Metal—nitrogen stretching assignments in some metallophthalocyanines and μ-oxo-(Fephthalocyanine)2

Metal-isotope substitution has been employed to establish the absorptions in the i.r. spectra of some metallophthalocyanines that contain MN stretching motion. The primary MN stretching bands appear at 240.7 cm⁻¹ in ⁶⁴Znpc; 284.0 cm⁻¹ in ⁶³Cupc; 376.0 cm⁻¹ and 317.8 cm⁻¹ in ⁵⁸Nipc; and 308.4 cm⁻¹ in ⁵⁴Fepc. Assignment of the far-i.r. spectrum of u-oxo-(Fepc)₂ places the FeN stretching band at 280.2 cm⁻¹ and suggests a linear arrangement of the FeOFe with Fe atoms in the plane of the phthalocyanine ring.     

Vibrational spectrum,force Field calculations,thermodynamic functions and barrier to internal rotation for benzoyl fluoride

The i.r. and Raman spectra of benzoyl fluoride have been studied in solid, liquid and vapour phases. All of the 36 normal modes of vibration have been assigned in the light of normal coordinate analysis. The carbonyl group stretching mode exhibits a broad band group at ∼ 1800 cm⁻¹, with three bands of comparable intensities. The appearance of the triplet is explained by the existence of strong Fermi resonance. The CO stretch, CF stretch and CFO wag modes have been confidently assigned at 1810, 1014 and 682 cm⁻¹ (in solid/liquid state spectra), respectively. The former two of these show an upward shift and the latter one shows a downward shift in going from solid phase to vapour phase. These results evidence the presence of strong intermolecular interactions in solid and liquid phases. Thermodynamic functions and barrier to internal rotation of the CFO group have also been computed using the fundamental frequencies. The barrier height is found to be ∼4.91 kCal/mole.     

Infrared matrix isolation studies of the trimethylamine oxide—hydrogen chloride complex

The reaction products of the codeposition of trimethylamine oxide and a HCl/Ar mixture are characterized by diffuse absorption in the region from 1850 to ca 3200 cm⁻¹ and by a strong band at 1700 cm⁻¹. These absorptions are assigned respectively to the OH⁺...Cl⁻ antisymmetric stretching and in-plane bending modes, which indicates that proton transfer to basic oxygen occurs.     

Frequences infrarouges et Raman caracteristiques de cyclopropyl- et (cyclopropylmethyl)trimethylsilanes: Comparaison avec les vinyl- et allyltrimethylsilanes—III

The i.r. and Raman spectra of 20 compounds with a trimethylsilyl group linked to either a cyclopropane ring or a vinyl or allyl radical have been recorded between 400 and 4000 cm⁻¹. The experimental results and the vibration frequency assignments, especially the symmetrical SiC_n stretching, show that there are two classes of derivatives characterized by analogous SiC spectra: (1) the vinyl- and cyclopropyltrimethylsilanes and (2) the allyl- and (cyclopropylmethyl)trimethylsilanes. The spectroscopic behavior of each class is consistent with its observed chemical reactivity. A distinction can also be made between some structural isomers on the basis of the SiC stretching or other frequencies.     

Raman spectroscopic study of (CH3NH3)2HgCl4 in the high-temperature range

A Raman spectroscopic study of (CH₃NH₃)₂HgCl₄ is reported in the temperature range 299–373 K. Discontinuities in the HgCl symmetric stretching mode and in the frequency shift of the CN stretching mode indicate a new phase above 330 K. A non-linear increment of the widths of these bands confirms the transition. Arrhenius behaviour of the CN stretching mode indicates a barrier of 1234 cm⁻¹.     

Integrated absorption intensities of haloethanes and halopropanes

The infrared absorption intensities of the chlorofluorocarbons C₂Cl_xF_y, (x + y = 6); the hydrofluorocarbons C₂H_xF_yH (x + y = 6); and a number of hydrochlorofluorocarbons, including some members of the propane series, have been measured. Absorption intensities have been obtained by integration over specified ranges of frequencies. The ranges used include the atmospheric window (1250t-833 cm⁻¹), 3500-450 cm⁻¹, 1300-700 cm⁻¹, and those for selected individual absorption bands. Comparisons of the results have been made with published work where available, and attention is drawn to possible sources of error in the measurement of band areas. The spectra of the halopropanes have been included for the range 3500-150 cm⁻¹. A preliminary study has been made of the relation between the number of fluorine atoms in the molecule and the intensity of absorption of the CF stretching vibrations.     

Surface-enhanced Raman spectroscopic study of the metal—sulfur bonding: Adsorption of N,N-dimethyl-thioformamide on copper and silver electrodes

Surface-enhanced Raman spectroscopy has been used to study the adsorption of N,N-dimethyl-thioformamide (DMTF) on Cu and Ag electrodes. Similar to the cases of thiourea and thioacetamide, the predominantly CS stretching band at 975 cm⁻¹ of DMTF is shifted to lower frequencies by about 30–40 cm⁻¹ upon adsorption on Cu and Ag surfaces. We conclude that DMTF is S-bonded to the metal surfaces. The frequency shifts of the CS stretch resemble those observed for the organometallic complexes of DMTF.     

Infrared emission spectrum of HNO: The ν1 band

HNO has been observed in emission from a radiofrequency discharge through a mixture of ammonia and oxygen. The ν₁ (NH stretching) band in the region 2400–3200 cm⁻¹ has been recorded with a Fourier transform spectrometer using an apodized resolution of 0.04 cm⁻¹. The analysis of the band has been extended to higher K values than in earlier work.     

Vibrational spectra of tetramethyleyclobutane-1-one-3-thione and the fully deuterated derivative

Raman and i.r. spectra of tetramethylcyclobutane-1-one-3-thione (TMCBOT) and the fully deuterated derivative TMCBOT-_d¹² have been recorded. A fairly complete set of vibrational frequencies and assignments are given for the two molecules. The CO stretching mode was observed as a very strong Fermi doublet in the infrared spectrum of TMCBOT at 1811/1782 cm⁻¹. For TMCBOT-d₁₂ a similar doublet was observed at 1808/1775 cm⁻¹. The CS stretching mode was assigned to bands at 1303 cm⁻¹ for TMCBOT and 1307 cm⁻¹ for the deuterated molecule.     

CH local modes in cyclobutene—I. FTIR studies 700–9000 cm−1

The vibrational structure of CH stretching states in gas-phase cyclobutene was studied using FTIR spectroscopy in the range 700–9000 cm⁻¹. The structure was modelled using two effective vibrational Hamiltonians, one for each type of CH bond present, consisting of local mode basis functions subject to coupling with symmetrically equivalent bonds and to Fermi resonances with suitable low frequency vibrations. Best-fit model parameters were determined using least-squares routines and the model predictions are compared to the observed band positions and intensities. Some discussion is given of the relevance of the observed couplings to intramolecular vibrational redistribution (IVR) which results in the observation of statistical behaviour in cyclobutene isomerization induced by excitation of CH stretching overtones in the visible region.     

Vibrational circular dichroism studies of molecular conformation and association of dipeptides

Vibrational circular dichroism (VCD) and infrared (IR) absorption spectra in the NH stretching region have been measured for the dipeptides, R′COAANHR′'(R′ = Me and tertBu; AA = Ala, Leu, Val and Phe; R′' = Me, isoBu and neoPe). Analyses of the VCD and absorption spectra indicated that the VCD bands for the NH stretching are quite sensitive to the state of hydrogen bonding as well as the local conformation of oligopeptides. VCD spectra exhibit a negative VCD band at 3420-3405 cm⁻¹ due to the C₅ conformer with an intramolecularly hydrogen-bonded five-membered ring. The intermolecularly hydrogen-bonded NH stretching vibration exhibits a characteristic negative—positive couplet from the high wavenumber side due to the antiparallel C₅C₅ dimer formation. Hydrogen-bonded oligomers beyond the dimer formed in highly concentrated solutions give rise to an additional negative VCD band on the lower wavenumber side of the hydrogen-bonded absorption band.     

Theoretical prediction of vibrational spectra. Scaled quantum mechanical (SQM) force field for fluorobenzene

The complete harmonic force field of fluorobenzene has been determined from ab initio Hartree-Fock calculations using the 4–21 Gaussian basis set. As force constants are systematically overestimated at this level of theory, the directly calculated force field was scaled by empirical factors taken over from benzene and methylfluoride. Except for a slight overestimation of the CF stretching frequency, the scaled quantum mechanical (SQM) force field obtained in this way reproduces the experimental fundamental frequencies of the parent molecule and two deuterated isotopomers within 20 cm⁻¹ (with mean deviations below 12 cm⁻¹), and experimental assignments are analyzed on this basis. Theoretical i.r. intensities reproduce the main features of the spectra fairly well.     

An in-plane force field for some benzene derivatives having unsaturated substituents

A simplified in-plane overlay valence force field has been developed for some benzene derivatives that have unsaturated substituents. The molecules used in the optimization of the force constants are benzene, styrene, benzaldehyde, ethynylbenzene and m- and p-diethynylbenzene. The force field comprises 57 force constants, out of which 33 have been transferred from our other overlay calculations and 24 are optimized on about 600 experimental frequencies, giving an rms frequency deviation of 10.5 cm⁻¹ which includes the CH stretching vibrations. Some revisions in the assignments have been made. For comparison a fully independent overlay force field has been optimized for some methyl substituted benzenes using the same approximations in the force field. The transferability of force constants and limitations of the transferability are discussed.     

Structural evolution of poly(lactic acid) upon uniaxial stretching investigated by in situ infrared spectroscopy

Structural evolution of poly(lactic acid) (PLA) upon uniaxial stretching was studied with in-situ polarized infrared spectroscopy measurements, and its structural change affected by annealing was also investigated. Band shifting was used to reflect the structural ordering process. It was found that the band at 1302 cm⁻¹ always moves to low wavenumbers before crystallization, indicating the occurrence of intermolecular packing ordering. However, the band at 869 cm⁻¹ shifts to high wavenumbers, which is related to the transition from the amorphous phase to the ordered phase. Interestingly, during stretching, the shifting for the band at 1302 cm⁻¹ always occurs before that for the lower wavenumber band, whereas these two band shifts take place simultaneously under annealing. Based on the different characteristics of the structural evolution under stretching and annealing processes, a critical temperature was found at around 63 °C, which influences the effect weight of kinetic and thermodynamic factors to the crystallization behavior. The effect of the drawing temperature on crystallization and mechanical property of PLA films was also analyzed.     

Scaled quantum mechanical (SQM) force field and theoretical vibrational spectrum for benzonitrile

The complete harmonic force field of benzonitrile has been determined by ab initio Hartree—Fock calculations using a 4–21 Gaussian basis set. As force constants are systematically over-estimated at this level, the directly calculated force field was scaled by empirical factors previously optimized for benzene and HCN. Frequencies calculated from this scaled quantum mechanical (SQM) force field confirm the published experimental assignments for benzonitrile, benzonitrile-p-d and benzonitrile-d₅. Aside from the CH (and CD) stretching frequencies, which are strongly affected by anharmonicity, the mean deviation between the observed and calculated frequencies is below 9 cm⁻¹ for each isotopomer. Theoretical i.r. intensities reproduce the main features of the spectra semiquantitatively.     

Far infrared spectra of zeovaent platinum—acetylene complexes

The low frequency IR spectra of a series of (Ph₃P)₂Pt(HC7z.tbnd;CR) complexes have been measured in the range 600–300 cm^?1. PtP and PtC stretching frequencies have been assigned by comparison with spectra of similar platinum complexes.     

Distinguishing and identifying hydrogens in an NH3 group by I.R. spectroscopy

Combined low temperature isotopic dilution and polarized i.r. measurements have been performed on single crystal specimens of sulfamic acid, ⁺H₃NSO₃⁻, containing 5% D with respect to H. The three isotropically isolated νND bands observed in these spectra at 2302.5, 2313 and 2324 cm⁻¹ were polarized along different crystallograpkic axes, which allowed to assign them to specific hydrogen positions in the crystal and in the NH₃ groups. Comparison of neutron diffraction and vibrational frequency data shows that, despite the differences in NHO hydrogen angles, of all the geometric parameters the N⋯O distance only seems to correlate with the isolated N-D stretching frequencies.     

Vibrational study of strong CH · middot; X hydrogen bonds in solid complexes of boron decachlorocarboranes

Solid complexes of boron decachloro-o-carborane and boron decachloro-m-carborane (B₁₀Cl₁₀C₂H₂) with some oxygen and nitrogen bases have been investigated by infrared and Raman spectroscopy. Complexes containing CH · · O hydrogen bonds are characterized by a relative CH stretching frequency shift up to 12% and a halfwidth of the νCH band up to 220 cm^?1. CH · · N hydrogen bonds, with trimethylamine for example, are stronger with a relative shift of about 18% and $\text{ν}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ of about 500 cm^?1. Triethylamine complexes, however, form a NH⁺ · · C^? proton transfer hydrogen bond while pyridine can give either CH · · N or C^? · · ⁺HN hydrogen-bonded adducts depending on the solvent and temperature. The CH · · N?c^? · · ⁺HN equilibrium appears to be shifted towards ion-pair formation at considerably smaller enthalpy values compared to the OH · · N?O^? · · ⁺HN system. CH and NH stretching frequencies are correlated with the acidity of the donor and the basicity of acceptor molecules.     

Mise en evidence des vibrations de la liaison CH dans des motifs structuraux de type alkylidène cyclopropane

The CH bond vibrations in alkylidene cyclopropanic compounds

have been assigned according to experimental results based on vibration—rotation structures, Raman depolarisation ratios, isotopic substitution and solvent effects. They are found at: 3072-3050cm⁻¹ (vCH), 1100-1050 cm⁻¹ (δCH) and 736-700 cm⁻¹ (γCH).