriers of PCBs are mainly determined by the number of ortho chlorine atoms, while the meta chlorine atoms have a small influence on the torsional angles and barriers. All 209 PCBs were sorted into 18 groups depending on the number of ortho and adjacent meta substituents. In each group the internal rotation behavior of PCB congeners is very similar. For PCBs with 2–4 ortho chlorine atoms, the calculated barrier heights are 10–80 kJ/mol higher than those determined earlier by semiempirical AM1 method.

An electron diffraction study of 3-methyldiaziridine and 1,2-dimethyldiaziridine

Abstract The structures of the title compounds, diaziridines, (the first to be studied in the gas phase) have been determined by electron diffraction. The following principal structural parameters were obtained with the estimated standard deviations parenthesized: 3-methyldiaziridine, N-C = 1.489(9) A, N-N = 1.444(13) A, C-C = 1.505(16) A, C-H = 1.107(5) A, α =∠ (C-C, NCN) = 61.3° (0.9); 1,2-dimethyldiaziridine, (parameters of the cycle CN 2 were assumed from the previous molecule), N-C (methyl) = 1.445(3) A, C-H = 1.108(9) A, ∠ C-N-Me = 112.0° (0.5), the two methyl groups are in the trans position. Vibrational amplitudes were also determined for all important distances.

An electron diffraction study of the molecular structure of gaseous bicyclo[3.3.1]nonane

Abstract A gas-phase electron diffraction study of the title compound, carried out at 65°C, has found no statistically significant evidence for the presence of any conformer other than the double chair. The geometrical parameters were found to be: r g (CC) av = 1.538(1) A, r g (CH) av = 1.116(3) A, ∠C1C9C5 = 111.5(1.1)°, ∠C2C3C4 = 111.2(1.4)°, ∠HCH = 107.0(2.6)°, ∠θ = 121.5(0.8)°, ∠ϕ = 42.6(2.5)°. In an attempt to refine electron diffraction data for models with three non-equivalent CC distances, two sets of molecular parameters were obtained. Amplitudes of vibration were calculated from an approximate force field and the uncertainties in the fixed amplitudes were analyzed. The resulting structural parameters, chosen on the basis of molecular mechanical calculations, were: ( r g structure for bond lengths, r α structure for angles) C1C2 = 1.559(10) A, C2C3 = 1.541(10) A, C1C9 = 1.480(9) A, CH = 1.114(3) A, ∠C1C9C5 = 110.1(2.3)°, ∠C2C3C4 = 113.2(2.7)°, ∠HCH = 111.4(3.5)°, ∠θ = 124.1(0.9), ∠ϕ = 40.0(2.0)°. Comparison with structures of other bicyclo[ n.m. 1]alkanes has been made.

Ideal gas thermodynamic properties of oxygen heterocyclic compounds: Part 2. Six-membered, seven-membered and eight-membered rings

Abstract The available structural parameters, fundamental frequencies and enthalpies of formation for tetrahydro-2 H -pyran, 3,4-dihydro-2 H -pyran, 3,6-dihydro-2 H -pyran, 1,3-dioxane, 1,4-dioxane, 3,6-dihydro-1,2-dioxin, 2,3-dihydro-1,4-dioxin, 1,4-dioxin, 1,3,5-trioxane, oxepane, oxepin, 1,3-dioxepane, 4,7-dihydro-1,3-dioxepin, oxocane, 1,3-dioxocane, 1,3,6-tri-oxocane and 1,3,5,7-tetraoxocane were critically evaluated and the recommended values were selected. Molecular constants and enthalpies of formation for some of the molecules were estimated, because experimental values for these compounds were not available. Using the rigid-rotor harmonic-oscillator approximation, this information was utilized to calculate the chemical thermodynamic functions C ° p , S °, −( G ° − H ° 0 )/ T and H ° − H ° 0 and the properties of formation Δ f H °, Δ f G ° and log K ° f to 1500 K in the ideal gas state at a pressure of 1 bar. The contributions to the thermodynamic properties of 1,4-dioxin undergoing inversion motion have been computed by employing a partition function formed by the summation of the inversional energy levels. These energy levels were calculated by solving the wave equation using a potential function of type V ( x ) = ax 4 + bx 2 . The calculated values of the thermodynamic functions are compared with those reported in other work. Agreement with experimental data, where such are available, is satisfactory within the experimental uncertainties. Thermodynamic properties for 13 compounds are reported for the first time.