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1.
After the separation of the donor, the acceptor, and the σ-type bridge from the π-σ-π system, the geometries of biphenyl,
biphenyl anion radical, naphthalene, and naphthalene anion radical are optimized, and then the reorganization energy for the
intermolecular electron transfer (ET) at the levels of HF/4-31G and HF/DZP is calculated. The ET matrix elements of the self-exchange
reactions of theπ-σ-π systems have been calculated by means of both the direct calculation based on the variational principle,
and the transition energy between the molecular orbitals at the linear coordinateR = 0.5. For the cross reactions, the ET matrix element and the geometry of the transition state are determined by searching the minimum
energy splitting Δmin along the reaction coordinate. In the evaluation of the solvent reorganization energy of the ET in solution, the Marcus’
two- sphere model has been invoked. A few of ET rate constants for the intramolecular ET reactions for the π-σ-π systems,
which contain the biphenylyl as the donor and both biphenylyl and naphthyl as the acceptor, have been obtained.
Project supported by the National Natural Science Foundation of China (Grant Nos. 29706104 and 29573112), the State Key Laboratory
of Theoretical and Computational Chemistry of Jilin University. 相似文献
2.
The conformational stabilities of the α- and β-substituted enamines and vinyl ethers were predicted by orbital phase theory
and confirmed by ab initio molecular orbital calculations. Cyclic interaction significantly occurs among the nonbonding orbital
n
Y for the lone pair on the hetero atom Y (N in the enamines or O in the ethers), the π and π* orbitals of the CC bond, and the
σC-H or σ*C-X orbitals on the substituent CH2X. The cyclic -n
Y-π-σC-H-π*- interaction is favored by the orbital phase continuity in the α-substituted molecules, while the cyclic -n
Y-π-σ*C-X-π*- interaction is favored in the β-substituted molecules. The most stable conformation was then predicted to be synperiplanar
or (pseudo)equatorial in the α-substituted molecules and anticlinical or (pseudo)axial in the β-substituted molecules.
Received: 8 May 1998 / Accepted: 30 July 1998 / Published online: 16 November 1998 相似文献
3.
The CEPA-PNO method is used for calculating the energy difference ΔE
ST between the3∑− and the1Δ states of diatomic molecules in electronic π2 configurations. An analysis of the contribution of electron correlation to ΔE
ST is performed in terms of physically understandable effects such as direct correlation, dynamic spin polarization, semiinternal
and internal excitations. It is shown that these effects are of completely different importance for the molecules treated
in this study: For C2 the direct correlation between the two singly occupied π-orbitals is the dominant correlation contribution to ΔE
ST; for O2, S2, SO the internal excitation π
u
2
→ π
g
2
is predominant, whereas for NH and PH there is a close competition between the direct correlation and the spin polarization
of the underlying σ-orbitals. The basis set dependence of these effects is investigated, in particular for NH. Our final results
reproduce experimental values of ΔE
ST within 0.05–0.10 eV. 相似文献
4.
B. V. Ni 《Journal of Structural Chemistry》1995,36(2):259-264
This paper studies changes in the matrix elements (Ump) of spin-orbit coupling between the nπ*- and ππ*-states, which are induced by the (“chair,” “bath”) distortions of the nuclear configurations of molecules. The analysis is
performed for acridine molecules in which the n-pz atomic orbital (AO) of the heteroatom is directed along the C2 symmetry axis. Earlier, for molecules with a planar nuclear configuration of C2v symmetry and with the heteroatom lying on the C2 axis, we established the dependence of Ump on the symmetry of ππ*-states [Γ(ππ*)=A1 or B2]. The values of Ump differ by more than one order of magnitude; this is in line with the difference between the interconversion rate constants
(Kisc; two or three orders). In this work we have found that this contrast in Ump (and, accordingly, in Kisc) is retained when the nuclear configuration of the acridine molecule is distorted to the “chair” (AC-A) configuration, although
the individuality of both molecular orbital types (nσ-MO and π-MO) and states nπ* and ππ* is annihilated to a certain extent. For the “bath” (AC-B) conformation the difference in Ump considerably diminishes. Reasons for the changes in the matrix elements of spin-orbit coupling and rate constants of the
S-T conversion are analyzed. The available energy level diagram is critically analyzed, and a slightly different diagam as
well as a scheme of nonradiating deactivation of acridine are suggested.
L. Ya. Karpov Physicochemical Scientific Research Institute. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 2, pp. 292–297, March–April, 1995.
Translated by L. Smolina 相似文献
5.
Sequential Monte Carlo/quantum mechanical calculations are performed to study the solvent effects on the electronic absorption
spectrum of formamide (FMA) in aqueous solution, varying from hydrogen bonds to the outer solvation shells. Full quantum-mechanical
intermediate neglect of differential overlap/singly excited configuration interaction calculations are performed in the supermolecular
structures generated by the Monte Carlo simulation. The largest calculation involves the ensemble average of 75 statistically
uncorrelated quantum mechanical results obtained with the FMA solute surrounded by 150 water solvent molecules. We find that
the n → π* transition suffers a blueshift of 1,600 cm−1 upon solvation and the π → π* transition undergoes a redshift of 800 cm−1. On average, 1.5 hydrogen bonds are formed between FMA and water and these contribute with about 20% and about 30% of the
total solvation shifts of the n → π* and π → π* transitions, respectively. The autocorrelation function of the energy is used
to sample configurations from the Monte Carlo simulation, and the solvation shifts are shown to be converged values.
Received: 14 March 2002 / Accepted: 3 April 2002 / Published online: 24 June 2002 相似文献
6.
Qiang Wei Ying Ke Xie Feng Zhang 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2011,85(8):1376-1379
The stereodynamics of the O + HCl → ClO + H reaction are investigated by quasi-classical trajectory (QCT) method. The calculations
are carried out on the ground 1 1
A′ potential energy surface (PES). The orientation and alignments of the product rotational angular momentum for the title
reaction are reported. The influence of collision energy on the product vector properties is also studied in the present work.
Four (2π/σ)(dσ00/dω
t
), (2π/σ)(dσ20/dω
t
), (2π/σ)(dσ22+/dω
t
), and (2π / σ)(dσ21−/dω
t
), and have been calculated in the center of mass frame. 相似文献
7.
V. A. Nikanorov O. L. Tok S. G. Novikov S. V. Sergeev E. V. Vorontsov I. D. Gridnev D. V. Zverev A. T. Lebedev 《Russian Chemical Bulletin》1997,46(2):350-354
Three approaches to the synthesis ofN-substituted imino-, hydrazono-, and azino-2,5-cyclohexadienylidene systems based on reactions of 4-methyl-4-trichloromethylcyclohexa-2,5-dienone
with aminophenols and hydrazones and condensation of hydrazones ofpara-semiquinoid ketones with carbonyl compounds, including that of the ferrocene series, were realized. The latter reaction,
when applied to 3,6-dibromophenanthrene-9, 10-quinone, was accompanied by quantitative aromatizational molecular rearrangement
with the elimination of the CCl3 group. Using Rh1 complexes as an example, it was shown that the heteroorganic ligands obtained can be used for the synthesis of mixed-ligand
metallocomplexes with triple coordination of the metal atom including simultaneous metal-ligand interactions of the n-, π-,
and σ-types.
The principle of metal-ligand “cascade” appeared as a result of the generalization of two new phenomena of organometallic
sereodynamics, which we have found recently2,3 and have called oxidative and reductive redox-rotation. In the “cascade”, type1 (“metal-ligand-metal”) or type2 (“ligand-metal-ligand”) metallocomplexes, one or several coordinated metal ligand”) metallocomplexes, one or several coordinated
metal atoms capable of concertedly and reversibly changing their valence in the course of intramolecular conformational transformation
are in positions of mutual conjugation.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 363–367, February, 1997. 相似文献
8.
The ability of cyclopentadienyl type derivatives of corannulene C20H10 and fullereneI
h
-C60 to form η5-π-complexes and the problem of their existence is discussed. MNDO/PM3 calculations of half-sandwich complexes η5-π-MC20H15, η5-π-MC20H
15
+
, η5-π-MC60H5, η5-π-MC60H5 and sandwich complexes 2η5-π-M(C20H15)2, 2η5-π-M(C20H15)2, 2η5-π-M(C60H5)2 (M=Si, Ge, Sn, Pb) were performed. For all systems studied, local minima were found on corresponding potential energy surfaces
and the heats of formation, geometric parameters, and distributions of effective atomic charges were calculated. Sandwich
complexes are most likely to exist with M=Si and Ge. The energy and geometric characteristics of η5-π-complexes of corannulene were compared with those of η5-π-complexes of fullereneI
h
-C60. It was concluded that the results of quantum-chemical calculations of sandwich type corannulene derivatives can be used
for simulation of the geometry and electronic structure of analogous complexes of fullereneI
h
-C60.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1649–1656, September, 1999. 相似文献
9.
The “analytical power” of detection systems is investigated, considering typical arrangements in analytical terms. From N
atoms of interest in a sample Z counts are drawn: Z=R N (R registration yield). Crude data ZM contain also background U generated
by interferences: ZM=Z+U. Identification and separation of Z is accompanied by errors ~σMU1/2 due to imperfect distinguishability and to statistical error (σM model inherent factor). With “selectivity”=σM
- (R/Rinterference)1/2 the figure of merit is G=selectivity efficiency/interference)1/2. Sample background dominating, “interference” or both “interference” and “efficiency” have to be cancelled. Present semiconductor
spectrometry of low energy γ-quanta and of large rates is not very far from its limits. Further progress will be obtained
by enhancement of high energy efficiency and reduction of natural background.
相似文献
10.
Theoretical calculations have been used to examine singlet oxygen release from a naphthalene endoperoxide which bears a flexible
(CH2)22 polymethylene “lid”. Monte Carlo and ONIOM calculations that incorporated semi-empirical and density functional theory predicted
the conformational influence of the polymethylene chain in the cycloreversion of dioxapaddlane, 1,4-diicosa naphthalene-1,4-endoperoxide,
to 1O2 and 1,4-diicosa naphthalene. This study attempts to build a connection between 1O2 generation and “jump rope” dynamics of the dioxapaddlane. The polymethylene chain appears to function as a gatekeeper for
the oxygen. Instead of coming full circle, a semi-circle rotation of the polymethylene bridge protected the peroxide group,
limiting the dissociation of 1O2 from the naphthalene site.
Dedicated to István Hargittai for his first twenty years at Structural Chemistry. 相似文献
11.
12.
The chiroptical properties associated with then-π* (singlet-singlet) transitions in dissymmetric barbituric acid derivatives are examined on the basis of two theoretical models.
The lower singlet excited states of unsubstituted and alkyl substituted barbituric acids are calculated on the semi-empirical
CNDO/S-CI molecular orbital model, and the spectroscopic properties associated with transitions to these states are computed.
In the structures we examined, threen-π* transitions are found at λ>220 nm, two of which are nearly degenerate. Each of these transitions is computed to be strongly
magnetic dipole allowed and to be forbidden or very weak (depending upon the exact symmetry and geometry of the trioxopyrimidine
moiety) in electric dipole radiation. Contributions from chiral distortions within the trioxopyrimidine chromophoric system
to the rotatory strengths of the three lowest energyn-π* transitions are calculated directly from wave functions obtained by the CNDO/S-CI method. Contributions to then-π* rotatory strengths arising from “vicinal” interactions between the trioxopyrimidine chromophore and asymmetric substituent
groups are calculated by a perturbation method based on an independent systems representation of the optically active compounds.
Various spectra-structure relationships are considered and correlations between experimental data and theoretically calculated
results are examined. 相似文献
13.
Within the general context of homometallic spin-coupled Cu(II) dimers, we propose to relate the antiferromagnetic part of
the exchange coupling constant, J
AF, to the quantity ΔP
2(Cu), the difference of copper squared spin populations as calculated for the high-spin (i.e. triplet) and broken-symmetry
spin states, through J
AF≈−UΔP
2(Cu), where U is interpreted as the covalent–ionic term. This proportionality is illustrated for three “bare” Cu(II) dimers (i.e. without
peripheral ligation, so as to enhance the antiferromagnetic contribution) bridged by azido, hydroxo, or oxo groups. This provides
an alternative quantifier of the exchange phenomenon to that usually used, i.e. Δ2, the square of the singly occupied molecular orbital splitting in the triplet state. Moreover, and quite interestingly, the
quantity ΔP
2(Cu) can become negative (i.e. induce ferromagnetism) without apparently affecting the proportionality relation.
Received: 17 September 1999 / Accepted: 9 March 2000 / Published online: 21 June 2000 相似文献
14.
Transition states for the insertion reactions of singlet mono and dichlorocarbenes (1CHCl and 1CCl2) into C-H bonds of alkanes (methane, ethane, propane and n-butane) have been investigated at MP2 and DFT levels with 6–31g (d, p) basis set. The p
π
of 1CHCl and 1CCl2 may interact with alkane’s filled fragment orbital of either σ or π symmetry. So chlorocarbenes insertion reactions have been investigated for both (σ/π) approaches. The σ approach has been adjudicated to be the minimum energy path over the π approach both at the MP2 and DFT levels. Mulliken, NPA and ESP derived charge analyses have been carried out along the minimal
energy reaction path using the IRC method for 1CHCl and 1CCl2 insertions into the primary and secondary C-H bonds of propane. The occurrence of TSs either in the electrophilic or nucleophilic
phase has been identified through NBO charge analyses in addition to the net charge flow from alkane to the carbene moiety.
Dedicated to our senior colleague Dr V Sethuraman on the occasion of his retirement from collegiate service 相似文献
15.
This paper deals with the mechanisms of localization of Franck-Condon vibronic coupling of πσ*- or πlπ*-orbital type in a few vibrational modes, (LVM) in excited electronic states of polyatomic molecules. The analysis of vibronic
coupling uses highly symmetric basis sets (for representing MO structures and normal coordinates ξR) as well as simplified models that relate the shift ΔR of the electron potential minima along the normal coordinates to the MO structure and to ξR in the form of analytical expressions. The modes that are active in LVM are determined from the experimental luminescence
spectra. These ideas about approximately high local symmetry of vibronic coupling in benzene fragments as well as the estimates
of ΔR depending on variations in the MO structure explain the experimental results.
L. Ya. Karpov Physicochemical Scientific Research Institute. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 2, pp. 286–291, March–April, 1995.
Translated by L. Smolina 相似文献
16.
Studying the kinetics of PtCl4
2-
cis-[Pt(NH3)2(H2O)2]2+ and cis-Pt(NH3)2Cl2 (cis-DDP) reactions with different types of ligands using spectrophotometric, Potentiometric and EPR methods, the conditions for
Pt(III) formation as transient species and its further stabilization as “Platinum Blue” complexes were found. A general method
for obtaining “Platinum Blue” species is suggested. 相似文献
17.
Chun-lan Yuan 《Kinetics and Catalysis》2011,52(5):697-701
A closed oscillation system comprised of alanine, KBrO3, H2SO4 and acetone catalyzed by tetraazamacrocyclic nickel(II) complex is introduced, and quantitatively characterized with kinetic
parameters, namely the rate constant (k
in, k
p), the apparent activation energy (E
in, E
p) and pre-exponential constant (A
in, A
p) and thermodynamic functions (ΔH
in, ΔG
in, ΔS
in and ΔH
p, ΔG
p, ΔS
p), where indexes “in” and “p” mean “induction period” and “oscillation period,” respectively. The results indicate that tetraazamacrocyclic
nickel(II) complex can catalyze alanine oscillating reaction and the reaction corresponds exactly to the feature of irreversible
thermodynamics as the entropy of system is negative. 相似文献
18.
Joint results of the differential scanning calorimetry (DSC) and thermogravimetry (TG) experiments were the basis for the
fusion enthalpy and temperature determination of the biuret (NH2CO)2NH (synthesis by-product of the urea fertilizer (NH2)2CO). Recommended values are Δm
H = (26.1 ± 0.5) kJ mol−1, T
m = (473.8 ± 0.4) K. The DSC method allowed for the phase diagrams of “water–biuret,” “water–urea,” “urea–biuret” binary systems
to be studied; as a result, liquidus and solidus curves were precisely defined. Stoichiometry and decomposition temperature
of the biuret hydrate identified, composition of the compound in “urea–biuret” system was suggested. 相似文献
19.
A. N. Egorochkin S. E. Skobeleva T. G. Mushtina E. T. Bogoradovsky 《Russian Chemical Bulletin》1998,47(8):1526-1531
The integrated extinction coefficients (A) of the C≡C stretching modes in the IR spectra of 12 germylacetylenes Me3GeC≡CR are determined by the resonance interactions of substituents with the triple bond. TheA
1/2 values change linearly with change in the difference between the effective π-electron charges on the atoms at the triple
bond and σ0
R constants of organic substituents R. The average value of the σ0
R constant of the Me3Ge substituent in the compounds studied is +0.06. The resonance acceptor effect of the Me3Ge substituent toward the triple bond (d,π-conjugation) is stronger than the donor effect (σ,π-conjugation).
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1569–1574, August, 1998. 相似文献
20.
The enthalpies of dissolution of glycine (Gly) and L-α-alanine (Ala) in water at 288.15–318.15 K were measured. The results were compared with the earlier obtained data for L-α-phenylalanine (Phe) and L-α-histidine (His). The standard enthalpies of dissolution (Δsoln
H
0) and differences (ΔC
p
0
) between the limiting partial molar heat capacity of the amino acids in solution and the heat capacity of the amino acids
in the crystalline state
were calculated in the temperature interval 273–373 K. Changes in the entropy of dissolution (ΔΔsoln
S
0) and reduced Gibbs energy [Δ (Δsoln
G
0/T)] in the temperature interval from 273 to 373 K were determined from the known thermodynamic relationships. The ΔC
p
0
value is negative for hydrophilic glycine and positive for other amino acids. The ΔΔsoln
S
0 values increase with an increase in the hydrophobicity of the amino acids. The Δ(Δsoln
G
0/T) values become more negative in the order Ala, Phe, Gly, His.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 711–714, April, 2007. 相似文献