共查询到20条相似文献,搜索用时 46 毫秒
1.
V. N. Emel’yanenko S. P. Verevkin E. N. Burakova G. N. Roganov M. K. Georgieva 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2009,83(4):598-603
The enthalpies of formation of γ-pentanolactone (I), γ-hexanolactone (II), and γ-nonanolactone (III) were determined by combustion calorimetry. The enthalpies of vaporization of these lactones were measured by the transfer method. Conformational analysis was performed and equilibrium structures, sets of fundamental vibrations, moments of inertia, and total energies of the stablest conformers of I, II, and III were calculated by the B3LYP/6-311G(d,p), G3MP2, and CBS-QB3 methods. The experimental IR spectra and calculated vibrational frequencies were used to obtain sets of fundamental vibrations of the stablest conformations. The thermodynamic properties of I–III in the ideal gas state were determined over the temperature range 0–1500 K. Additive and quantum-chemical methods were applied to estimate the Δf H o(g) values of a number of γ-lactones. Composite quantum-chemical methods were used to obtain the energies of monomethyl γ-butyrolactones and estimate their relative stability depending on the position of the methyl substituent in the ring. 相似文献
2.
M. R. Bissengaliyeva D. B. Gogol’ N. S. Bekturganov 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2011,85(2):157-163
The heat capacity of natural mineral, pyromorphite Pb5(PO4)3Cl, was measured over the temperature range 4.2–320 K using low-temperature adiabatic calorimetry. An anomalous temperature
dependence of heat capacity with a maximum at 273.24 K was observed between 250 and 290 K. The heat capacity, entropy, enthalpy,
and reduced thermodynamic potential of pyromorphite were calculated and tabulated over the temperature range 5–320 K. The
standard thermodynamic functions of the mineral are C
p298.15o = 414.98 ± 0.44 J/(mol K), S
298.15o = 585.31 ± 0.99 J/(mol K), H
298.15o − H
0o = 80.90 ± 0.08 kJ/mol, and Φ298.15o = 313.97 ± 0.84 J/(mol K). 相似文献
3.
Possible geometrical structures and relative stabilities of (F2AlN3)
n
(n = 1–4) clusters were studied using density functional theory at the B3LYP/6-311+G* level. The optimized clusters (F2AlN3)
n
(n = 2–4) possess cyclic structure containing Al–Nα–Al linkages, and azido in azides has linear structure. The IR spectra of the optimized (F2AlN3)
n
(n = 1–4) clusters have three vibrational sections, the whole strongest vibrational peaks lie in 2218–2246 cm−1, and the vibrational modes are N3 asymmetric stretching vibrations. Trends in thermodynamic properties with temperature and oligomerization degree n are discussed, respectively. A study of their thermodynamic properties suggests that monomer 1A forms the most stable clusters
(2A, 3A, and 4B) can occur spontaneously in the gas phase at temperatures up to 800 K. 相似文献
4.
Pu Su Zhao Ji Ming Xu Wei Guang Zhang Fang Fang Jian Lan Zhang 《Structural chemistry》2007,18(6):993-1000
The title compound of 3-p-methylphenyl-4-amino-1, 2, 4-triazole-5-thione was synthesized and characterized by elemental analysis, IR, electronic spectra,
and X-ray single crystal diffraction. Quantum chemical calculations of the structure, natural bond orbital, and thermodynamic
functions of the title compound were performed by using B3LYP/6-311G** and HF-6-311G** methods. Both the methods can well
simulate the molecular structure. Vibrational frequencies were predicted, assigned and compared with the experimental values,
and B3LYP/6-311G** method is superior to HF/6-311G** method to predict the vibrational frequencies. Electronic absorption
spectra calculated by B3LYP/6-311G** method have some red shifts compared with the experimental ones and natural bond orbitals
analyses indicate that the two absorption bands are mainly derived from the contribution of n → π* and π → π* transitions. On the basis of vibrational analyses, the thermodynamic properties of the title compound at different temperatures
have been calculated, revealing the correlations between C
0
p,m
, S
0
m
, H
0
m
, and temperatures. 相似文献
5.
T. A. Bykova N. N. Smirnova T. G. Kulagina L. V. Nikishchenkova G. P. Belov E. V. Novikova 《Russian Chemical Bulletin》2005,54(6):1527-1531
The temperature dependence of the heat capacity of an alternating copolymer of bicyclo[2.2.1]hepta-2,5-diene and carbon monoxide
in the temperature range 6–550 K (with an error of 0.2–0.5% at 6–350 K and 0.5–1.5% at 330–550 K) was studied by the adiabatic
vacuum and dynamic calorimetry. Physical transformations of the copolymer in the studied temperature region were identified,
and their thermodynamic characteristics were determined. The combustion energy of the copolymer at 298.15 K was measured in
a calorimeter with a static bomb and isothermal jacket. The thermodynamic functions for a region of 0–550 K, enthalpy of combustion,
and thermodynamic parameters of copolymer formation from simple substances at T = 298.15 K and p = 101.325 kPa were calculated from the obtained experimental data. The new results and earlier published data were used for
the calculation of the thermodynamic characteristics of the alternate copolymerization of bicyclo[2.2.1]hepta-2,5-diene and
CO under standard pressure for a region of 0–350 K for the bulk reaction.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1483–1487, June, 2005. 相似文献
6.
B. V. Lebedev K. B. Zhogova Ya. V. Denisova G. P. Belov O. N. Golodkov 《Russian Chemical Bulletin》1998,47(2):277-281
The temperature dependence of the heat capacity of the alternating copolymer (ACP) of carbon monoxide with ethylene was studied,
and temperatures and enthalpies of its phase transformations were measured by adiabatic vacuum, dynamic, and isothermal calorimetry
in the temperature range from 8 to 600 K. The energy of burning of ACP was measured at 298.15 K in a calorimeter with the
static bomb and isothermal shell. The thermodynamic parameters of transformation of the α-form of ACP crystals into the β-form
and fusion of the β-form were determined. The thermodynamic functions for the 0–507 K range and thermodynamic characteristics
atT=298.15 K andp=101.325 kPa were calculated. The thermodynamic parameters of the alternating copolymerization of ethylene and CO at 0–507
K and standard pressure were calculated for the bulk reaction.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 284–288, February, 1998. 相似文献
7.
The relative thermodynamic stabilities of 2,5-dihydrofuran (1) and 2,3-dihydrofuran (2), and of 3,4-dihydro-6H-pyran (3) and 3,4-dihydro-2H-pyran (4), were determined at several temperatures by base-catalyzed equilibration in DMSO solution. For 1 → 2, = –15.4±0.1 kJ mol−1, =–12.6±0.5 kJ mol−1, and =9.5±1.3 J K−1 mol−1 at 298.15 K. The second-law reaction enthalpy agrees with literature data based on calorimetric enthalpies of hydrogenation of the isomeric forms in hexane. For 3 → 4, =–19.3±0.2 kJ mol−1, = –18.9±1.1 kJ mol−1 and =1.1±3.0 J K−1 mol−1 at 298.15 K: the experimental reaction enthalpy is in marked disagreement with literature data based on estimation. On the other hand, both of the experimental reaction enthalpies of the present study are in good agreement with DFT calculations using the B3LYP functional and 6-311+G(2d,p) basis set. 相似文献
8.
N. N. Smirnova A. V. Markin Ya. S. Samosudova G. M. Ignat’eva A. M. Muzafarov 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2010,84(5):784-791
The temperature dependence of the heat capacity of carbosilane dendrimer of the seventh generation of series 3 × 3 with phenylic
substituent on the initial branching center and terminal butyl groups was studied by the methods of precision adiabatic vacuum
calorimetry and differential scanning calorimetry over the temperature range T = 7–580 K for the first time. Physical transformations in the above temperature range were detected and their standard thermodynamic
characteristics estimated and analyzed. The experimental results were used to calculate standard thermodynamic functions C
p
∘(T), H
∘(T)-H
∘(0), S
∘(T)-S
∘(0), and G
∘(T)-H
∘(0) (0) over the range T → 0–580 K and standard entropy of formation of dendrimer at T = 298.15 K. The thermodynamic properties of carbosilane dendrimers of the seventh generation of series 4 × 3 with terminal
butyl groups and the samples studied in this work were compared. 相似文献
9.
The Becke3LYP functional of DFT theory was used to investigate molecular structure and sodium affinity of the systems CH3CO2Na (1), CH3–O–SO3Na (2), CH3–NH–SO3Na (3), saccharide_1Na2 (4), saccharide_2Na (5), saccharide_3Na3 (6), saccharide_4Na2 (7), and saccharide_5Na2 (8), respectively, which are models of N- and O-sulfate glycosaminoglycans. Interaction enthalpies, entropies and Gibbs energies of the sodium-coordinated systems in the
gas phase were determined with the B3LYP/6-311+G(d,p) and B3LYP/6-31+G(d) methods. The computed Gibbs energies, ΔG
o
, of model systems 1–3 are negative and span a rather broad energy interval (from −500 to −1,500 kJ mol−1). Gibbs interaction energies for sodium acetate, sodium sulfate and sodium sulfamate functions of the five saccharides, systems
4–8 are always lower than those values found for the model compounds 1–3. The ionization of sodium salts of saccharides studied in gas phase is in most cases connected with considerable conformational
rearrangement of the ionic species. This rearrangement causes an additional energetic stabilization of anionic species and
is connected with the substantial release of entropy. 相似文献
10.
Hassan M. Badawi Shaikh A. Ali 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2009,74(2):558-562
The conformational stability and the C–O and O–H internal rotations in oxiranemethanol were investigated at the DFT-B3LYP/6-311G**, MP2/6-311G** and MP4(SDQ)/6-311G** levels of theory. Three minima were predicted in the CCOH potential energy scans of the molecule to have relative energies of about 2 kcal/mol or less and all were calculated to have real frequencies upon full optimization of structural parameters at the DFT and the MP2 levels of calculations. The Cg1 (H bond inner) conformation was predicted to be the lowest energy conformation for oxiranemethanol in excellent agreement with an earlier microwave study. The equilibrium mixture was calculated from Gibb's free-energy changes to be about 79% Cg1, 17% G1g and 3% Gg1 at the B3LYP/6-311G** level and about 87% Cg1, 11% G1g and 2% Gg1 at the MP2/6-311G** level for oxiranemethanol at 298.15 K. No conclusive evidence was obtained for the presence of high-energy form in the liquid phase of oxiranemethanol. The vibrational frequencies of oxiranemethanol in its three stable forms were computed at the B3LYP level and complete vibrational assignments were made for the lowest energy Cg1 form on basis of calculated and experimental data of the molecule. 相似文献
11.
A. N. Egorova M. V. Vener I. S. Zhukov G. D. Kozak V. G. Tsirelson 《Russian Chemical Bulletin》2008,57(6):1179-1186
Conformational analysis of cumene hydroperoxide PhCMe2OOH (1) has been carried out using the density functional methods B3LYP/6-31G(d,p) and B3LYP/6-311+G(3df,2p). Ignoring rotation
of methyl groups, molecule 1 has seven conformers differing in orientation of the — CMe2OOH fragment relative to the benzene ring and in mutual position of atoms in this fragment. The molecular structures, relative
energies, and statistical distribution of the conformers were determined, and intramolecular rotational barriers were estimated.
The enthalpies of formation of all conformers of molecule 1 were calculated using two approximations with inclusion of zero-point vibrational energy and temperature correction. Calculations
using the isodesmic reaction (IDR) scheme made it possible to reduce the systematic error of the determination of the enthalpy
of reactions. The total enthalpy of formation of compound 1 calculated with inclusion of statistical distribution of rotamers equals −19.7±3.6 kcal mol−1. The combination of the B3LYP/6-31G(d,p) approximation and the IDR scheme gives fairly accurate results (relative error is
±0.4 kcal mol−1) as compared to those obtained with the extended basis set 6-311+G(3df,2p).
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1157–1164, June, 2008. 相似文献
12.
M.-H. Wang Z.-C. Tan Q. Shi L.-X. Sun T. Zhang 《Journal of Thermal Analysis and Calorimetry》2006,84(2):413-418
The
heat capacities of 2-benzoylpyridine were measured with an automated adiabatic
calorimeter over the temperature range from 80 to 340 K. The melting point,
molar enthalpy, ΔfusHm,
and entropy, ΔfusSm,
of fusion of this compound were determined to be 316.49±0.04 K, 20.91±0.03
kJ mol–1 and 66.07±0.05 J mol–1
K–1, respectively. The purity of the compound
was calculated to be 99.60 mol% by using the fractional melting technique.
The thermodynamic functions (HT–H298.15) and (ST–S298.15) were calculated based
on the heat capacity measurements in the temperature range of 80–340
K with an interval of 5 K. The thermal properties of the compound were further
investigated by differential scanning calorimetry (DSC). From the DSC curve,
the temperature corresponding to the maximum evaporation rate, the molar enthalpy
and entropy of evaporation were determined to be 556.3±0.1 K, 51.3±0.2
kJ mol–1 and 92.2±0.4 J K–1
mol–1, respectively, under the experimental
conditions. 相似文献
13.
N. N. Smirnova K. V. Kandeev T. A. Bykova T. G. Kulagina A. M. Fainleib 《Russian Chemical Bulletin》2006,55(5):845-851
The temperature dependences of the heat capacity of partially crystalline linear polyurethanes based on 1,6-hexamethylenediisocyanate
with butane-1,4-diol and hexane-1,6-diol were studied for the first time in a temperature range of 6–460 K by the methods
of adiabatic vacuum and dynamic calorimetry. Physical changes in the state of polyurethanes were revealed and characterized;
the standard thermodynamic functions, namely, C
p
°(T), H°(T)-H°(0), S°(T), and G°(T)-H°(0), were calculated from the obtained experimental data in the temperature range from T → 0 to 460 K for the polymers in the crystalline, glassy, highly elastic, and liquid states. The energies of combustion of
the polymers were measured by the bomb calorimetry method, and the standard thermodynamic characteristics of their formation
at 298.15 K were calculated. The thermodynamic characteristics of bulk polycondensation of 1,6-hexamethylenediisocyanate with
butane-1,4-diol and hexane-1,6-diol to form linear aliphatic polyurethanes-{4,6} and-{6,6} were determined in the range from
T → 0 to 350 K at p° = 0.1 MPa. The thermodynamic properties of the polyurethanes under study and polymers of isomeric structure were compared.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 817–823, May, 2006. 相似文献
14.
Qing-Fen Meng Zhi-Cheng Tan Ya-Ping Dong Hai-Tao Feng Xiao-Huan Wang Quan Shi Wu Li 《Journal of solution chemistry》2010,39(7):1087-1098
The molar heat capacities of three different concentrations of aqueous SrCl2 solutions, 0.1212, 0.4615 and 1.878 mol⋅kg−1, were measured, using a precision automated adiabatic calorimeter in the temperature range from 80 to 320 K. Solid–liquid
phase transitions were observed at 272.83, 270.18 and 255.15 K, respectively, for these three solutions. The molar enthalpies
and entropies of the phase transitions were evaluated. The experimental heat capacity data were fitted to polynomial equations,
and based on the polynomial equations and thermodynamic relationship, the thermodynamic functions relative to 298.15 K, [H
T
−H
298.15 K] and [S
T
−S
298.15 K], of the three solutions were derived in the range of 80 to 320 K with an interval of 5 K. 相似文献
15.
E. G. Baskir I. P. Klimenko Yu. V. Tomilov O. M. Nefedov 《Russian Chemical Bulletin》2005,54(5):1100-1104
The electronic structures and dissociation energies of diazocyclopropane (1), diazomethane (2), 2-diazopropane (3), and diazocyclobutane (4) were calculated at the density functional B3LYP and the ab initio MP2 levels using the 6-31G(d) basis set and at the G2(MP2,SVP)//B3LYP/6-31G(d) level. Distinctive features of diazocyclopropane
1 are the low energy of dissociation with loss of the nitrogen molecule; ΔE = 18.7 kcal mol−1, B3LYP; 9.2 kcal mol−1, G2 at 0 K) and a nonplanar structure, in which the C=N bond forms an angle of 115.7° with the plane of the cyclopropane
ring. The behavior of molecules 1 and 2 in the 1,3-dipolar cycloaddition to ethylene (5), acrylonitrile (6), and methyl acrylate (7) was studied. The reactions of 1 with 6 and 7 have very low activation barriers (ΔE
a = 4.7 and 4.4 kcal mol−1, respectively; at the B3LYP level). For these reactions, the G2 method gives even smaller activation parameters (1.8 and
0.3 kcal mol−1, respectively). The results of our calculations provide a good explanation for high reactivity of diazocyclopropane 1.
Dedicated to Academician N. K. Kochetkov on the occasion of his 90th birthday.
__________
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1072–1076, May, 2005. 相似文献
16.
A. N. Chekhlov 《Russian Journal of Inorganic Chemistry》2008,53(9):1465-1469
Three new crystalline complexes are synthesized: [K(18-crown-6)]+ · An, where An = [FeCl4]?(I), [FeBr2Cl2]? (II), and [FeBr4]? (III). The crystals of compounds I–III are cubic and isomorphic, space group Fd $ \bar 3 Three new crystalline complexes are synthesized: [K(18-crown-6)]+ · An, where An = [FeCl4]−(I), [FeBr2Cl2]− (II), and [FeBr4]− (III). The crystals of compounds I–III are cubic and isomorphic, space group Fd
(Z = 16): a = 20.770(2) ? for I, 20.844(3) ? for II, and 20.878(4) ? for III. Structures I–III are solved by a direct method and refined by the full-matrix least-squares method in the anisotropic approximation to R = 0.047 (I), 0.059 (II), and 0.098 (III) for all 680 (I), 684 (II), and 686 (III) independent reflections. In two tetrahedral anions [Fe(1)X4]− and [Fe(2)X4]− in structures I–III, all halogen atoms (X = Cl and Br) are randomly disordered over three close positions relative to the crystallographic axes
3. Structures I–III contain the [K(18-crown-6)]+ host-quest complex cation. The K+ cation (CN = 8) resides in the cavity of the 18-crown-6 ligand and coordinated by its six O atoms and two disordered halogen
X atoms. The coordination polyhedron of the K+ cation in complexes I–III is a distorted hexagonal bipyramid.
Original Russian Text ? A.N. Chekhlov, 2008, published in Zhurnal Neorganicheskoi Khimii, 2008, Vol. 53, No. 9, pp. 1566–1570. 相似文献
17.
The heat capacities of N-(tert-butoxycarbonyl)-l-phenylalanine (abbreviated to NTBLP in this article), as an important chemical intermediates used to synthesize proteins
and polypeptides, were measured by means of a fully automated adiabatic calorimeter over the temperature range from 78 to
350 K. The measured experimental heat capacities were fitted to a polynomial equation as a function of temperature. The thermodynamic
functions, H
T − H
298.15K and S
T − S
298.15K, were calculated based on the heat capacity polynomial equation in the temperature range of (80–350 K) with an interval of
5 K. The thermal stability of the compound was further studied using TG and DSC analyses; a possible mechanism for thermal
decomposition of the compound was suggested. 相似文献
18.
D. Sedmidubský J. Leitner P. Svoboda Z. Sofer J. Macháček 《Journal of Thermal Analysis and Calorimetry》2009,97(2):403-407
The low temperature heat capacities of three A
IIInitrides, A
III=Al, Ga and In, were measured by relaxation method in the temperature range 2–300 K and the corresponding entropies at the
reference temperature 298.15 K were evaluated from the experimental data. The lattice heat capacity at constant volume was
also assessed theoretically within harmonic crystal approximation by direct method using a combination of VASP software package
to obtain the Hellmann-Feynman forces and the Phonon program to calculate the phonon spectra. The experimental data were analyzed
by means of a Debye-Einstein model taking use of the calculated heat capacity and involving additionally an anharmonic contribution. 相似文献
19.
Two-dimensional cyclic potential energy surface for internal rotation of vinyl and hydroxyl substituents in o-vinylphenol molecule was constructed by the B3LYP/6-311G(d) method. It was shown that o-vinylphenol molecule exists in the gas phase as a mixture of seven rotamers denoted as A (A′), B (B′), C (C′) and D. The B3LYP/cc-pVTZ calculated percentage of the rotamers A and A′ in which OH…π intramolecular interaction occurs, is at most 24%. The height of barriers t interconversions between o-vinylphenol rotamers varies from 0.1 to 5.2 kcal mol−1. According to B3LYP/cc-pVTZ calculations, the inclusion of solvent effect in the framework of the polarizable continuum model
for a solution of o-vinylphenol in CCl4 leads to a decrease in theoretical values of ν(OH) frequencies by about 4–9 cm−1 and to an increase in the percentage of the rotamers without intramolecular hydrogen bond by about 4.3% compared to the corresponding
gas-phase values. The simulated IR spectral contours of ν(OH) bands are in good agreement with experimental one
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 499–508, March, 2008. 相似文献
20.
A. N. Veselkov L. N. Djimant V. I. Pakhomov S. G. Osetrov A. Tucker D. B. Davies 《Journal of Structural Chemistry》1999,40(2):220-229
Complexation of a phenanthridine dye ethidium bromide with a desoxyoligonucleotide 5’-d(GpApCpAp-TpGpTpC) in aqueous salt
solution is studied by one- and two-dimensional1H NMR spectroscopy. Two-dimensional correlated homonuclear PMR spectroscopy (2D-TOCSY and 2D-N0ESY) was used for complete
assignment of the proton signals of molecules in solution and for qualitative analysis of the character of interaction between
ethidium bromide and desoxyoctanucleotide. The concentration dependences of the proton chemical shifts of the molecules were
measured at three temperatures (T1 = 298 K, T2 = 308 K, and T3 = 318 K); the temperature dependences were measured in the temperature range 278–358 K. Different schemes of dye complexation
with an octamer duplex involving different molecular associates in solution are considered. The equilibrium constants of the
reactions, the corresponding thermodynamic parameters (δH0, δS0), and the limiting values of the chemical shifts of ethidium bromide protons in the complexes are determined. The relative
contents of complexes of different types in solution (dye complexes with desoxyoctanucleotide in duplex form) are analyzed,
and peculiarities of the dynamic equilibrium depending on the ratio of dye and octamer concentrations and temperature are
established. The most probable structures of the 1:2 and 2:2 intercalated complexes corresponding to dye intercalation into
the pyrimidine-purine sites of the desoxyoctanucleotide duplex are derived using the calculated values of the induced proton
chemical shifts of ethidium bromide and two-dimensional PMR data.
Translated fromZhurnal Strukturnoi Khimii, Vol.40, No. 2, pp. 265–275, March–April, 1999. 相似文献