Experimental and theoretical vibrational study of 2,2,2-trifluoroethyl trifluoromethanesulfonate, CF3SO2OCH2CF3

The infrared spectra of 2,2,2-trifluoroethyl trifluoromethanesulfonate (CF3SO2OCH2CF3) were obtained in the gaseous, liquid and solid states as well as the Raman spectrum of the liquid. Quantum chemistry calculations using the density functional theory were used to predict the most stable geometry and conformation of the studied molecule. Subsequently, the harmonic vibrational frequencies and force field were calculated. An assignment of the observed spectral features made after comparison with the related molecules and with the predicted frequencies was used as the basis of a scaling of the original force field in order to reproduce as well as possible the experimental frequencies. With this purpose a set of scale factors was calculated by a least square procedure, leading to a final root mean square deviation (RMSD) of 9.7 cm(-1).     

Theoretical structure and vibrational analysis of ethyl methanesulfonate, CH3SO2OCH2CH3

Ethyl methanesulfonate, CH3SO2OCH2CH3, is well-known as an alkylating agent in mutagenic and carcinogenic processes. Its electronic structure and that of the methanesulfonate anion (CH3SO3-) were determined using optimization methods based on density functional theory and Moller-Plesset second-order perturbation theory. For CH3SO2OCH2CH3, two conformations with symmetries C(s) and C1 are obtained, the former being more stable than the latter. Natural bond orbital (NBO) calculations show the C(s) conformation provides a more favorable geometry of the lone pairs of the oxygen atom linking the ethyl group. The NBO technique also reveals the characteristics of the methanesulfonate anion as a leaving group due to the rearrangement of the excess electronic charge after alkylation. Furthermore, the infrared spectra of CH3SO2OCH2CH3 are reported for the liquid and solid states as well as the Raman spectrum of the liquid. Comparison to experiment of the conformationally averaged IR spectrum of C(s) and C1 provides evidence of the predicted conformations in the solid IR spectrum. These experimental data along with the calculated theoretical force constants are used to define a scaled quantum mechanical force field for the target molecule, which allowed the measured frequencies to be reproduced with a final root-mean-square deviation of 9 cm(-1) and, thus, a reliable assignment of the vibrational spectrum.     

Skeleton Vibrations and Force Constants of ［Fe_2Cr（μ_3－O）（glycine）_6（H_2O）_3］（NO_3）_7．3H_2O

ＳｋｅｌｅｔｏｎＶｉｂｒａｔｉｏｎｓａｎｄＦｏｒｃｅＣｏｎｓｔａｎｔｓｏｆ［Ｆｅ_２Ｃｒ（μ_３－Ｏ）（ｇｌｙｃｉｎｅ）_６（Ｈ_２Ｏ）_３］（ＮＯ_３）_７．３Ｈ_２ＯＺｈａｎｇＬｉｎ－Ｎａ，ＬｉｎＺｈｅｎｇ－Ｙａｎ（ＳｔａｔｅＫｅｙＬａｂｏｒａｔｏｒｙｏ...     

Gas-phase structure, rotational barrier, and vibrational properties of methyl methanethiosulfonate, CH3SO2SCH3: an experimental and computational study

The molecular structure of methyl methanethiosulfonate, CH3SO2SCH3, has been determined in the gas phase from electron-diffraction data supplemented by ab initio (HF, MP2) and density functional theory (DFT) calculations using 6-31G(d), 6-311++G(d,p), and 6-311G(3df,3pd) basis sets. Both experimental and theoretical data indicate that although both anti and gauche conformers are possible by rotating about the S-S bond, the preferred conformation is gauche. The barrier to internal rotation in the CSSC skeleton has been calculated using the RHF/6-31G(d), MP2/6-31G(d), and B3LYP/6-31G(d) methods as well as MP2 with a 6-31G(3df) basis set on sulfur and 6-31G(d) on C, H, and O. A 6-fold decomposition of the rotational barrier has been performed in terms of a Fourier-type expansion, enabling us to analyze the nature of the potential function, showing that the coefficients V1 and V2 are the dominant terms; V1 is associated with nonbonding interactions, and V2 is associated with hyperconjugative interactions. A natural bond orbital analysis showed that the lone pair --> sigma* hyperconjugative interactions favor the gauche conformation. Furthermore, the infrared spectra for the liquid and solid phases and the Raman spectrum for the liquid have been recorded, and the observed bands have been assigned to the vibrational normal modes. The experimental vibrational data, along with calculated theoretical force constants, were used to define a scaled quantum mechanical force field for the target system that enabled us to estimate the measured frequencies with a final root-mean-square deviation of 6 cm-1.     

[Cl_3Sb(μ-S)SbCl_3]~(2-)阴离子的红外光谱和简正坐标分析

在500—100cm~(-1)波段范围内测定了[Cl_3Sb(μ-S)SbCl_3]~(2-)阴离子的Fourier变换红外光谱。采用简化的普遍价力场(SGVFF)进行了简正坐标分析,振动基频的计算值与观测值符合良好,两者平均偏差小于1.0％,证实了振动谱带的归属,确定了相应的力常数。最后讨论了谱带归属问题和所得结果的合理性和可靠性。     

Au2、Au3小团族分子的结构和势能函数

原子团簇的结构和性质研究是当今物理学和材料学中的一个热门课题,过渡金属团簇特别是Au团簇,由于其独特的物理和化学性质而被广泛地应用于催化反应、材料吸附[1-2]和光的吸收中[3]。近年来,人们用不同的理论方法研究金原子团簇。H儯kkinen等人利用GGA方法研究了中性和阴离Au2-10团簇的性质[4];Bravo-P啨rez等人采用从头计算的HF和post-HF方法研究Au2-Au6小团簇[5],这些计算结果与实验值相比,相差较大。由于金团簇电子结构的复杂性,对Au体系考虑旋—轨耦合和电子相关效应是很重要的,这种计算的不确定性对Au的影响比IB簇的其它金属团…     

Infrared and Raman spectra and theoretical study of methyl trifluoromethyl sulfone, CF3SO2CH3

The infrared and Raman spectra were obtained for liquid CF3SO2CH3, as well as the infrared spectrum of the gaseous substance. The molecular geometry was optimized by means of the Hartree-Fock (HF), second order electron correlation (MP2) and density functional theory (DFT) procedures of quantum chemistry, resulting in a structure with Cs symmetry. The wavenumbers corresponding to the normal modes of vibration were calculated using the DFT (B3LYP/6-31G**) approximation and their agreement with the measured values improved after scaling of the associated force field. An assignment of bands is proposed on the basis of such calculations and the comparison with related molecules.     

Molecular structure and conformation of gaseous 2-chloro-3-fluoro-1-propene

2-Chloro-3-fluoro-1-propene has been studied by electron diffraction, and the molecule was found to exist in equilibrium between a syn and a gauche conformation, with the syn conformation as the most stable. The most important structure parameters with standard deviation are: r_g(CC) = 1.338(6) Å,r_g(C—C) = 1.505(5) Å, r_g(C—F) = 1.378(4) Å, r_g(C-Cl) = 1.743(3) Å, ∠CC—Cl = 123.0(7)°, ∠CC—C = 125.6(6)° and ∠C—C—F = 111.2(8)°.A force field was determined by a least-squares refinement to vibrational frequencies. Mean square amplitudes of vibration and perpendicular amplitude correction coefficients have been calculated. The mean square amplitudes of vibration from the electron diffraction data are in very good agreement with the values calculated from the spectroscopic data.     

Electronic Structure and Properties of Trihalogen Cations X(3)(+) and XY(2)(+) (X, Y = F, Cl, Br, I)

Electronic structures, charge distributions, geometries, valence force constants, and vibrational frequencies of the homoatomic clusters F(3)(+), Cl(3)(+), Br(3)(+), and I(3)(+) and of the heteroatomic clusters ClF(2)(+), BrF(2)(+), IF(2)(+), BrCl(2)(+), ICl(2)(+), and IBr(2)(+) were determined. The self-consistent field approach extended by MP2-correlation energy or density-functional corrections was applied using various basis sets. It was found that d- and f-type polarization functions play a crucial role as in some other halogen compounds. The MP2 approach yields the most satisfactory results. The effect of the crystalline environment surrounding the Cl(3)(+), Br(3)(+), and I(3)(+) species is successfully simulated by a Madelung potential. Frequencies calculated in the crystal field are in reasonable agreement with the more reliable ones among the experimental results. Coupling force constants were determined. They are not consistent with some empirical rules. Bonding and charge distributions of the formally mixed-valence systems X(+)Y(2)(0) are discussed. X(+) behaves like a divalent chalcogen with high electronegativity. Each of the X(+)-Y bonds in XY(2)(+) is very similar to the bond in X-Y. We predict the experimentally unknown F(3)(+) to be stable in vacuum but not in the solid state. Structures and frequencies of XY(2)(+) species, which are as yet unknown, are also predicted.     

[Cl2FeS2MoS2FeCl2]^2^-阴离子的FT-IR光谱和简正坐标分析

在500-100cm^-^1波段范围内测定了[Cl2FeS2MoS2FeCl2]^2^-簇阴离子的Fourier变换红外光谱.采用简化的普遍价力场(SGVFF)进行了简正坐标分析.振动基频的计算值与观测值符合良好,两者平均偏差小于1.0%证实了振动谱带的归属;确定了包括伸缩、变角、扭曲以及伸缩-伸缩相互作用的16个力常数.最后还讨论了所得结果的合理性和可靠性.     

Vibrational spectrum of 3-methyl and 4-methylpyridine

The assignments of the vibrational spectra of the 3-methyl and 4-methylpyridine molecules have been carried out following the SQMFF methodology (scaled quantum mechanical force field). The theoretical frequencies have been obtained by calculating the RHF/3-21G force field, using the scale factors for pyridine and 2-methylpyridine and are correlated in a satisfactory manner with the frequencies recorded in the IR and Raman of these methyl derivatives.     

Density functional theory studies on tautomeric stability and infrared spectra of 2-chloroadenine

The tautomeric stability and vibrational IR spectrum of 2-chloroadenine were studied using density functional theory (DFT) at B3LYP/6-31G* level. The amino N(9)H tautomer of 2-chloroadenine was predicted to be most stable. A scaled quantum mechanical (SQM) force field approach was used to calculate the vibrational frequencies of amino N(9)H form of 2-chloroadenine. The force constant scale factors were transferred from those of purine. The mean deviation between the predicted vibrational frequencies and the observed ones is 8.0 cm(-1). The results made it possible to give complete assignments of the IR spectrum of this molecule.     

Ab initio and molecular mechanics (MM2 and MM3) calculations of positively charged conjugated nitrogen-containing compounds

Ab initio calculations have been carried out on s-trans-N-vinylmethyleneammonium, pyridinium, and related compounds to obtain rotational barriers, structures, and vibrational frequencies. The restricted Hartree-Fock (RHF) level of theory with 6-31G** basis set was used for these calculations. In addition, the MM2(91) and MM3(94) force fields have been parameterized to calculate these positively charged nitrogen-containing compounds. A bond order term was incorporated in the force field to reproduce accurately the rotational barriers of s-trans-N-vinylmethyleneammonium and related compounds. Molecular mechanics geometries and vibrational frequencies compare well with those calculated by ab initio methods. © 1996 by John Wiley & Sons, Inc.     

Cis- and trans-3-hexene: infrared spectrum in liquid argon solution, ab initio calculations of equilibrium geometry, normal coordinate analysis, and vibrational assignments

The infrared spectra of cis-3-hexene and trans-3-hexene dissolved in liquid argon have been obtained at temperatures from 93 to 120 K. The absorptions were observed with a low-temperature cell and a Fourier transform infrared spectrophotometer. Ab initio molecular orbital calculations were performed to obtain the equilibrium geometry, vibrational frequencies, force fields, and infrared intensities. The calculations were done at the Hartree-Fock level using 6-31G basis set. The Cartesian force fields from ab initio calculations have been converted to the force field in symmetry coordinates. The scale factors of ab initio calculated force fields were determined. Normal coordinate calculations were performed using a scaled quantum mechanical (SQM) force field. Vibrational normal modes calculated for the lowest energy rotamers of cis- and trans-3-hexene have been assigned to infrared absorption bands observed in liquid argon solution. The assignments were based on calculated frequencies and potential energy distributions. The equilibrium geometries of the two lowest energy rotamers (symmetry C₂ and C_s) of cis-3-hexene and of the three lowest energy rotamers (symmetry C_i, C₂, and C₁) of trans-3-hexene were calculated. Variable temperature studies of the infrared spectrum of cis- and trans-3-hexenes dissolved in liquid argon were done to obtain the ΔH of conversion between the rotamers C₂ and C_s of cis-3-hexene and between the rotamers C_i, C₂, and C₁ of trans-3-hexene.     

The structure, Raman spectra, and force fields of methylbromosilanes CH3SiClnBr3−n (n = 0, 1, 2)

The laser-excited Raman spectra of liquid CH₃SiCl_nBr_3?n (n = 0, 1, 2) were studied. Quantumchemical calculations of these substances with geometry optimization were performed to determine their harmonic force fields and vibrational frequencies. The calculations were made using the HF/6-31G* and HF/6-311++G** approximations and density functional theory at the B3LYP/6-31G* and B3LYP/6-311++G** levels. An interpretation of the spectra was suggested and the calculated force fields were discussed in comparison with the data on related compounds.     

Vibrational anharmonicity and harmonic force fields for dichloromethane from quantum-chemical calculations

Anharmonic and related constants have been calculated for CH2Cl2, CD2Cl2, and CHDCl2 by using the program Gaussian03 and B3LYP and MP2 models. Bases used were 6-311++G** and cc-pVTZ. The size of grid used in the B3LYP/6-311++G** model had a noticeable effect on resulting data. Features of the MP2/6-311++G** calculations suggested a deleterious effect of the absence of f functions in this basis set. The need for the replacement of second-order terms in the perturbation theory formulas for the vibrational anharmonic constants x ij in the presence of Fermi resonance was explored, and minor resonances were found associated with the cubic constants varphi 122 and varphi 299 (d 0 isotopomer), phi122 and phi849 (d2), and phi278 (d1). Computed xij values for nuCH and nuCD motions agree quite well with earlier experimental data. Observed anharmonic frequencies, nu obsd, were corrected to "observed" harmonic frequencies, omega obsd, by using computed differences Delta = omegaQC-nuQC. These differences Delta are larger for the antisymmetric nuasCH2 mode than for symmetric nusCH2 motion. This fact made it necessary to use differing scale factors for the two kinds of CH stretching force constants in a subsequent scaling of the harmonic force field to nuobsd. Force field scaling was also carried out by refining to omega obsd. In both approaches, the B3LYP models required differing scale factors for symmetric and antisymmetric CCl stretching force constants, indicating a failure to compute an accurate C-Cl stretch-stretch interaction force constant. The MP2/cc-pVTZ force field was preferred. Both scaled and unscaled harmonic force fields were used to calculate centrifugal distortion constants (CDCs) and contributions to the vibrational dependence of the rotational constants (alphas). Variations in the CDCs can, in part, be explained by the magnitudes of the frequencies used in the scaling process.     

A theoretical study of vibrational spectra of tetranitrate-methyl-β-D-glucopyranoside and 2,3-di-O-nitro-methyl-β-D-glucopyranoside

Coupled calculations were carried out of normal vibration frequencies from the point of view of the valence-force field scheme and of absolute IR band intensities by the CNDO/2 method for the tetranitrate-methyl-β-D-glucopyranoside molecule. A good agreement was achieved with the experiments. Normal coordinate analysis was made for 2,3-di-O-nitro-methyl-β-D-glucopyranoside molecule with force constants obtained for the tetra-nitrate-methyl-β-D-glucopyranoside. Before proceeding to the calculation of the spectra of such complex molecules of nitrates of monosaccharides, a complete experimental and theoretical investigation was performed of the vibrational spectra of methylnitrate, which made it possible to determine the deficit of force constants for the calculations of the spectra of nitrosubstituted glucopyranosides. Detailed interpretations of the observable IR spectra of both the nitro-glucopyranosides compounds considered are given. The absorption spectra sensitivity to the spot of the nitrate group localization was discovered. Special attention was focused on analyzing the spectra of nitrates of saccharides for the characteristic split of the band due to the asymmetric stretching vibrations of the ONO₂ groups in the region of 1600–1700 cm⁻¹.     

Vibrational analysis of tertiary alkyl chlorides

Vibrational spectra were obtained for 2-chloro-2-methylpentane, 3-chloro-3-methylpentane, 2-chloro-2-methylhexane, and 3-chloro-3-methylhexane. All four compounds exist in T_HHH and T_CHH conformations in the neat liquid, and the T_HHH' conformer of the last named compound also seems to be present. Only the T_HHH conformer is present in the crystalline state of the two pentanes, but the hexanes could not be made to crystallize and both conformers were present in the solid. A 44-parameter modified valence force field was used in normal coordinate calculations, with fifteen force constants being adjusted to fit 188 assigned frequencies below 1500 cm^?1 of six molecules (two conformers each of 2-chloro-2-methylbutane, 2-chloro-2-methylpentane, and 3-chloro-3-methylpentane). The resulting force constant values were used in zero-order calculations of the two hexanes as an aid in interpreting vibrational spectra for those compounds.     

2-氟-5-溴吡啶分子振动光谱的密度泛涵理论研究

用密度泛函理论方法B3LYP以及6-311++G(2df,2pd)基组对2-氟-5-溴吡啶分子 的平衡几何构型进行了优化并计算了该分子的振动谐力场。使用Pulay的标度方法 对理论力场进行了标度。采用Wilson的GF矩阵方法,根据标度后的理论力场进行了 简正坐标分析,对2-氟-5-溴吡啶分子的振动基频进行了理论研究,得到了势能分 布和红外振动频率。与红外频率的实验值相比较,理论频率的均方差为24 cm~(-1) 。此外,根据振动模式的势能分布对此分子的振动基频进行了理论归属,并对前人 的指认进行了修正和补充。     

Conformations and vibrational spectra of 2-chloro-3-fluoro-1-propene and 2-bromo-3-fluoro-1-propene

The infrared spectra of 2-chloro-3-fluoro- and 2-bromo-3-fluoro-1-propene as vapours and liquids were recorded in the region 4000–4050 cm^?1. Additional spectra of the amorphous and crystalline solids at ?170 °C and of the liquids in polar and non-polar solvents were recorded between 4000 and 200 cm^?1.Raman spectra, including semi-quantitative polarization measurements of the liquids were obtained. Spectra were also recorded with the samples dissolved in polar and non-polar solvents, and unannealed as well as annealed crystalline solids were studied at ?180 °C.Approximately 14 vibrational bands present in the spectra of the liquids, solutions and the glassy solids vanished in the infrared and Raman spectra of the crystals. From various criteria it can be concluded with certainty that the more polar (gauche) and less polar (cis) conformers were present in the crystalline chloro- and bromo- compounds, respectively. From infrared and Raman band intensities it was estimated that the conformational equilibrium in chlorofluoro-propene was highly displaced towards cis in the vapour, with both conformers approximately equally abundant in the liquid state (30 °C). For bromofluoro- propene the equilibrium was still further displaced towards the cis conformer.A striking similarity between the spectra of the two compounds was ob- served. The fundamental frequencies have been tentatively assigned and checked by force constant calculations. Dipole moments and relative stabilities of the conformers were estimated by a CNDO calculation.