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1.
The absorption bands in the UV spectra of isomeric nitropyrazoles were assigned by the calculations in the semiempirical AMI
(CI) approximation. The long-wave absorption of nitropyrazoles is caused by π→π* and η0→π* transitions. The charge-transfer band is the most intense. The π→π* transitions undergo a considerable bathochromic shift
in the deprotonation. The first ionization potential (PI) of the 4-nitropyrazole anion was estimated from the empirical dependence
of the energy of the excited π-state on PI of alkyl-substituted 4-nitropyrazoles. The PI of the 4-nitropyrazole anion is 3
eV lower than that of a neutral molecule. This is evidence for a substantial destabilization of the boundary β-orbital in
the heterolytic cleavage of the N−H bond. The analysis of the UV and NMR spectra of 3(5)-nitropyrazole confirms the viewpoint
that the 3-nitro tautomer predominates in solution.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya. No. 2, pp. 310–314, February, 1997. 相似文献
2.
This paper presents the investigations of the electronic and vibrational spectra of 2,4,6-trichloropyrimidine and 6-chloro
2,4-dimethoxypyrimidine. The electronic spectra have been recorded in the liquid and vapour states in the region 50000-28000
cm−1. Then-π and π-π transitions are classified in each case. Infrared absorption spectra of 2,4,6-trichloropyrimidine in nujol have
been recorded in the region 4000-400 cm−1. It is concluded that substituents like Cl or OCH3 do not have much influence on thesp
2 electron of the nitrogen atom of the ring. From infrared studies the mass-dependent modes and the modes insensitive to substitution
have been pointed out. The assignments are tentative and are based on the group frequency approach and data available for
similar molecules. 相似文献
3.
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
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.
The absorption spectra of polyaniline (PAN) films obtained by electrochemical polymerization on transparent SnO2-glass electrodes are analyzed. The spectra are recorded at steady-state potentials of 0.0 to 0.8 V (Ag/AgCl) in an aqueous
HC1 solution. Individual absorption bands, isolated by the Alentsev-Fok method, include both earlier known bands and some
new absorption bands. The former correspond to π-π* transitions in the benzenoid rings (300-320 nm), radical cations (∼435 nm), localized polarons (∼755 nm), and quinoid structures
(∼655 nm). By comparing these results with the spectroelectrochemical data obtained earlier for electrochemically synthesized
PAN in solutions of various acids and for vacuum-deposited PAN, the newly found bands are assigned to different intermolecular
interactions, specifically, a donor-acceptor coupling of the quinoid moieties with counter anions (at 570 nm) and an electron
exchange between highly conducting domains of the film (∼900 nm) 相似文献
6.
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
7.
A. V. Chernyshev I. V. Dorogan N. A. Voloshin A. V. Metelitsa V. I. Minkin 《Russian Chemical Bulletin》2011,60(3):456-464
The spectral and kinetic properties of 5-(4,5-diphenyl-1,3-oxazol-2-yl)spiro[indoline-naphthopyran] derivatives were studied
by experimental and theoretical methods. The additional long-wavelength maximum in the absorption spectra of compounds studied
is due to the introduction of a diphenyloxazole fragment and corresponds to a π-π* electronic transition with a partial charge
transfer character. Substituents have little effect on the kinetic parameters of the spironaphthopyrans studied. 相似文献
8.
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
9.
Gökhan Alpaslan Hasan Tanak Ayşen Alaman Ağar Ahmet Erdönmez Şamil Işık 《Structural chemistry》2010,21(5):1027-1036
The Schiff base compound (E)-2-(1-(2-(4-methylphenylsulfonamido)ethyliminio)ethyl) phenolate has been synthesised and characterized
by IR, UV–Vis, and X-ray single-crystal determination. Ab initio calculations have been carried out for the title compound
using the density functional theory (DFT) and Hartree–Fock (HF) methods at 6-31G(d) basis set. The calculated results show
that the DFT/B3LYP and HF can well reproduce the structure of the title compound. Using the TD-DFT and TD-HF methods, electronic
absorption spectra of the title compound have been predicted and a good agreement with the TD-DFT method and the experimental
ones is determined. Molecular orbital coefficient analyses reveal that the electronic transitions are mainly assigned to n → π* and π → π* electronic transitions. To investigate the tautomeric stability, optimization calculations at B3LYP/6-31G(d)
level were performed for the NH and OH forms of the title compound. Calculated results reveal that the OH form is more stable
than NH form. In addition, molecular electrostatic potential and NBO analysis of the title compound were performed at B3LYP/6-31G(d)
level of theory. 相似文献
10.
Tarek M. El-Gogary Mostafa A. Diab Shreen F. El-Tantawy 《Monatshefte für Chemie / Chemical Monthly》2006,38(12):1027-1042
Equilibrium constants and molar extinction coefficients for 1:1 charge-transfer complexes between 2-hydroxyaniline (HA), 5-chloro-2-hydroxyaniline (CHA), and 4-bromo-2,6-dimethylaniline (BMA) as donors and iodine, as a typical σ-acceptor were determined spectrophotometrically in chloroform, dichloromethane, and
carbontetrachloride solutions. Spectral characteristics and formation constants are discussed in terms of donor molecular
structure and solvent polarity. The stoichiometry of the complexes was established to be 1:1. For this purpose, optical data
were subjected to the form of the Rose-Drago equation for 1:1 equilibria. Electronic absorption spectra of the studied anilines were measured in different solvents. Spectral
data were reported and band maxima were assigned to the appropriate molecular orbital transitions (π–π* and n–π* electronic transition). Solvent effects on the electronic transitions were discussed. Optimized geometry of the studied anilines
was obtained at B3LYP/6-31 + G(d). The effect of the electronic factors of the substituents on the geometrical parameters
of the ring has been explored. Geometrical values of the ring deviate from the regular hexagonal ring. Intramolecular H-bonds
in HA and CHA have been computed at B3LYP/6-31 + G(d) and MP2/6-31 + G(d) levels. The H-bonding distance was calculated to be 2.105 ? in
HA and 2.127 ? in CHA. 相似文献
11.
Tarek M. El-Gogary Mostafa A. Diab Shreen F. El-Tantawy 《Monatshefte für Chemie / Chemical Monthly》2006,137(8):1027-1042
Summary. Equilibrium constants and molar extinction coefficients for 1:1 charge-transfer complexes between 2-hydroxyaniline (HA), 5-chloro-2-hydroxyaniline (CHA), and 4-bromo-2,6-dimethylaniline (BMA) as donors and iodine, as a typical σ-acceptor were determined spectrophotometrically in chloroform, dichloromethane, and
carbontetrachloride solutions. Spectral characteristics and formation constants are discussed in terms of donor molecular
structure and solvent polarity. The stoichiometry of the complexes was established to be 1:1. For this purpose, optical data
were subjected to the form of the Rose-Drago equation for 1:1 equilibria. Electronic absorption spectra of the studied anilines were measured in different solvents. Spectral
data were reported and band maxima were assigned to the appropriate molecular orbital transitions (π–π* and n–π* electronic transition). Solvent effects on the electronic transitions were discussed. Optimized geometry of the studied anilines
was obtained at B3LYP/6-31 + G(d). The effect of the electronic factors of the substituents on the geometrical parameters
of the ring has been explored. Geometrical values of the ring deviate from the regular hexagonal ring. Intramolecular H-bonds
in HA and CHA have been computed at B3LYP/6-31 + G(d) and MP2/6-31 + G(d) levels. The H-bonding distance was calculated to be 2.105 ? in
HA and 2.127 ? in CHA.
Abstracted from her M.Sc. thesis 相似文献
12.
Adiabatic excitation energies, excited state geometries, excited state charges, bond orders and dipole moments have been obtained
for HCN, CO2,H2CO, HFCO, F2CO, ethylene, trans-butadiene, furan, pyrrole and uracil using the SINDO1 semi-empirical method with configuration interaction.
Our results generally agree with those ofab initio calculations and experiment satisfactorily. Geometry optimization is found to mix configurations differing in their allowedness
in vertical excitation from the ground state, which in turn helps in the assignment of spectral transitions. TheV excited singlet state of trans-butadiene and various excited states of furan, pyrrole and uracil have been found to be appreciably
non-planar. The single and double CC bonds are found to exchange positions due to the lowest triplet and singlet transitions
of furan and pyrrole. The first triplet and first singlet transitions of uracil have been found to be of π-π* and π-σ* types
respectively in agreement with recent experimental findings.
On leave of absence from the Department of Physics, Banaras Hindu University, Varanasi-221005, India 相似文献
13.
Mono-, bi-, and tetranuclear cyclopalladized complexes based on 2-(2-thienyl)pyridine and 2-phenylpyridine with pyridine and
4,4′-bipyridyl were prepared and characterized by the methods of 1H NMR, electron absorption and emission spectroscopy, and also by the voltammetry method. The values of the coordination-induced
shifts of proton in the ligands of the complexes were determined; the upfield displacement of chemical shifts of protons of
the cyclopalladized ligand nearest to the metal was assigned to the anisotropic action of a ring current of the pyridine rings
orthogonal to the coordination plane in 4,4′-bipyridyl and pyridine. Long-wave absorption bands of the complexes were assigned
to the spin-allowed optical d-π charge-transfer transitions, and the bands of the low-temperature phosphorescence, to the intraligand π-πNyyC* transitions. Three waves of the reduction of the complexes were assigned to the ligand-centered processes of successive electron
transfer on π* orbitals preferentially localized on coordinated pyridine and cyclopalladized ligands. 相似文献
14.
G. N. Ten V. V. Nechaev V. I. Berezin V. I. Baranov 《Journal of Structural Chemistry》1997,38(2):262-267
The vibrational spectra of adenine and its deuterium-substituted analogs are calculated in the valence force field approximation.
The frequencies and forms of normal vibrations of the molecule at 1700–300 cm-1 are interpreted.
Translated fromZhumal Struktumoi Khimii, Vol. 38, No. 2, pp. 324–333, March–April, 1997. 相似文献
15.
A series of porphyrins with tolyl and naphthyl substituents at themeso positions, their octabromoderivatives (OBP) with Br substituents at β-pyrrole positions are synthesised and characterised
by chemical analysis,1H NMR and electronic spectral studies. It is seen that all the OBPs exhibit pronounced red shifts in both the Soret andQ bands of their electronic spectra compared to their non-brominated form in various polar and nonpolar solvents, the energy
difference Δv being in the range 2300–2700 cm−1. The high energyB band of naphthyl porphyrins (both brominated and nonbrominated) are found to be more red-shifted than that of tolyl porphyrins,
owing to the noticeable mesomeric effect of the naphthyl groups. Detailed spectral studies reveal that while none of the nonbrominated
porphyrin show solvent-dependent change in theirB andQ bands, all the OBPs manifest significant shifts depending on the nature of solvents. Solvent-solute interaction can be considered
to be of strong dipole-dipole nature for OBPs with polar solvents and of π-π type with aromatic non-polar solvents. In the
brominated form we find two categories of porphyrins exhibiting distinctly different absorption phenomena in aromatic solvents.
The OBPs havingmeso-groups not shielding the porphyrin π-framework exhibit additional absorption peaks (split Soret peaks and broadened Q bands) in
some aromatic solvents. This could be explained in terms of π-π type donor-acceptor (DA) complex formation between such bromoporphyrins
(acceptor) and the aromatic solvent molecules (donor) that is not possible for OBPs that have bulkymeso groups that block the approach of aromatic solvent molecules close to the porphyrin framework 相似文献
16.
Sadia Ameen M. Shaheer Akhtar Young Soon Kim O-Bong Yang Hyung-Shik Shin 《Colloid and polymer science》2011,289(4):415-421
The polyaniline/zinc oxide (PANI/ZnO) nanocomposites were prepared by in situ polymerization of aniline monomer with ZnO nanomaterials
and applied as a photocatalyst for the degradation of methylene blue (MB) dye. The morphological observations elicited the
agglomerations of PANI sheets which occurred due to the interaction between PANI and ZnO nanomaterials in PANI/ZnO nanocomposites.
As compared to pristine PANI, the UV–vis spectra exhibited that the absorption peak of π–π* transitions considerably shifted to higher wavelength at 360 nm from 325 nm in the nanocomposites. The photocatalytic activity
results indicated the substantial degradation of MB dye by ~76% over the surface of PANI/ZnO nanocomposite catalyst under
light illumination. The PANI/ZnO nanocomposites showed three times higher photocatalytic activity to MB dye degradation compared
to pristine PANI might due to high photogenerated electron (ē)–hole (h+) pairs charge separation. 相似文献
17.
The absorption spectra of decapentaene are analyzed and calculated using the available efficient methods of calculating the
matric elements of the vibronic problem, a new parametric method for determining the potential surfaces of excited molecules,
and a fragmentation approach to the design of molecular models. Good agreement for the fine vibrational structure of the calculated
and experimental spectra (differences between the main band frequencies and intensities less than 20 cm−1 and 10%, respectively) is obtained without correcting the parameters of the method. The mechanisms of excitation-induced
structural changes in linear polyenes and the effect of bond angle changes on the vibrational structure of the spectrum are
revealed. A new interpretation of the absorption spectrum of decapentaene in an argon matrix is proposed [J. Mol. Spectrosc.,114, 54–59 (1985)]. It is shown that the parametric method allows quantitative prediction of fine structure for the vibronic
spectra of complex molecules.
K. A. Timiryazev Moscow Agricultural Academy. Translated fromZhurnal Strukturmoi Khimii, Vol. 37, No. 6, pp. 1031–1039, November–December, 1996.
Translated by I. Izvekova 相似文献
18.
Three new squarate salts were synthesized and combined with experimental and theoretical study on molecular, vibrational,
and electronical properties. Squaric acid was crystallized as HSQ− [SQ: squarate] monoanion in [(C13H12NO2)(HC4O4)] (I), as uncharged H2SQ in [(C5H5N3O)(H2C4O4)] (II), and as SQ2− dianion form in [C6H9N2)2(C4O4)] (III). They crystallize in the triclinic and monoclinic crystal system with space group P−1, P21/c, and P21/c, respectively. Crystal structure analysis reveals that, far from forming discrete ionic species in (I) and (II), it is likely
that there is large degree of proton sharing between the two hydrogen squarate anions in (I) and between the neutral moieties
in (II), with the H atom lying almost symmetrically between the donor and acceptor sites, as evidenced by the long O–H and
N–H bonds and short H···O distances. Ab initio calculations have been carried out for three compounds by using DFT/B3LYP and
HF methods at 6-31++G(d,p) basis set. Although the supramolecular interactions have some influences on the molecular geometry
in solid state phase, calculated data show that the predicted geometries can reproduce the structural parameters. The results
of the optimized molecular structure for three compounds obtained on the basis of two models are presented and compared with
the experimental X-ray data. Calculated vibrational frequencies are consistent with each other and experimental IR data. The
theoretical electronic absorption spectra have been calculated by both TD–DFT and HF–CIS methods. Molecular orbital coefficients
analysis suggest that the electronic transitions are mainly assigned to n → π* and π → π* electronic transitions. 相似文献
19.
A new algorithm for automatic assignment of the resolved vibrational structure of the electronic absorption spectra of diatomic
and polyatomic molecules is suggested.
Translated fromZhurnal Struktumoi Khimii, Vol. 38, No. 2, pp. 363–368, March–April, 1997. 相似文献
20.
A cholesterol-based organogelator bearing an anthraquinone imide(AQI) group was synthesized and characterized.It self-assembled into chiral gels in acetonitrile at low concentrations,which displayed a combination of electrochromic and chiroptical properties.Upon electrochemical reduction at -700 mV,the gel exhibited new absorption bands at around 820 nm corresponding toπ~*-π~*(SOMO→LUMO) transitions of the radical anion of AQI and strong negative Cotton effects in the same spectral region.With further reduction at -1000 mV,a new CD band with a negative Cotton effect in the range from 500 nm to 800 nm appeared concomitant with the variation of absorption spectrum.Thus, with the use of electrochromic AQI chromophore as a switch-responsive unit and the stable gel of compound N-[3β-cholest-5 -en-3-yl N-(2-aminoethyl) carbamate]anthraquinone-2,3-dicarboxylic imide as a chiral scaffold,a redox-triggered chiroptical switch operating in visible and near-infrared region was realized. 相似文献