IR and Raman Spectra

FT-IR and FT-Raman spectroscopies combined with DFT quantum chemical calculations have been used to probe the fundamental modes of vibrations of many thiophene-containing molecules. The majority of work in this field was performed by Casado, Herndndez, Ldpez Navarrete and co-workers. 

Great resemblance was found between the B3LYP/3-21G infrared spectrum of BMA-IT and the experimental spectrum [85]. The actual Raman spectral pattern was nicely reproduced, both in peak positions 

Four ring-stretching modes for pyridines and pyrimidines are listed in Table 20, together with the corresponding bands of a monosubstituted benzene. Quinolines and isoquinolines show seven or eight bands in the region 1650-1350 cm-1. 

In six-membered aromatic rings the intensity of the ring-stretching mode near 1600 cm 1 is related to the square of the ctr° parameter for the substituent and/or ring atoms. Such intensity measurements on 4-substituted pyridine A-oxides confirm the ability of the A-oxide group to both donate and withdraw electrons according to the nature of the 4-substituent. 

Six-membered heteroaromatic rings show bands characteristic of in-plane CH bending in the region 1300-1000 cm1 (Table 21), and of out-of-plane CH bending below 1000 cm 1 (Table 22). 

The position of the carbonyl group in the IR spectra of various pyranones and pyridones, etc., is indicative of the C-0 bond order, and therefore of the importance of the betaine structure. However, this criterion must be used with caution because of the non-localized nature of the vibrations just mentioned. 

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Chlorine Pentafluoride. Chlorine pentafluoride is a colorless gas at room temperature. The ir and Raman spectra of the Hquid and gas phase have been studied (34,39). The uv absorption spectmm (45) and vapor pressure data may be found in the Hterature (18). 

Iodine Pentafluoride. Iodine pentafluoride is a straw-colored Hquid the ir and Raman spectra of the gas phase have been studied (19,46,47) vapor pressure data are given in References 14 and 48. 

Selected physical properties are given ia Table 4. The nmr data (97) and ir and Raman spectra (98) have also been determined. Thermodynamic functions have been calculated from spectral data (99). 

Triphenylbismuth oxide [7173-99-1/, C gH BiO, has been prepared from triphenylbismuth dicyanide [41083-16-3], C2QH25B1N2, and mercuric oxide (151), and from triphenylbismuth dichloride and moist silver oxide (152). The ir and Raman spectra of this compound suggest that it is polymeric and has Bi—O—Bi bonds (153). Triphenylbismuth dihydroxide, and triarylbismuth hydroxide haUdes, eg, triphenylbismuth hydroxide chloride... 

Most of the bands in the IR and Raman spectra of unsubstituted pyrimidine can be assigned to the vibrations of the nucleus (57SA113) and the spectra of its cation are rather similar (60JCS1226, 60JCS1232) salient points have been discussed (62HC(16)477>. Similar... 

The IR (and Raman) spectra of 1,2-benzisoxazole and 2,1-benzisoxazole have been recorded and their fundamental and combined vibrations assigned (80MI41604). Similar studies have been carried out with 2,1-benzisoxazolium salts (74DIS(B)147, 71JOC1543). 

State or vibrational energies. If the current across the metal-insulator-metal sandwich is recorded as a function of applied voltage, the current increases as the threshold for each state or vibrational mode is crossed. The increases in current are in fact very small, and for improved detectability the current is double-differentiated with respect to voltage, thereby providing, in effect, a vibrational spectrum that can be compared directly with free-molecule IR and Raman spectra. 

The technique of N-enrichment has been used in several cases to distinguish S-N from S-S vibrations. The IR and Raman spectra of... 

To predict the IR and Raman spectra of molecules (frequencies and intensities). 

We ve included several papers in the References section which perform theoretical and experimental studies of the IR and Raman spectra for these compounds. These compounds were among the earliest ab initio frequency studies of such systems. In addition, in the case of propellane, theoretical predictions of its energy and structure preceded its synthesis. 

Atomic charges and electrostatic potentials Vibrational frequencies IR and Raman spectra NMR properties... 

In addition to the obvious structural information, vibrational spectra can also be obtained from both semi-empirical and ab initio calculations. Computer-generated IR and Raman spectra from ab initio calculations have already proved useful in the analysis of chloroaluminate ionic liquids [19]. Other useful information derived from quantum mechanical calculations include and chemical shifts, quadru-pole coupling constants, thermochemical properties, electron densities, bond energies, ionization potentials and electron affinities. As semiempirical and ab initio methods are improved over time, it is likely that investigators will come to consider theoretical calculations to be a routine procedure. 

The complexes of aromatic hydroxy carboxylic acids (salicylic acid and its isomers) with [Bu2Sn(IV)] and [Ph3Sn(IV)] were obtained. The FT-IR and Raman spectra clearly demonstrated that the organotin(IV) moieties react with the O, O) atoms of the ligands. It was found that in most cases the -COO group chelated to the central atoms, but monodentate coordination was also observed. The complexes probably have polymeric structures. 

IR and Raman spectra of the NbS2X2 compounds have been measured, and assigned to the different modes (271). Especially in the absence of X-ray data, such measurements serve to prove the presence of S-S and Nb-S modes (see Table X). Magnetic data are available for... 

The Aldrich Library of Infrared Spectra , 3rd ed., Aldrich chemical Company, Milwaukee, WI, 1981, by Pouchert contains more than 12,000 IR spectra so arranged that the user can readily see the change that takes place in a given spectrum when a slight change is made in the structure of a molecule. The same company also publishes the Aldrich Library of FT-IR Spectra and the Aldrich Library of NMR Spectra , both also by Pouchert. A similar volume, which has ir and Raman spectra of about 1000 compounds, is Raman/Infrared Atlas of Organic Compounds , 2nd ed., VCH, New York, 1989, by Schrader. 

Matrix IR and Raman spectra of tetramethyldigermethene, Mc2Ge=GeMe2, which was obtained by pyrolysis (140-200°C) of compound [154], have been recorded (Bleckmann et al., 1984). Since this intermediate... 

A group of investigators recently suggested that the density-functional theory (DFT), which calculates IR and Raman spectra, is a useful tool for direct characterization of the structures of diamondoids with increasing complexity [66]. They applied DFT to calculate Raman spectra whose frequencies and relative intensities were shown to be in excellent agreement with the experimental Raman spectra for C26H30, thus providing direct vibrational proof of its existence. 

The well-known tetrahedral [Co(NCS)4]2 ion has continued to attract attention from analytical chemists, physical chemists, and spectroscopists. The inelastic electron tunneling (IET) spectrum of (Me4N)2[Co(NCS)4] was compared with IR and Raman spectra of the same complex.359 The vibrational bands due to the Me4N+ were prominent in all three spectra, but Coligand stretches were absent from the IET spectra. The lowest 4 42 4T2 electronic transition was strong in the IET spectrum but absent from the IR spectrum. The electric dipole allowed 4A2 4TX electronic transition was observed in both the IET and IR spectra and no fine structure was observed. Complex formation equilibria between Co11 and SCN- were studied calorimetri-... 

In order to co clarify the role of complex formation, the new data on stability constants should be accumulated, being collected at strictly similar conditions. It should be also mentioned that any analysis of equilibrium in solutions involving anions of polybasic hydroxy carboxylic acids requires the data on the deprotonation constants of the acid in question. This information would be crucial for conclusions regarding the presence and stability of mixed complexes in the system. Valuable knowledge about the structure of complex compounds present in solutions (and in precursors as well, see later) may be gained by means of vibrational spectroscopy (IR and Raman spectra) and nuclear magnetic resonance. 

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