Infrared and Raman spectra,DFT investigation of the tautomerism,conformational equilibrium,structure and vibrational assignment of 1-(2-benzothiazolyl)-3-methyl pyrazol-5-one

The low energy conformations of the three tautomers, imine-enol, enamine-keto and imine-keto forms of the title compound have been determined at the B3LYP/6-31 + G(d) level of theory using the relaxed PES scan method and their geometries have been refined at B3LYP/6-311 + G(d,p) and PBE0/6-311 + G(d,p) levels. The results show that the title compound exists in the imine-enol tautomeric form, in contrast to the enamine-keto form which exists in the solid crystalline state, followed by enamine-keto and imine-keto forms with extremely low abundances. The geometry parameters of all tautomeric forms calculated at PBE0/6-311 + G(d,p) and B3LYP/6-311 + G(d,p) levels have been compared with those from the experimental X-ray diffraction. The vibrational (FT-IR and Raman) spectroscopic studies of the most stable tautomer, enamine-keto form have been carried out. The assignment of the fundamental bands observed in the IR and Raman spectra have been facilitated by the SQM force field procedure. The frequencies from SQM procedure have a very good fit to the experimental ones. The total root-mean-square error is only ca. 11 cm⁻¹.     

High-resolution NMR spectra of fluorene and its derivatives: VI—1-methylfluorene,truxene and decacyclene

The overlapping spin systems in the 220 MHz ¹H spectra of 1-methylfluorene (1) in carbon disulphide and deuteriated chloroform solutions have been analysed separately and refined by LAOCOON with the aid of methyl- and methylene-decoupled spectra. Ortho-coupling constants in the 6-membered rings are similar to each other and to those in fluorene (4). Solvent and concentration shifts suggest loose pairing of solute molecules. 220 MHz ¹H spectra of α-truxene (2) in carbon tetrachloride and deuteriated nitrobenzene, 220 MHz ¹H spectra of decacyclene (3) in carbon tetrachloride, and 90 MHz FT ¹H spectra of 3 in deuteriated chloroform show steric deshielding; the solvent dependence of shifts also suggests solute pairing in 2. Shifts in ¹H decoupled 22.6 MHz ¹³C spectra of 2 in deuteriated chloroform were assigned with the aid of Cr(acac)₃ relaxation agent.     

Modelling the vibrational behaviour of the cyclic carboxylic acid dimer. SQM force field of the formic acid dimer

The vibrational behaviour of the cyclic carboxylic acid dimer is modelled through the scaled quantum mechanical (SQM) force field of the cyclic formic acid dimer. The results indicate that the SQM force field technique is very well applicable to hydrogen bonded molecules. The frequency shifts observed on hydrogen bonding can be related to the shifts observed on lowering the temperature. This study also confirms that a clear distinction between cyclic carboxylic acid dimers and catamers can be made through the difference between infrared and Raman frequencies, and it is proved here that these conditions are also valid for weaker hydrogen bonded cyclic carboxylic acid dimers.     

Vibrational analysis of 3-trifluoromethylphenol

The molecular geometry and molecular vibrations of 3-trifluoromethylphenol have been investigated by means of quantum chemical calculations and vibrational spectroscopy. The computations indicated the preference of the conformer with the OH hydrogen pointing in the direction of the trifluoromethyl group by 0.9 kJ/mol with respect to the anti conformer. FT-IR spectra of the vapour and CCl₄ solution as well as FT-IR and FT-Raman spectra of the pure liquid have been recorded in the range of 4000–150 cm⁻¹. The interpretation of the spectra was based on a scaled quantum mechanical (SQM) analysis for which the initial force field was calculated at the Becke3-Lee-Yang-Parr (B3LYP) DFT level supplemented with a 6-311++G** basis set. Using 11 scale factors refined in the present study an rms deviation of 7.6 cm⁻¹ between the experimental and SQM frequencies has been achieved. On the basis of the computations 40 of the total of 42 fundamentals of the title compound have been assigned.     

Hydrogen bonding and molecular vibrations of 2,5-dihydroxy-1,4-benzoquinone

Intramolecular hydrogen bonding in 2,5-dihydroxy-1,4-benzoquinone has been investigated by means of quantumchemical calculations and vibrational spectroscopy. Both computations at the MP2/6-31+G** level as well as FT-IR and FT-Raman spectra are in agreement with the predominance of the C_2h conformer with two intramolecular hydrogen bonding interactions. The spectra were interpreted with the aid of normal coordinate analysis based on a scaled Becke3–Lee–Yang–Parr/6-31G* density functional force field. The general scale factors introduced recently by Rauhut and Pulay for this theoretical level allowed a reliable assignment of most of the fundamentals. The scale factors for vibrations affected strongly by the intramolecular hydrogen bonding interaction needed some adjustment and hence were re-optimized in the present study. The final scaled force field reproduced the experimental frequencies of the molecule by a weighted mean deviation of 8.8 cm⁻¹. Based on the calculated results, 32 from a total of 36 fundamentals were assigned in the vibrational spectra of 2,5-dihydroxy-1,4-benzoquinone revising and extending the assignments of earlier less sophisticated investigations.     

Vibrational spectra of 1,1,3,3-tetramethyl-2-nitroguanidine and their interpretation with the use of scaling of quantum-chemical force field

The IR (4000–50 cm⁻¹) and Raman (3500–170 cm⁻¹) spectra of solid 1,1,3,3-tetramethyl-2-nitroguanidine (TMNG) were obtained. The spectra were interpreted using the scaling of the TMNG quantum-chemical force field in the B3LYP/6-311G(d,p) approximation. Transferable scale factors necessary for the interpretation of spectra of more complex related compounds were determined. The scaled harmonic force field is supposed to be used in the analysis of the available gas-phase electron diffraction data for TMNG. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 495–498, March, 2008.     

Vibrational spectra and force constants ofS-methyl-N,N-dimethyldithiocarbamate

The IR and Raman spectra ofS-methyl-N,N-dimethyldithiocarbamate were studied in different phase states. The frequencies and vibration modes of normal vibrations were analyzed, and the erroneous assignments made in some previous works were corrected. The force constants of the molecule were estimated using the model of the generalized valenceforce field.Translated fromIzyestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1108–1110, June, 1995.This work was carried out with partial financial support from the International Science Foundation.     

Kinetics and thermal properties of epoxy resins based on bisphenol fluorene structure

The fluorene-containing epoxy, diglycidyl ether of 9,9-bis(4-hydroxyphenyl) fluorene (DGEBF) was synthesized by a two-step reaction procedure. In order to investigate the relationship between fluorene structure and material properties, DGEBF and a commonly used diglycidyl ether of bisphenol A (DGEBA) were cured with 4,4-diaminodiphenyl methane (DDM) and 4,4-(9-fluorenylidene)-dianiline (FDA). The curing kinetics, thermal properties and decomposition kinetics of these four systems (DGEBA/DDM, DGEBF/DDM, DGEBA/FDA, and DGEBF/FDA) were studied in detail. The curing reactivity of fluorene epoxy resins was lower, but the thermal stability was higher than bisphenol A resins. The onset decomposition temperature of cured epoxy resins was not significantly affected by fluorene structure, but the char yield and T_g value were increased with that of fluorene content. Our results indicated that the addition of fluorene structure to epoxy resin is an effective method to improve the thermal properties of resins, but excess fluorene ring in the chain backbone can depress the curing efficiency of the resin.     

Vibrational spectra of trinitromethane derivatives

Spectroscopic parameters of trinitromethane derivatives RC(NO₂)₃ (R = F, Cl, Br, I, NC, NF₂, N₃) were determined. Vibrational frequencies and modes were calculated and the assignment of experimental spectra was performed. Spectral features due to the mutual influence of the C(NO₂)₃ group and other atomic groups and particular atoms were revealed.     

Synthesis,gas barrier and thermal properties of polyimide containing rigid planar fluorene moieties

In order to obtain pristine polyimides with high barrier properties, pyromellitic dianhydride (PMDA) and 9H-fluorene-2,7-diamine (FDA) containing rigid planar fluorene moieties were used to prepare polyimide (FPI) via a conventional two-step polymerization process in this paper. The synthesized polyimide shows good barrier properties, with oxygen transmission rate (OTR) and water vapor transmission rate (WVTR) low to 1.01 cm³ m^?2 day^?1 and 2.35 g m^?2 day^?1, respectively. The effect of rigid planar structure in main chain on the barrier properties of polyimide was studied by means of wide angle X-ray diffractograms (WAXD), molecular dynamics simulations and positron annihilation lifetime spectroscopy (PALS), which was rarely reported before. The results reveal that the good barrier properties of FPI are mainly due to the high crystallinity, high chain rigidity and low free volume, which are resulted from the rigid planar structure. Additionally, the polyimide exhibits excellent thermal and dimensional stability with 5 wt% loss temperature of 519°C, glass transition temperature of 370°C and coefficient of thermal expansion (CTE) of 5.72 ppm/K. The good gas barrier and thermostability endow the polyimide with promising potential in flexible electronics encapsulation applications.     

Design, synthesis and redox properties of a fluorene platform linking two different Bodipy dyes

Several new fluorophores have been prepared by grafting boradiazaindacene (red absorbing) and/or styrylboradiazaindacene (blue absorbing) units as terminal energy acceptors onto a fluorene-derived platform. In one case, an amino-bis(bipyridine) pocket has been attached to enable strong binding of transition metal ions. The stepwise syntheses were largely based on Pd-catalysed cross-coupling reactions. The electrochemistry of the dyes has been analysed by reference to the properties of the various synthetic intermediates, protonation of the tertiary amine site present in the bis(bipyridine) species enabling processes involving this centre to be distinguished from those associated with the boradiazaindacene (Bodipy) unit.     

Ab initio vibrational analysis of hexafluoroethane C2F6

Quantum mechanical geometry optimizations and the calculation of vibrational frequencies of hexafluoroethane have been performed at the HF/6-31G*, MP2/6-31G*, CCSD/cc-pVDZ, and B3LYP/6-31G* levels. The force fields obtained were scaled. The necessity is stressed of carrying out the detailed analysis of the vibrational spectra of small reference molecules to determine sets of scale factors which are transferable to quantum mechanical force fields of large molecules for the purpose of predicting their vibrational spectra.     

Vibrational Spectra, Assignment, Conformational Stability and Ab Initio/DFT Calculations for 1-Nitropropane

The infrared spectra (4000–400 cm^{– 1}) of solid and the Raman spectra (3500–30 cm^{– 1}) of liquid and solid 1-nitropropane, CH₃CH₂CH₂NO₂, have been registered. Both the trans and gauche conformers have been identified in the fluid phase, while the trans form remains in the stable solid. Temperature dependence (190–230K) of the liquid 1-nitropropane Raman spectra has been carried out. From these data, the enthalpy difference was determined to be 870 ± 105 J-mol^–1, with the gauche conformer being the more stable rotamer. Ab initio and DFT calculations at different levels of approximation (HF, MP2, B3LYP, B3PW91) gave optimized geometries, harmonic force fields, and vibrational frequencies for the trans and gauche conformers. All the calculations (except the B3PW91/6-31G* level) predicted gauche as the low-energy conformer. Theoretical force constants are analyzed for formulating constraints in the molecular force field model of 1-nitropropane.     

Synthesis and photoluminescence stability of non-conjugated polymers based on fluorene and benzoxazole

A kind of non-conjugated blue luminescent polymer based on fluorene and benzoxazole was synthesized via solution condensation polymerization from 2,2-bis(3-amino-4-hydroxyphenyl)-propane and 2,7-dicarboxyl-9,9-dioctyl-fluorene and was characterized with H NMR, FT-IR, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), UV-vis absorption and photoluminescence (PL) spectroscopy. The polymer displayed the maximum photoluminescence emission peak at 415 nm and showed high PL spectroscopic stability. The green-to-blue emission intensity ratio I_Green/I_Blue is only 0.073 even after thermal annealing at 150 °C for 30 h. After being exposed to UV light for 30 min, no bathochromic emission or obvious crosslink is observed. The common phenomenon of greenish blue emission of fluorene-based polymer around 525 nm has been effectively restrained in this polymer by introducing the isopropylidene group into the backbone of polymer.     

分子力场进展

分子力学（简称ＭＭ）是近年来化学家常用的一种计算方法。与量子力学从头计算和半经验方法相比，用分子力学处理大分子可以大大节省计算时间，而且，在大多数情况下，用分子力学方法计算得到的分子几何构型参数与实验值之间的差值可在实验误差范围之内。所以，分子力学是研究生物化学体系的有效和可行的手段。分子力学的核心是分子力场。本文介绍了分子力场的量子力学背景、分子力场和光谱力场之间的关系。分子力场的一般形式、分力     

Ab initio calculations of the structure and harmonic force fields for the amine forms of dinitramine and methyldinitramine. Vibrational spectra and their interpretation using a scaling procedure

Ab initio geometries and vibrational spectra have been calculated for the amine structures of dinitramine and methyldinitramine, HN(NO₂)₂ and CH₃N(NO₂)₂. It is shown at the RHF and MP2 levels with the use of the 6-31G^* and 6-31G^** basis sets that these molecules have different symmetries in their equilibrium states,C _sandC ₁ respectively. The quantum chemical RHF/6-31G^* force fields were scaled with the set of transferable factors previously obtained by the authors to assign the available experimental vibrational bands and predict the positions of bands for the unmeasured spectral regions. Some common patterns of the geometrical parameters, vibrational spectra, and force fields of the simplest nitramines are discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2135–2147, November, 1995.The authors are grateful to the Russian Foundation for Basic Research (Project No. 93-03-4410) and to the International Science Foundation (Grant No. MQXOOO) for financial support of works fulfilled at the Department of Chemistry, M. V. Lomonosov Moscow State University. The authors also acknowledge the support of the Scientific Technical Program Universities of Russia.     

凝聚相中振动能量弛豫的理论研究

凝聚相中的振动能量弛豫是化学、物理学和生物学中一个非常重要的动力学过程.近年来, 许多实验和理论方法业已建立并用来探索它的微观机理.本文简要介绍一些常用理论方法及其应用,并对将来的发展方向作一展望.     

Vibrational spectra of dihalonitromethanes. 1. Dichloro-, difluoro-, and fluorochloronitromethanes

Conclusions Based on an analysis of the vibrational spectra of dihalodinitromethanes, it was shown that the conformation in which the NO and CH bonds are screened is predominant for dihalodinitromethanes.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2523–2530, November, 1988.     

Vibrational spectra of difluoromethanimine CF2NH calculated from an ab initio CI quartic force field

Some energy levels up to 3500 cm⁻¹ above the zero point energy have been calculated for difluoromethanimine CF₂NH and its deuterated isotopmer CF₂ND from a complete quartic force field computed at MP2/6-311G^** level of theory. The results show a very good agreement with the most reliable fundamental experimental values, the mean deviations being found to be 5 and 6 cm⁻¹ for the two molecules studied. Our complete quartic force field predicts or confirms the assignment of some overtones and combination bands in the medium IR region.