Conformation and vibrational spectra of 1,5-hexadiyne (bipropargyl) and 1,5-hexadiyne-1,6-d2

The infrared spectra of 1,5-hexadiyne (bipropargyl) and 1,5-hexadiyne-1,6-d₂ as vapours, liquids, as solutes in various solvents and as crystalline solids at low temperatures and at high pressures have been recorded. Raman spectra were obtained for the liquids, including semiquantitative polarization measurements, and for the low temperature crystals.The data were interpreted in terms of two conformers, anti and gauche, in the vapour and liquid state and one, the anti, in the crystalline forms. A phase transition for 1,5-hexadiyne was observed at ca. 240 K. Both the high and low temperature crystals had molecules in the anti conformer.Interpretation of the spectra in terms of conformational equilibria was facilitated by a thorough vapour phase band contour analysis. With a few exceptions, all the vibrational fundamentals for both conformers were assigned and found to be in good agreement with results from normal coordinate calculations.     

Conformation and vibrational spectra of 1-bromo-1,5-hexadiyne (bromobipropargyl)

The IR spectra of 1-bromo-1,5-hexadiyne (bromobipropargyl) as a vapour, liquid and crystalline solid and in several solvents have been recorded. Raman spectra were obtained for the liquid (including polarization measurements) and the crystal.The data were interpreted in terms of two conformers, trans and gauche, in the vapour and liquid states and one, trans, in the crystal. The conclusion that the trans conformer was the one present in the crystal was based on several independent pieces of evidence. Vibrational assignments were made, supported by normal coordinate calculations.     

The conformation and vibrational spectra of 1,5-hexadiene-3-yne (divinylacetylene) and perchloro-1,5-hexadiene-3-yne (perchlorodivinylacetylene)

Infrared spectra of 1,5-hexadiene-S-yne (divinylacetylene) have been recorded in the vapour phase, in solution and in the amorphous and crystalline solid states at 90 K in the region 4000–4020 cm^?1. Correspondingly, IR spectra ofperchloro-1,5-hexadiene-3-yne (perchlorodivinylacetylene) as a melt, as a solute in various solvents and as a solid at 90 K have been obtained. Raman spectra of the two compounds were recorded in the liquid (molten) state including polarization measurements, and as crystalline solids at 90 K.The spectral data indicate that each compound exists as one conformer only in the various states of aggregation. In divinylacetylene the molecular symmetry appears to be anti (C_2h) while for perchlorodivinylacetylene the symmetry is either C_2v (syn) or C₂ (gauche). Vibrational assignments for the spectra of both molecules are presented and the values are compared with the results of normal coordinate analyses.     

Conformation-specific spectroscopy of 3-benzyl-1,5-hexadiyne

3-Benzyl-1,5-hexadiyne (BHD) was studied by a combination of methods, including resonance-enhanced-two-photon ionization, UV-UV hole-burning spectroscopy, resonant ion-dip infrared spectroscopy, and rotational band contour analysis. There are five conformations of BHD observed in the expansion with their 1<-- S0 origins occurring at 37520, 37565, 37599, 37605, and 37631 cm(-1). DFT calculations predict six low energy conformations. Conformational assignments have been made by comparison of the experimental infrared spectra in the alkyl and acetylenic CH stretch region to DFT vibrational frequency and infrared intensity calculations. Rotational band contours provided further confirmation of these assignments. The electronic origin shifts of BHD compare favorably to the electronic origin shifts of 5-phenyl-1-pentyne with the exception of one conformation. This conformation is unique in that it is the only structure with both acetylenic groups in the gauche position over the ring. This gauche-gauche conformation exhibits a perpendicular (b-type) transition and produces extensive vibronic coupling reminiscent of symmetric monosubstituted benzenes.     

Theoretical calculation of the OH vibrational overtone spectra of 1,5-pentanediol and 1,6-hexanediol

It is well-known that intramolecular hydrogen bonding affects the relative energetics of conformers, as well as the OH stretching peak positions, intensities, and width. In this study we simulated the Δv(OH) = 3, 4 overtone spectra of 1,5-pentanediol (PeD) and 1,6-hexanediol (HD) using the peak positions, intensities, and width calculated from the B3LYP/6-31+G(d,p) method. Furthermore, room temperature free energy calculations were performed using B3LYP/6-31+G(d,p) MP2/6-31+G(d,p), and MP2/6-311++G(3df,3pd) to obtain the relative population of the conformers. From the calculation of 109 and 381 distinct conformers for PeD and HD, respectively, we find that for these long chain diols the intramolecular hydrogen bonded conformers are not the most dominant conformation at room temperature. This is in stark contrast with shorter chain diols such as ethylene glycol for which the hydrogen bonded conformer dominates the population at room temperature. On the other hand, we found that the correlation between the hydrogen bonded OH red shift versus the homogeneous width, Γ = 0.0155(Δω)(1.36), which was derived for shorter chain diols, is valid even for these longer chain diols. We also showed that the intramolecular hydrogen bonded OH initially decays through the CCOH torsion and COH bending mode no matter how long the alkanediol chain length is for 1,n-alkanediols for n up to 6.     

The vibrational spectra of tetramethylammonium tetrafluoro- and tetrachloro-dimethylantimonates(V)

The low-frequency i.r. and Raman spectra of solid Me₄N[Me₂SbF₄] and Me₄[Me₂SbCl₄], and the Raman data in MeCN solution are reported and assigned. Spectral data are in accordance with the presence of trans-Me₂SbX₄⁻ octahedral species having D_4h skeletal symmetry.     

Ab initio calculations on the isomerization of the 1,5-hexadiyne radical cation

Ab initio calculations at the MRCI//ROHF/6-31G** level suggest that the 1,5-hexadiyne radical cation is not stable and isomerizes to the 1,2,4,5-hexatetraene radical cation without a barrier. After this rearrangement, the internal energy of the ions will be sufficient for a subsequent isomerization to the benzene structure. At energies of about 1 eV above the vertical ionization energy, the 1,5-hexadiyne radical cation may dissociate to linear neutral and ionic C₃H₃ fragments. These results are in excellent agreement with previous experiments.     

Theoretical prediction of vibrational spectra. The a priori scaled quantum mechanical (SQM) force field and vibrational spectra of pyrimidine

The complete harmonic force field of pyrimidine has been computed at the ab initio Hartree—Fock level using a 4–21 Gaussian basis set. In order to compensate the systematic overestimations of the force constants at the aforementioned level of quantum mechanical approximation, the theoretical force constants were empirically scaled by using nine scale factors. (The values of all these scale factors were previously determined by fitting the theoretical force field of benzene to the observed vibrational spectra of benzene.) The resulting a priori scaled quantum mechanical (SQM) force field is regarded as the most accurate and physically the most correct harmonic force field for pyrimidine. This force field was then used to predict the vibrational spectra of pyrimidine-h₄ and pyrimidine-d₄. On the basis of these a priori vibrational spectra uncertain assignments have been confidently resolved. After a few reassignments, the mean deviations between the experimental and calculated frequencies are below 9 and 18 cm⁻¹ for the non-CH stretching in-plane and the out-of-plane vibrations, respectively. Computed IR intensities are generally in agreement with experiments at a qualitative level.     

Structure and vibrational spectra of copper(II) 2-pyridylmethanolate tetrahydrate

In the memory of Prof. Ing. Ladislav Valko, DrSc. (1930–2013) A room-temperature synthesis of copper(II) 2-pyridylmethanolate tetrahydrate, [CuL₂] · 4H₂O, with nearly quantitative yields with its structure redetermined at 213 K is presented. In agreement with the X-ray structure data, the DFT quantum-chemical calculations confirmed the planar structure of CuL₂ (C _2h symmetry). The measured IR and Raman spectra were interpreted using the DFT calculations and some erroneous assignments in the previous studies have been corrected.     

The solid state vibrational spectra of pentacarbonyl-pyridine-molybdenum(0) complexes

The solid state i.r. and Raman spectra are presented for a number of Mo(o) compounds of the type Mo(CO)₅X (X: pyridine derivatives). The νCO, δMoCO, νMoC and νMoN fundamentals are assigned considering a C_4ν symmetry and the complete vibrational analysis is given for the pyridine and the pyridine-d₅ complexes. A linear relation between the lowest Raman νCO mode and the νMoN has been observed.     

DFT oligomer approach to vibrational spectra of poly(p-phenylenevinylene)

Experimental Raman and infrared spectra of poly(p-phenylenevinylene) have been analyzed on the basis of the normal coordinate calculations based on the density functional theory method at the B3LYP/cc-pVDZ level for a model oligomer. Vibrational modes corresponding to optically active modes of an infinite polymer chain have been selected from the calculated results. On the basis of these normal vibrations, the observed vibrational spectra of poly(p-phenylenevinylene) have been explained successfully. The angles between the calculated transition dipole moment vectors and the polymer axis for some infrared bands agree with those derived from observed infrared dichroic spectrum.     

The vibrational spectra of the trimethyl-and triphenyl-antimony(V) dihalides

The complete i.r. and Raman spectra for the series (CH₃)₃SbX₂ and (C₆H₅)₃SbX₂ (where X = F, Cl, Br, I) are reported. The vibrational assignments are made and discussed.     

FC(O)NCS 分子振动光谱的理论研究

采用DFT(B3LYP)方法,以6-3G*为基组对FC(O)NCS的顺式和反式两种构型的几何结构,振动谐性力场和红外光谱进行了研究。B3LYP/6-31G*计算水平和大多数有机分子的一套固定标度因子进行标度。根据标度后的理论力场进行简正坐标分析得到的势能分布(PED)和红外光谱强度值对FC(O)NCS分子的顺式和反式两种构型的振动基频进行了理论归属。     

Nuclear resonance vibrational spectra of five-coordinate imidazole-ligated iron(II) porphyrinates

Nuclear resonance vibrational spectra have been obtained for six five-coordinate imidazole-ligated iron(II) porphyrinates, [Fe(Por)(L)] (Por = tetraphenylporphyrinate, octaethylporphyrinate, tetratolylporphyrinate, or protoporphyrinate IX and L = 2-methylimidazole or 1,2-dimethylimidazole). Measurements have been made on both powder and oriented crystal samples. The spectra are dominated by strong signals around 200-300 cm(-1). Although the in-plane and out-of-plane vibrations are seriously overlapped, oriented crystal spectra allow their deconvolution. Thus, oriented crystal experimental data, along with density functional theory (DFT) calculations, enable the assignment of key vibrations in the spectra. Molecular dynamics are also discussed. The nature of the Fe-N(Im) vibrations has been elaborated further than was possible from resonance Raman studies. Our study suggests that the Fe motions are coupled with the porphyrin core and peripheral groups motions. Both peripheral groups and their conformations have significant influence on the vibrational spectra (position and shape).     

Syntheses and vibrational spectra of xenon(VI) fluorozirconate(IV) and xenon(VI) fluorohafnate(IV)

Liquid xenon difluoride at 140°C does not react with zirconium or hafnium tetrafluorides, neither does liquid xenon hexafluoride at 60°C. Therefore reactions between the corresponding hydrazinium fluorometalates or ammonium fluorometalates and xenon difluoride and xenon hexafluoride, respectively, were carried out. N₂H₆ZrF₆ and N₂H₆HfF₆ react with xenon difluoride at 60°C again yielding only the corresponding tetrafluorides, while the analogous reaction with (NH₄)₂ZrF₆ and (NH₄)₂HfF₆ proceeds at 170°C yielding the corresponding ammonium pentafluorometalates, which are stable and do not react further with excessive xenon difluoride up to 200°C.The reaction between N₂H₆ZrF₆ or N₂H₆HfF₆ and xenon hexafluoride proceeds at room temperature yielding a series of thermally unstable compounds of the type mXeF₆.MF₄ (M = Zr, Hf) where m ? 6. The final products which are stable at room temperature are XeF₆.MF₄ (M = Zr,Hf). Spectroscopic evidence suggests that these compounds are salts of a XeF⁺₅ cation squashed between a polymeric anion of the type (MF₅)^x-_x.