IR Studies of Coordinatively Unsaturated Surface Compounds on Silica Gel. IV. CO Complexes of Chromium(II) and Chromium(III)

Three different chromium(II) surface compounds have been identified by their IR spectra of adsorbed CO. Especially important in the interpretation of the experiments are the bands between 2050 and 2035 cm^?1 and the relative intensities of the CO bands at 2100 and 2120 cm^?1. The bands between 2192 and 2179 cm^?1 show also a different pattern for each of the different chromium(II) surface compounds. Two chromium(III) surface compounds could be identified by the presence of either one CO band near 2200 cm^?1 or two bands near 2206 and 2196 cm^?1. Three models are proposed for the chromium(II) title compounds, all related to dinuclear chromium(II) surface complexes: Models one and two have chromium(II) ions with trans and cis configuration in different combinations, respectively, and the third model has a bridging oxygen ion from a siloxan group as a distorting ligand. The three models explain the CO absorptions sufficiently and one is nearly quantitatively in agreement with previous volumetric adsorption studies of CO on chromium(II), which showed the surprising effect of decreasing CO adsorption with decreasing temperature. Two models for the chromium(III) surface compounds are proposed with either an oxygen double bridge or only one bridging oxygen.     

Some 1-substituted quaternary imidazolium compounds and related polymers: Qualitative and quantitative infrared analysis

It was found that 1-substituted quaternary imidazolium compounds show some characteristic infrared (IR) activity. On quarternization of 1-substituted imidazoles strong absorption bands appeared at about 1150 and 1550 cm^?1 in the IR spectra of these compounds. The band at 1150 cm^?1 was assigned to the position 2 C?H bending mode and the 1550 cm^?1 band was attributed to a ring vibration mode of the quaternary imidazolium compounds. The concentration of the quaternary imidazolium units in a polymer can be determined by measuring the intensity of the absorption bands at 1150 or 1550 cm^?1 in relation to another suitable absorption band of the spectrum.     

IR spectroscopy and photosensitivity of the H2OLi complex trapped in a krypton matrix

The reaction of lithium atoms with water has been studied using infrared matrix isolation spectroscopy. H/D and ⁶Li/⁷Li isotopic substitutions and irradiation effects in both visible and IR regions allow us to identify two kinds of complexes: after deposition a 1-1 species, of charge transfer type, characterized by rather small frequency shifts but strong intensity changes of the water bands: after irradiation either in the near IR or in the visible formation of the LiOH molecule identified by two absorptions below 1000 cm^?1: theLiOH stretching mode around 900 cm^?1 and the bending mode at 257 cm^?1. Vibrational calculations on both frequencies and intensities of these complexes allow us to analyse the charge transfer effect in the 1-1 complex and to conclude that the structure of the LiOH molecule is linear.     

Sulfophthalide cycle cleavage and formation of fluorenyl structures upon poly(diphenylene sulfophthalide) thermolysis

Thermolysis of poly(diphenylene sulfophthalide) (PDSP) in the temperature range from 100 to 500 °C was studied by IR and UV-Vis spectroscopy and thermogravimetric analysis. A series of absorption bands in the IR spectrum of PDSP were assigned on the basis of the theoretical calculations of the IR spectrum of diphenyl sulfophthalide used as a model compound, in particular, ν_as(S=O) = 1352 cm^?1, ν_s(S=O) = 1196 cm^?1, ν(C-O) ～ 920 cm^?1, ν(S-O) = 824 cm^?1, and δ(SO₂) = 576 cm^?1. The sulfophthalide cycle (SPC) in PDSP decomposes at the thermolysis temperatures in a range of 260–400 °C. An analysis of the IR spectra of the thermolyzate and the quantum chemical calculations of the IR spectra of the model compounds confirmed the predominant formation of fluorenyl structures in the thermolyzed polymer. The changes in the UV-Vis spectra observed upon the thermolysis of thin films of PDSP (the hypsochromic shift of the long-wavelength absorption band from 271 to 263 nm and the appearance a shoulder at ～310 nm) and the results of TD-DFT calculations of the UV-Vis spectra of the model compounds are consistent with the hypothesis about the formation of fluorenyl structures. The general scheme of PDSP thermolysis at 260–400 °C was proposed in which the major process is the formation of fluorenyl fragments in macromolecules of the polymer due to the intramolecular ring closure in biradicals formed by the SPC cleavage.     

FTIR studies of polyimides. II. Factors affecting quantitative measurement

Measurement of imidization by IR spectroscopy has frequently been reported to give results that are either insensitive to changes in the latter part of the cure or in conflict with observations by other methods. However, an analysis of imide formation using the 1370 cm^?1 band (C? N stretch) in conjunction with the 1500 cm^?1 aromatic band as an internal standard appears capable of giving precise, internally consistent measurements for the most commonly used polyimide structures, for samples that are measured in transmission. Measurements of imide content in ultrathin films by grazing incidence reflection spectroscopy appear to be at least semiquantitative. © 1993 John Wiley & Sons, Inc.     

Die rotationsisomerie des bicyclopropyls.: II. Die gauche/trans-isomerisierungsenthalpie und-entropie von bicyclopropyl aus ir-intensitäts-messungen. Ein experimenteller test

The determination of the enthalpy ΔH and entropy ΔS of the isomerization bicyclopropy l(trans)? bicyclopropyl(gauche) in the liquid phase by the IR intensity method is described. It is assumed that the ratio of the integral absorption coefficients of the two reference bands at 1351 cm^?1 (gauche) and 1291 cm^?1 (trans), which both belong to the same type of vibration, is temperature independent. The two values ΔH = ?160 ± 40 cal Mol^?1 and ΔS = ?0.4 ± 0.5 cal (Mol · Grad)^?1 respectively. ΔS_U = ?1.8 ± 0.5 cal (Mol · Grad)^?1 thus determined agree well with the corresponding results obtained from NMR and electron diffraction measurements. However, from the pair of reference bands at 695 cm^?1 (gauche) and 1291 cm^?1 (trans), which do not belong to the same type of vibration, strongly differing values for ΔH and ΔSresult under the same assumption as above, which apparently is not applicable in this case.It is shown through these data that the “Fateley-Test” does not provide a suitable tool to decide whether the absorption coefficients of the reference bands are temperature independent or not. The reason for this insignificance is the relatively poor accuracy and reproducibility of measured IR band intensities obtainable up to now.The relative density of bicyclopropyl between ?60°C and + 50°C was determined.     

A thermodynamic and kinetic study on the stability of the conformational states of N-acetyl-proline-methylamide by IR. Spectroscopy and chemical relaxation

N-Acetyl-proline-methylamide (APMA) was synthesized by the mixed anhydride method and investigated by IR. spectroscopy and chemical relaxation measurements. The temperature-induced variation of the IR. absorption bands of the internally hydrogen bonded (b) and of the extended, unbonded (e) species at 3330 and 3450 cm^?1 respectively, were used to evaluate the molar absorptivities, a(b) = 280 and a(e) = 50 l/mol · cm, the equilibrium constant K = 0.70, and the molar enthalpy of reaction ΔH = ? 2280 ± 60 cal/mol. The entropy was estimated to be in the range ? 8 to ? 9 e.u. The reaction rates of this conformational transition were measured by the chemical dipole field effect. The relaxation time of the rate process is τ = 2.7 · 10^?9s, the rate constant for the formation of the hydrogen bond k(b) is 2.2 · 10⁸ s^?1, and that for the unfolding accompanied by the breakage of the amide hydrogen bond k(e) is 1.5 · 10⁸s^?1.     

On the polymerization mechanism of the Chromium(III) and Chromium(II)-B Silica Gel Catalysts

FTIR spectra of the chromium(III)/silica gel catalyst after short polymerization with ethylene show weak bands at 2 685 and 1 447 cm^?1 from the stretching and the deformation vibration of the methylene group, which binds the growing polymer to the active chromium(III) site. The band at 2 685 cm^?1 is reversibly removed by CO adsorption at low temperatures (?145°C). This adsorbed CO shows a broad band at 2 184 cm^?1. From the intensity of CO IR bands on unchanged chromium(III) before and after polymerization it was calculated that 12% of the chromium(III) is catalytically active, which is in good agreement with previous measurements by an entirely different determination method (11%). The chromium(II)-B catalyst showed also a weak band at 2 685 cm^?1 and it is therefore concluded that in this case the chromium(II) is oxidised by the ligating surface silanol group (in cooperation with an ethylene molecule). The band at 2 685 cm^?1 is discussed in relation to that from normal methylene groups at 2 925 and 2 855 cm^?1 and to that from the chromium(II)-A catalyst at 2 750 cm^?1. Evidence for the existence of a mononuclear chromium(II)-A species is found. This one is, in contrast to the dinuclear chromium(II)-A species, not polymerization active.     

Characterization of the Fe(III)‐binding Site in Sepia Eumelanin by Resonance Raman Confocal Microspectroscopy¶

The resonance Raman spectrum of Sepia eumelanin is discussed by analogy to model compounds containing catechol (CAT)‐like structural units. These data are then compared with the analogous data on Fe(III)‐enriched Sepia eumelanin. In contrast to the natural eumelanin, the Fe(III)‐enriched samples exhibit absorption features in the visible and near‐IR spectral regions, which are attributed to ligand‐to‐metal charge‐transfer (LMCT) bands. Resonance Raman spectra collected by exciting these LMCT bands reveal bands at 580 and 1470 cm^?1; the intensity of these features increases wioth increasing Fe(III) content. The 580 and 1470 cm^?1 bands are assigned to Fe‐OR stretching and ring deformation modes, respectively. These data further substantiate that the Fe(III)‐ melanin‐binding site in melanin is composed of CAT‐like structural units.     

Infrarot-Untersuchungen an substituierten Flavanonen und den isomeren 2′-Hydroxychalkonen

IR data of eight substituted flavanones and their isomeric hydroxychalkones have been recorded in order to assign the various absorption bands and to study the effect of substituents on C=C out-of-plane deformation (400–700 cm^?1), C?H out-of-plane deformation (700–1000 cm^?1), C?H in-plane deformation (1000–1300 cm^?1), C?O stretch (≈1200 cm^?1), OCH₃ (1200–1300 cm^?1), O?H deformation (1300–1400 cm^?1), CH₃ deformation (1300–1500 cm^?1), benzene ring vibration (1400–1600 cm^?1) and C=O stretch (≈1650 cm^?1). The δ_C?H (ring A) in 2′,4′-dihydroxy-3-nitrochalkone appears at 826 cm^?1 (s), while in the isomeric flavanone it shows up as three bands, viz., 807 (w), 833 (m) and 881 cm^?1 (w). This difference principally arises due to the presence of the electron withdrawing nitro substituent. The C=O stretching vibration in flavanones appears at a higher frequency than in the corresponding hydroxychalkones. This is perhaps due to the lack of conjugation in the former class of compounds. Chloro substituents (ring B) in different positions exert differing effects on ν_C?O. These differences can be rationalized in terms of a field-effect exerted by the chlorine atom.     

The effect of additives of strong inorganic acids on IR-spectroscopic determination of water in organic solutions

The possibility of the quantitative determination of water in organic solvents containing strong acids by IR spectrophotometry at 3500–3700 cm^?1 was studied. The molar absorption coefficients at the maximum of the most intense absorption bands of water in acetonitrile, chloroform, and 1,2-dichloroethane were 115, 43, and 88 M^?1 cm^?1, respectively. The study of the effect of acid additions to acetonitrile showed that hydrochloric and nitric acids had little on the shape and intensity of the IR spectra of water. The presence of perchloric acid reduces the intensity (for 0.027 M HClO₄, by 40% at 3618 cm^?1), which was due to the state of acids in the solvents. Conductometric measurements showed that, under these conditions, HCl and HNO₃ were unionized, while HClO₄ dissociated almost completely.     

Raman spectral changes during the solid-state polymerization of diacetylenes

Raman spectral changes resulting from the solid-state 1,4-addition polymerization of conjugated diacetylenes are reported. The monomers show an intense C?C stretching frequency near 2260 cm^?1, where as the polymers showed two strong bands, a C?C vibration near 2100 cm^?1 and a C?C vibration near 1500 cm^?1. The presence of both double and triple bonds in the polymers suggests the backbone structure (?C? C?C? C?)_n. The alternate mesomeric structure (? C?C?C?C? )_n can be eliminated as a possibility by the presence of the strong C?C vibration in the polymer. Sequential Raman spectra obtained during radiation-induced polymerization revealed intermediate spectral states between the initial monomer and final polymer. Intermediate-state vibrations first increase and then decrease in intensity as polymerization proceeds. However, the observed vibtrational frequencies of intermediate states were not dependent upon the extent of polymerization. Whether polymerization occurred thermally or as a result of radiation did not appear to influence the spectrum of the final polymer, but the observed number of intermediate states differed. Polymerization mechanisms, required molecular motions, and resulting structural changes are discussed.     

Metal-catalyzed oxidation of poly(α-methylstyrene) during surface-enhanced Raman scattering

Surface-enhanced Raman scattering (SERS) was used to characterize thin films of poly(α-methylstyrene) (PMS) spin-coated onto silver island films supported by glass substrates. At laser powers of a few tens of milliwatts, SERS spectra of thin films of PMS (about 100 Å) were weak, and only the bands near 1010 and 1040 cm^?1 were observed. At laser powers of about 100 mW, additional bands characteristic of PMS were observed near 720 and 1610 cm^?1. However, oxidative degradation of the PMS films to form graphite-like substances was also observed at the higher laser powers. When the thickness of the PMS films was increased to several hundred angstroms, degradation of the films was inhibited, but the intensity of the Raman scattering remained constant, indicating that the observed SERS was an interfacial rather than bulk effect. Degradation during SERS experiments was also inhibited by overcoating PMS films with much thicker films of poly(4-styrene sulfonate) (PSS). Scattering from the PSS overlayers was not observed as long as the thickness of the PMS films was greater than several tens of angstroms, again showing that the SERS was an interfacial effect. Oxidative degradation of the PMS films was also inhibited by adding a few percent of the antioxidant 2,6-di-tert-butyl-4-methylphenol to the polymer. Bands related to sulfite contaminants adsorbed onto the silver island films were observed near 640 and 940 cm^?1. These bands disappeared when PSS, but not PMS, was spin-coated onto the SERS substrates, indicating a strong interaction between PSS and silver.     

Near infrared spectroscopy of stearic acid adsorbed on montmorillonite

The adsorption of stearic acid on both sodium montmorillonites and calcium montmorillonites has been studied by near infrared spectroscopy complimented with infrared spectroscopy. Upon adsorption of stearic acid on Ca–Mt additional near infrared bands are observed at 8236 cm^?1 and is assigned to an interaction of stearic acid with the water of hydration. Upon adsorption of the stearic acid on Na–Mt, the NIR bands are now observed at 5671, 5778, 5848 and 5912 cm^?1 and are assigned to the overtone and combination bands of the CH fundamentals. Additional bands at 4177, 4250, 4324, 4337, 4689 and 4809 cm^?1 are attributed to CH combination bands resulting from the adsorption of the stearic acid. Stearic acid is used as a model molecule for adsorption studies. The application of near infrared spectroscopy to the study of this adsorption proved most useful.     

IR spectra of long-chain α,ω-alkanediols: 1,22-docosanediol and 1,44-tetratetracontanediol

The IR absorption spectra of α,ω-alkanediols with different chain lengths, HO(CH₂)₂₂OH and HO(CH₂)₄₄OH, in the spectral range of 400–5000 cm^?1 are analyzed. The assignment of numerous absorption bands to vibration modes in short methylene sequences and terminal hydroxyl groups is suggested. The splitting of IR absorption bands into doublets at 720–730 cm^?1 (rocking vibrations of CH₂ groups) and 1463–1473 cm^?1 (bending vibrations of CH₂ groups) testifies that the crystal unit subcells in the lamellae of alkanediols are orthorhombic with parameters typical of normal hydrocarbons. The specific features of absorption bands due to O-H stretching and C-O-H bending vibrations have been analyzed. These bands appear during formation of lengthy associates from hydrogen bonds formed by hydroxyl groups on the surface of elementary lamellae. A sharp increase in the intensity of the absorption bands in progression of C-C stretching and CH₂ wagging vibrations due to the anharmonic Fermi resonance with the stretching vibrations of C-O groups in the terminal hydroxyl groups has been detected.     

Structure analysis of a soluble polysiloxane-block-polyimide and kinetic analysis of the solution imidization of the relevant polyamic acid

A series of polysiloxane-block-polyimides were synthesized by solution imidization of the polyamic acids derived from the combination of 3,3′,4,4′-diphenylsulfonetetracarboxylic dianhydride (DSDA), 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), and diamino(polysiloxane) (PSX (M_w = 750)) in N-methyl-2-pyrrolidone (NMP). Their structures were analyzed by ¹H-, ¹³C-, and ²⁹Si-NMR spectra as well as by IR spectroscopy. The solid-state NMR spectrum was also measured to determine the spin–lattice relaxation time of the copolyimides. The observed relaxation times of both aromatic and polysiloxane segments were similar in the copolyimides having 10–30 wt % of PSX, while those in the copolyimide with 50 wt % of PSX was significantly different. This may be attributed to the morphology change due to the increase in PSX composition in the polymer backbone. The reduced viscosity of the copolyimides could be controlled by changing the monomer ratio in the feed or by adding an end-capping reagent such as phthalic anhydride into the polymerization system. The kinetic study of the solution imidization revealed that the imidization reaction obeyed second-order kinetics. The activation energy calculated for this imidization was 99.2 kJ/mol, being similar to that for the imidization of the DSDA-based aromatic polyimides. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2237–2245, 1998     

Study of the binding sites in the biomass of <Emphasis Type="Italic">Aspergillus niger</Emphasis> wild-type strains by FTIR spectroscopy

Fourier transform infrared (FTIR) spectroscopy studies were performed to confirm and to provide information on the identity and binding characteristics of the chemical groups responsible for the binding of elements using Aspergillus niger (A. niger) wild-type strains. Two absorption bands in the 3690–3615 and 2970–2895 cm^?1 regions can characterize stretching vibrations OH and CH groups in fatty acids, respectively, and intensive bands around of 1600 cm^?1 and by 1048 cm^?1 correspond to stretching vibrations of C=O groups of amides (amide I) or stretching vibrations ν(C–N). The FTIR results confirmed that no extra differences between IR spectra of A. niger in raw biomass and in solid rest after extraction with chloroform were observed. The small differences were observed in IR spectra of A. niger in chloroform after extraction.     

Theoretical study of electronic structure of rhodium mononitride and interpretation of experimental spectra

Potential energy curves of 22 electronic states of RhN have been calculated by the complete active space second‐order perturbation theory method. The X¹Σ₀⁺ is assigned as the ground state, and the first excited state a³Π₀+ is 978 cm^?1 higher. The ¹Δ(I) and B¹Σ⁺ states are located at 9521 and 13,046 cm^?1 above the ground state, respectively. The B¹Σ⁺ state should be the excited state located 12,300 cm^?1 above the ground state in the experimental study. Moreover, two excited states, C¹Π and b³Σ⁺, are found 14,963 and 15,082 cm^?1 above the X¹Σ⁺ state, respectively. The transition C¹Π₁–X¹Σ₀⁺ may contribute to the experimentally observed bands headed at 15,071 cm^?1. There are two excited states, D¹Δ and E¹Σ⁺, situate at 20,715 and 23,145 cm^?1 above the X¹Σ⁺ state. The visible bands near 20,000 cm^?1 could be generated by the electronic transitions D¹Δ₂–a³Π₁ and E¹Σ⁺₀–X¹Σ⁺₀ because of the spin–orbit coupling effect. © 2013 Wiley Periodicals, Inc.     

The IR spectrum of Pu(IV) polymer

The IR spectrum of Pu(IV) polymer has been measured from 200–4000 cm⁻¹. Major bands which could be associated directly with the oxygen-bridged polymer occured at 360 and 3400 cm⁻¹. These were assigned, respectively, to a PuO vibration similar to the lattice vibration of high-fired PuO₂ and to an OH stretching vibration of a water group which is either hydrated or occluded in the polymer structure. In addition, weaker bands were observed in the 1000 cm⁻¹ region which were correlated with the age of the polymer. The dried polymer precipitate was found to have a very great affinity for CO₂, absorbing it to form CO₃²⁻ groups which gave characteristic bands at 890 cm⁻¹ (v₂) and 1359, 1500 cm⁻¹ (split v₃). From chemical analyses, the carbon content of the polymer was found to be as high as 1.5 wt% when equilibrated in the room air.     

Structure and molecular conformation of tussah silk fibroin films: Effect of methanol

Structural changes of tussah (Antheraea pernyi) silk fibroin films treated with different water-methanol solutions at 20°C were studied as a function of methanol concentration and immersion time. X-ray diffraction measurements showed that the α-helix structure, typical of untreated tussah films, did not change for short immersion times (2 min), regardless of methanol concentration. However, crystallization to β-sheet structure was observed following immersion of tussah films for 30 min in methanol solutions ranging from 20 to 60% (v/v). IR spectra of tussah films untreated and methanol treated for 2 min exhibited strong absorption bands at 1265, 892, and 622 cm^?1, typical of the α-helix conformation. The intensity of the bands assigned to the β-sheet conformation (1245, 965, and 698 cm^?1) increased for the sample treated with 40% methanol for 30 min. Raman spectra of tussah films with α-helix molecular conformation exhibited strong bands at 1657 (amide I), 1263 (amide III), 1106, 908, 530, and 376 cm^?1. Following α → β conformational transition, amide I and III bands shifted to 1668, and to 1241, 1230 cm^?1, respectively. The band at 1106 cm^?1 disappeared and new bands appeared at 1095 and 1073 cm^?1, whereas the intensity of the bands at 530 and 376 cm^?1 decreased significantly. ©1995 John Wiley & Sons, Inc.