共查询到20条相似文献,搜索用时 15 毫秒
1.
Pornpun Rattananakin Charles U. PittmanJr. Willard E. Collier Svein Saebø 《Structural chemistry》2007,18(3):399-407
Twelve push–pull ethylene derivatives, NH2CH=CHX, NH2C≡CCH=CHX, and −OCHX=CHX (with X=BH2, C≡N, NO2, and CH2
+) have been studied by ab initio calculations. The rotational barrier around the central double bond was chosen as a probe
for push–pull effects, as push–pull effects would remove electron density from the central double bond. The amount of reduction
of double bond character will increase with the contribution of the zwitterionic resonance hybrid structure. Complete geometry
optimizations and calculations of vibrational frequencies were performed for all minima and transition state structures of
these 12 systems. The calculations were carried out with the B3LYP and MP2 methods using the 6-311+G(d,p) and the 6-311++G(d,p)
basis sets. All the systems investigated exhibited properties consistent with push–pull effects such as elongated C=C double
bonds, dipolar electronic structures, and reduced barriers to internal rotation. 相似文献
2.
aatay DENGZ 《Turkish Journal of Chemistry》2021,45(5):1375
A series of new push–pull chromophores were synthesized in moderate to very high yields (65%–97%) by treating TCNE and TCNQ with alkynes substituted by electron-rich diethylaniline and polycyclic aromatic hydrocarbons. Some of the chromophores exhibit strong intramolecular charge-transfer bands in the near-IR region with λmax values between 695 and 749 nm. With the help of experimental and theoretical analysis, it is concluded that the trend in λ max values is affected by PAH substituents sterically, not electronically. Steric constraints led to the increased dihedral angles, reducing conjugation efficiencies. The absorption properties of push-pull compounds have been investigated in solvents possessing different polarities. All chromophores exhibited positive solvatochromism. As an additional proof of efficient charge-transfer in push–pull chromophores, quinoid character (dr) values were predicted using calculated bond lengths. Remarkably, substantial dr values (0.045–0.049) were predicted for donor diethylaniline rings in all compounds. The effects of various polycyclic aromatic hydrocarbons on optical and nonlinear optical properties were also studied by computational methods. Several parameters, such as band gaps, Mulliken electronegativity, chemical hardness and softness, dipole moments, average polarizability, first hyperpolarizability, were predicted for chromophores at the B3LYP/6-31++G(d,p) level of theory. The predicted first hyperpolarizability β(tot) values vary between 198 to 538 × 10–30 esu for the reported push–pull chromophores in this study. The highest predicted β(tot) value in this study is 537.842 × 10–30 esu, 8150 times larger than the predicted β(tot) value of benchmark NLO material urea, suggests possible utilization of these chromophores in NLO devices. The charge-transfer character of the synthesized structures was further confirmed by HOMO-LUMO depictions and electrostatic potential maps. 相似文献
3.
Jie Wu Shuixing Wu Yun Geng Guochun Yang Shabbir Muhammad Junling Jin Yi Liao Zhongmin Su 《Theoretical chemistry accounts》2010,127(4):419-427
Phosphole-based systems due to the unique electronic and optical properties have recently been paid much attention as optoelectronic
materials. In this work, the relationship among the electronic structure, charge injection, and transport was investigated
for five derivatives of dithieno[3,2-b:2′,3′-d]phosphole (systems 1–5). The structures of systems 1–5 in the ground (S0) and the lowest singlet excited (S1) states were optimized at the HF/6-31G* and CIS/6-31G* levels of theory, respectively. Based on these structures, electronic
spectra were calculated by time-dependent density functional theory. The simulated emission peaks of five phosphole derivatives
locating at the blue–green region (448–516 nm), are in good agreement with the experimental data. Compared with tris-(8-quinolinolate)
aluminum (III) (Alq3), normally used as an excellent electron transporter, systems 1–5 show a significant improvement in electron affinity (EA) due to σ*–π* hyperconjugation, which can effectively promote ability
of electron injection. The small differences between λ
h
and λ
e
for systems 1–5 (0.06–0.14 eV) facilitate charge transfer balance, which suggests systems 1–5 can act as potential ambipolar materials. Owing to good rigidity, low-lying LUMO levels, delocalized frontier molecular orbitals,
and the small reorganization energies, the five derivatives of dithieno[3,2-b:2′,3′-d]phosphole are expected to be high-efficiency blue materials in single-layer OLEDs. 相似文献
4.
Dmitry A. Sibgatulin Dmitry M. Volochnyuk Aleksander N. Kostyuk Sergey P. Ivonin Andriy V. Lapandin 《Monatshefte für Chemie / Chemical Monthly》2009,13(4):639-643
Abstract
The reaction of push–pull enamines with 1,2-biselectrophilic phenylglyoxal was investigated. Phenylglyoxal was found to react depending on the structure of the push–pull enamine, affording either a hydroxyalkylation product at the methyl group or the cyclic product via participation of the methyl group and the β-carbon of the enamine. 相似文献5.
V. Torres-Zúñiga O. G. Morales-Saavedra E. Rivera R. Castañeda-Guzmán J. G. Bañuelos R. Ortega-Martínez 《Journal of Sol-Gel Science and Technology》2010,56(1):7-18
SiO2-based bulk and film sol–gel hybrid materials were prepared with a family of novel liquid crystalline (LC) amphiphilic azo-dyes
bearing oligo(ethylene glycol) spacers (named here RED-PEG-n, n = 2, 3, 4, 6). The catalyst-free-sonogel route was implemented to produce optically active hybrid monoliths and spin-coated
films with these materials. Comprehensive morphological, thermal, photo-acoustic and spectroscopic sample characterizations
were performed in order to elucidate the physical properties of these novel compounds within the sonogel environment. Film
samples were also studied via the nonlinear optical (NLO) second harmonic generation (SHG)-Maker fringes technique. Results
show that the chromophores were homogeneously embedded within the highly pure SiO2-sonogel network, showing a clear thermotropic mesogenic behavior. The push–pull structure of the implemented azo-dyes allowed
effective electrically-induced monomeric alignment within the sonogel confinement; thus, stable quadratic NLO-SHG-activity
in the organic–inorganic film samples was achieved despite the lack of glass transition temperature (T
g
) of the guest LC-compounds. 相似文献
6.
To design innovative and novel optical materials with high mobility, two kinds of disubstituted derivatives for meridianal isomer of tris(8-hydroxyquinolinato)aluminum (mer-Alq3) with push–pull (X–Y) substituents have been designed. The structures of tris(4-X-6-Y-8-hydroxyquinolinato)aluminum (type 1) and tris(4-Y-6-X-8-hydroxyquinolinato)aluminum (type 2) (where X = –CH3/–NH2 and Y = –CN/–Cl) in the ground (S0) and first excited (S1) states have been optimized at the B3LYP/6-31G* and CIS/6-31G* level of theory, respectively. All the designed derivatives of type 1 show blue shift while most of the type 2 derivatives show red shift as compared to the mer-Alq3. The emitting color could be tuned from blue to red. We have explained the distribution of HOMOs and LUMOs on different individual ligands. The reorganization energies of tris(4-methyl-6-chloro-8-hydroxyquinolinato)aluminum (1), tris(4-methyl-6-cyano-8-hydroxyquinolinato) aluminum (2), tris(4-chloro-6-methyl-8-hydroxyquinolinato)aluminum (5) and tris(4-cyano-6-methyl-8-hydroxyquinolinato)aluminum (6) are comparable with mer-Alq3. Thus these derivatives might be good candidates for emitting materials possessing comparable charge carrier mobility as mer-Alq3. 相似文献
7.
The results of non empirical quantum-chemical calculations using the RHF/6-31G(d) and MP2/6-31G(d) methods do not agree with
proposals for the axial position of the H atom on the N atom in the piperidine molecule. According to RHF/6-31G(d) calculations
for the N-methylpiperidine molecule and its chloro-substituted derivatives an equatorially placed methyl group is energetically
more favored than an axial. The axial C-Cl and C-H bonds in these molecules are longer than the equatorial. The 35 Cl NQR frequencies for the axial Cl atoms are lower than the equatorial. The 35 Cl NQR frequency of the axial chlorine atom in 2-chloro-1-methylpiperidine is anomalously low. This is chiefly due to the
high population density of its p σ-orbital and this is a result of the polarization of the C-Cl bond via the N atom unshared
electron pair directly through the field. The effect of a similar unshared electron pair on the parameters of the C-Cl bond
in the ClCH2NH2 molecule has been studied by the RHF/6-31(g) method for different angles of rotation of the ClCH2 group around the C-N bond.
__________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 1044–1052, July, 2005. 相似文献
8.
Dmitry A. Sibgatulin Dmitry M. Volochnyuk Aleksander N. Kostyuk Sergey P. Ivonin Andriy V. Lapandin 《Monatshefte für Chemie / Chemical Monthly》2009,140(6):639-643
Abstract The reaction of push–pull enamines with 1,2-biselectrophilic phenylglyoxal was investigated. Phenylglyoxal was found to react
depending on the structure of the push–pull enamine, affording either a hydroxyalkylation product at the methyl group or the
cyclic product via participation of the methyl group and the β-carbon of the enamine.
Graphical abstract
相似文献
9.
Maurizio Casarin Andrea Vittadini Ulrich Schubert 《Monatshefte für Chemie / Chemical Monthly》2007,138(12):1217-1223
Summary. DFT calculations were carried out on Ti2(OCH3)8 (NH2CH3)2 and Ti2(OCH3)8(NH3)2, which are model compounds for the previously isolated amine adducts Ti2(OR)8(NH2
R′)2. The calculations show that the Ti–N bond strength is weak; however, coordination of the amine to the metal center is supported
by a N–H···O hydrogen bond of the amine with the neighboring alkoxo ligand. The Ti–N interaction is purely σ in nature, while
the Ti–O interactions include both σ and π contributions. The lowest unoccupied molecular orbitals are mainly localized on
Ti t2g-like orbitals. 相似文献
10.
Ab initio many-body perturbation theory (MP2/6-311++G(,dp)), density functional theory (B3LYP/6-31++G(d,p)) and self-consistent
reaction field (IEF-PCM UA HF/6-31G(d)) calculations have been used to study the CO2 capture reagents NH3, 2-hydroxyethylamine (MEA), diaminoethane (EN), 2-amino-1-propanol (2A1P), diethanolamine (DEA), N-methyl-2-hydroxyethylamine (N-methylMEA), 2-amino-2-methyl-1-propanol (AMP), trishydroxymethylaminomethane (tris), piperazine (PZ) and piperidine (PD).
This study involved full conformational searches of the capture amines in their native and protonated forms, and their carbamic
acid and carbamate derivatives. Using this data, we were able to compute Boltzmann-averaged thermodynamic values for the amines,
carbamates and carbamic acid derivatives, as well as equilibrium constants for a series of ‘universal’ aqueous capture reactions.
Important findings include (i) relative pK
a values for the carbamic acid derivatives are a useful measure of carbamate stability, due to a particular chemical resonance
which is also manifest in short computed N–CO2H bonds at both levels of theory, (ii) the computational results for sterically hindered amines such as AMP and tris are consistent
with these species forming carbamates which readily hydrolyse and (iii) the amine-catalysed reaction between OH− and CO2 to generate bicarbonate correlates with amine pK
a. Thermodynamic data from the ab initio computations predicts that the heterocycles PD and PZ and the acyclic sorbent EN are
good choices for a capture solvent. AMP and tris perform poorly in comparison. 相似文献
11.
Structure optimizations of the thiophene carbon–sulfur H2(C2S)
n
C2H2 (n = 1–20) were carried out using density functional theory calculations at the B3LYP/6-31G(d) level. The B3LYP/6-31G(d) geometrical
data for heptamer H2(C2S)7C2H2 and undecamer H2(C2S)11C2H2 are in good agreement with the X-ray crystallographic data for the helical (C2S)n
β-heptathiophene and β-undecathiophene, respectively. Structural and electronic properties of helical oligothiophenes obtained at the B3LYP/6-311++G(d,p)//B3LYP/6-31G(d)
level are reported. The strain energy formula of n oligothiophenes as a linear function of their molecular length was obtained. 相似文献
12.
Yu. L. Frolov A. V. Abramov N. N. Chipanina T. N. Aksamentova M. G. Voronkov 《Journal of Structural Chemistry》1999,40(6):849-854
Pentacoordinated silicon compounds of the series 4-XC6H4C(O)O(CH2)mSi(CH3)3-nFn (m = 1, 2; n= 1,2,3) with an intramolecular 0→Si bond are studied by ab initia and semiempirical (AMI) quantum chemical methods.
The results are compared with published experimental data. The C6H5C(O)OCH2SiF3 molecule is calculated in an RHF approximation using the 6–31G*basis set. The total energy of the molecule for its geometry
optimization is calculated by the MP2 method including electron correlation. This leads to considerably improved agreement
between the calculated coordination energy (25.3 kJ/mole) and the experimental value (28.5 kJ/mole). The geometry and the
dipole moment calculated by both ab initio (HF/6-31G*//HF/6-31G*, MP2/6-31G*//MP2/6-31G*) methods and by the AMI method are
in satisfactory agreement with the experimental data. 相似文献
13.
L. I. Belen'kii T. G. Kim I. A. Suslov N. D. Chuvylkin 《Russian Chemical Bulletin》2005,54(4):853-863
Data on the relative reactivities (substrate selectivity) of five-membered heterocycles in electrophilic substitution reactions
and positional selectivity (α : β ratio) in these reactions were analyzed. Unlike the substrate selectivity (pyrrole ≫ furan
> selenophene > thiophene) determined by the position of heteroatoms in the Periodic Table, the positional selectivity decreases
in the order corresponding to the change in the relative stability of the onium states of the elements (O+ < Se+ ≤ S+ < N+) and reflects the predominant role of heteroatoms in the stabilization of σ complexes formed upon β-substitution. These differences
in the positional selectivity of the parent heterocycles have a substantial effect on the orientation in electrophilic substitution
reactions in their derivatives and the corresponding benzoannelated systems. This interpretation was confirmed by ab initio quantum chemical calculations (RHF/6–31G(d) and MP2/6– 31G(d)//RHF/6–31G(d)) and density functional theory calculations (B3LYP/6–31G(d)).
Quantum chemical calculations were performed by the above-mentioned methods for model N-R-pyrroles (R = Me, Et, Pri, But, CH=CH2, C≡CH, Ph, PhSO2, and 4-O2NC6H4) and their α- and β-protonated σ complexes. The results of these calculations demonstrated that it is the steric factors
and charges on the β-C, α-C, and N atoms and the substituents at the N atom (the kinetic control), as well as the nature of
the electrophile, rather than the difference in the relative stabilities of the onium states of N+ (which depends on the nature of the substituent at the N atom and reflects the role of the heteroatom in stabilization of
σ complexes formed via β-substitution; the thermodynamic control) that are responsible for the type of orientation (α or β) that prevails.
Dedicated to Academician V. I. Minkin on the occasion of his 70th birthday.
__________
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 837–846, April, 2005. 相似文献
14.
Optimised conditions have been found for the separation of 3-carboxy-4-hydroxy-6-acetylaminoazo-benzene derivatives substituted
in the position 4′ (4′-R-CHAAB, where R=–H, –CH3, –OCH3, –Cl, –COCH3, –NO2 and –NHCOCH3) using reversed phase HPLC with a C18 chemically bonded stationary phase. Suitable mobile phases are mixtures of 0.01 mol/L
NaH2PO4 at pH 4 with methanol (1+1), 0.01 mol/L NaH2PO4 at pH 2 with acetonitrile (1+1) or 1% aqueous acetic acid with methanol (4+6). UV photometry is the most universal detection
technique and yields limits of detection around 10-6 mol/L. Direct anodic voltammetry on a glassy carbon fibre array detector yields lower limits of detection for –COCH3 derivatives and higher limits of detection for –NO2 and –NHCOCH3 derivatives. When the analytes are chemically reduced using zinc powder in acetic acid, the voltammetric detection has limits
of detection one order of magnitude lower than those obtained UV photometrically.
Received: 27 June 1996/Revised: 25 October 1996/Accepted: 3 November 1996 相似文献
15.
Muniz-Miranda M Del Rosso T Giorgetti E Margheri G Ghini G Cicchi S 《Analytical and bioanalytical chemistry》2011,400(2):361-367
We investigated the chemisorption of self-assembled monolayers of sulfur-functionalized 4-amino-7-nitrobenzofurazan on gold
and silver nanoisland films (NIFs) by means of surface-enhanced fluorescence (SEF) and surface-enhanced Raman scattering (SERS).
The ligand is a push–pull molecule, where an intramolecular charge transfer occurs between an electron-donor and an electron-acceptor
group, thus exhibiting nonlinear optical properties that are related to both SERS and SEF effects. The presence of different
heteroatoms in the molecule ensures the possibility of chemical interaction with both silver and gold substrates. The SERS
spectra suggest that furazan is bound to silver via lone pairs of the nitrogen atoms, whereas the ligand is linked to gold
via a sulfur atom. Silver NIFs provide more efficient enhancement of both fluorescence and Raman scattering in comparison
with gold NIFs. The present SEF and SERS investigation could provide useful information for foreseeing changes in the nonlinear
responses of this push–pull molecule. 相似文献
16.
I. S. Ignat’ev M. G. Voronkov T. A. Kochina D. V. Vrazhnov 《Russian Journal of General Chemistry》2010,80(11):2274-2282
Quantum-chemical study of the electronic structure and the equilibrium geometry of the molecules X4−n
M(OCH2CH2)
n
NH3−n
and cations X3−n
[M(OCH2CH2)
n
NH3−n
]+ (M = Si, Ge; X = F, H; n = 1–3) is performed by the B3LYP method using the cc-PVDZ basis set. It is shown that for X = F the strength of the coordination
bond N→M increases with the number of the cycles (n), while for X = H, on the contrary, decreases, that is, the strength of the N→M bond increases with the total electronegativity
of the substituents surrounding atom M. Effect of the number of the coordination cycles on the strength of the N→M bond in
the cations is negligible. The obtained results agree with the experimental data on the structure and spectral properties
of the studied compounds. 相似文献
17.
1-Aminocyclopropanecarboxylic acid (Ac3c) is a constrained α amino acid residue that exhibits peculiar conformational characteristics. The aim of the present study
is to provide a deeper understanding of these features to be used as guidance to decide when to choose Ac3c as a building block for the design of peptide and protein surrogates. The whole Ramachandran plot of the Ace-Ac3c-NCH3 dipeptide was investigated at the Hartree–Fock level using a 6-31G(d) basis set and the most favorable structures were assessed
on this surface by energy minimization. These results were subsequently used as a reference to generate specific molecular
mechanics parameters for Ac3c compatible with the parm94 set of the AMBER force field. The effect of water as a solvent on the conformational profile
of the dipeptide was also assessed using the Miertus–Scrocco–Tomasi self-consistent reaction-field model at the Hartree–Fock
level using a 6-31G(d) basis set and using the AM1 semiempirical method. The conformational profile of the Ac3c dipeptide can be characterized by two symmetric low-energy regions for values of φ around ±80° with a wide range of values
for ψ ranging from −40 to 180°, with the lower areas located at low values of ψ. Solvent effects do not alter the features
of the conformational map, but a shift of the two absolute minima to (φ, ψ) values near (±90°, 0°) can be observed. These
results are in accord with all experimental evidence and with the known tendency of Ac3c to induce β-turn conformations in peptides.
Received: 19 March 1999 / Accepted: 10 June 1999 / Published online: 9 September 1999 相似文献
18.
Conditions for silylation of benzidine (BZ) and 3,3′-dichlorobenzidine (DCBZ) have been optimized. Reactivity, repeatability,
and derivative stability were compared for the silylating reagents N-Methyl-N-(trimethylsilyl)trifluoroacetamide (MSTFA) and N-Methyl-N-(tert-butyldimethylsilyl)trifluoroacetamide (MTBDMSTFA) and the catalysts 3% trimethylsilylimidazole (TMS-I) and 0.3% NH4-I–dithioerythritol. The results showed that derivatization with MTBDMSTFA/NH4-I containing 0.1 mg dithioerythritol was superior to other methods. The silylation conditions selected were reaction with
(MTBDMSTFA)–NH4I, 1000:3, with catalysis by dithioerythritol, at 80 °C for 80 min. The TBDMS derivatives of BZ and DCBZ had very good chromatographic
properties and very sensitive detection was achieved by gas chromatography with electron-impact ionization mass spectrometry
(GC-EIMS). Simultaneous determination of BZ and DCBZ in water was developed on the basis of the TBDMS derivatives. Deuterated
BZ (d8-BZ) was chosen as internal standard (IS) for analysis of water samples. BZ and DCBZ were extracted from water at pH
8.5 with dichloromethane and the extract was then dried and silylated. Recoveries of BZ and DCBZ were approximately 102 and
103% at a concentration of 2.0 ng mL−1. The coefficients of variation for BZ and DCBZ were less than 9 and 4% at concentrations of 0.2 and 0.5 ng mL−1, respectively. The method detection limits for 200 mL water were 0.004 ng mL−1 for BZ and 0.02 ng mL−1 for DCBZ. 相似文献
19.
J. M. Garrigues Z. Bouhsain S. Garrigues M. de la Guardia 《Analytical and bioanalytical chemistry》2000,366(3):319-322
A new procedure has been developed for the FT-IR determination of caffeine in roasted coffee samples. The method involves
wetting the coffee samples with a 0.25 M aqueous NH3 solution, extracting the caffeine with CHCl3, and measuring absorbance at 1659 cm–1 using a baseline established between 1900 and 830 cm–1. The procedure proposed is fast, only requiring a total extraction time of 16 min for each sample, and provides a drastic
reduction of the organic solvent consumed, from the 200 mL diethyl ether and 50 mL CHCl3 required for each sample by the reference chromatographic UV-spectrometric determination to only 5 mL CHCl3. The method provides a limit of detection of the order of 3 mg L–1 caffeine and a relative standard deviation of 0.4% for 3 independent analyses of a sample containing 18.6%mg/g caffeine.
The accuracy of the FT-IR procedure was evaluated from recovery experiments on spiked samples providing values from 94.4 to
100.1% and from the comparison of results found for a series of commercial samples, by both FT-IR and the official reference
procedure.
Received: 9 July 1999 / Revised: 23 September 1999 / /Accepted: 24 September 1999 相似文献
20.
The tetrazole is an important functionality of the most of energetic materials due to 80% nitrogen content, stability, and
high enthalpy of formation. The present structure–property relationship study focuses on the optimized geometries of tetrazole
derivatives obtained from density functional theory (DFT) calculations at B3LYP/6-31G* levels. The heat of formation (HOF)
of tetrazole derivatives have been calculated by designing the appropriate isodesmic reactions. The increase in nitro groups
on azole rings shows the remarkable increase in HOF. Density has been predicted by using CVFF force field. Increase in the
nitro group increases the density. Detonation properties of the designed compounds were evaluated by using the Kamlet–Jacobs
equation based on predicted densities and HOFs. Designed tetrazole derivatives show detonation velocity (D) over 8 km/s and detonation pressure (P) of about 32 GPa. Thermal stability was evaluated via bond dissociation energies (BDE) of the weakest C–NO2 bond at B3LYP/6-31G* level. Charge on the nitro group has been used to assess the sensitivity correlation. Overall, the study
implies that designed compounds of this series are found to be stable and expected to be the novel candidates of high energy
materials (HEMs). 相似文献