Group Frequency Correlations Research Articles

The vibrational spectra of norbornene and nadic anhydride

The vibrational spectra of norbornene (bicyclo[2,2,1]hept-2-ene) and nadic anhydride (cis-endo-5-norbornene-2,3-dicarboxylic anhydride) have been investigated by infrared, Raman and inelastic neutron scattering spectroscopies and density functional theory (DFT). For norbornene, the five missing fundamentals have been located. In the C–H stretch region, the infrared and Raman spectra synthesised from the DFT calculations are shown to be in poor agreement with the experimental spectra. Visualisation of the C–H stretch modes shows that assignments made on the basis of group frequency correlations are incorrect. Nadic anhydride has not been previously investigated by vibrational spectroscopy. This paper demonstrates that with state-of-the-art inelastic neutron scattering spectra it is possible to successfully analyse complex systems that have not been studied before.

Vibrational Spectra and Assignments for 3,4-Dibromothiophene

Abstract The infrared spectrum of 3,4-dibromothiophene has been studied from 4000 to 200 cm−1. The Laser Raman spectrum has also been recorded and depolarization values have been measured. An assignment of the 21 fundamental vibrations is proposed based on group frequency correlations, Raman polarization data and comparison with the spectra of parent and some halogeno-substituted molecules.

Internal modes by Raman and infrared spectroscopy of benzylidenemalononitrile

The polarized Raman spectra of a single crystal of benzylidenemalononitrile (BMN), as well as the infrared spectrum of a powder sample, have been measured. An assignment of the 48 fundamental vibrations is proposed, based on group frequency correlations, Raman and i.r. intensities and comparison with the spectra of parent molecules.

Vibrational spectra and structure of halogen‐substituted cyclopropanes. III—cis‐ and trans‐1, 2‐diiodocyclopropane

AbstractThe infrared spectra of liquid cis‐ and trans‐1, 2‐diiodocyclopropane were measured from 4000 to 200 cm−1. Raman spectra between 4000 and 50 cm−1 of the two compounds as liquids and of the solid cis isomer were also obtained. All of the 21 normal vibrations of the two molecules were convincingly assigned on the basis of Raman depolarization ratios and group frequency correlations. Comparisons are made with the normal modes of related compounds. There is excellent agreement with those assignments previously proposed for the two isomers of 1, 2‐dibromocyclopropane, cis‐1, 2‐dichlorocyclopropane and related modes of iodocyclopropane.

Infrared Group Frequency Correlations for Styrenes, α-Methylstyrenes, and Related Compounds

Infrared group frequency correlations are presented which aid in spectra-structure identification of styrenes, α-methylstyrenes, and related compounds. The vinyl and phenyl groups in styrene are coplanar in only those cases where atoms or groups such as Cl and CH3 are not substituted in the 2,6-positions, and the isopropenyl and phenyl groups in α-methylstyrenes are coplanar in only those cases where atoms or groups such as Cl and CH3 are not substituted in one ortho-position. Steric factors prevent the vinyl and phenyl groups from being coplanar in styrene substituted with atoms or groups in at least the 2,6-positions, and steric factors also prevent the isopropenyl and phenyl groups from being coplanar in 2-substituted α-methylstyrenes.

Vibrational Spectra of Pentachlorocyclopropane

AbstractInfrared spectra (4000–400 cm−1) of pentachlorocyclopropane have been recorded for all three of its physical states. A liquid‐phase Raman spectrum of this molecule has also been observed. Based on the Raman depolarization data, gas‐phase infrared band contours and expected group frequency correlations, it has been possible to propose an assignment for 20 of the 21 normal vibrations of pentachlorocyclopropane. This assignment agrees well with those proposed for hexachlorocyclopropane, the three isomeric tetrachlorocyclopropanes, 1,1‐dichlorocyclopropane and chlorocyclopropane. Further, the vibrational assignment for pentachlorocyclopropane has identified characteristic vibrational frequencies for the three CH(X) modes: CH stretch, 3040 cm−1; in‐plane CH bend, 1296 cm−1; and out‐of‐plane CH bend, 1088 cm−1.

Vibrational spectra and assignments for 2,3-dibromothiophene and 2,3,5-tribromothiophene

The infrared spectra of 2,3-dibromo- and 2,3,5-tribromothiophene have been studied from 4000 to 200 cm −1. The Laser Raman spectra have also been recorded and depolarization values have been measured. An assignment of the 21 fundamental vibrations is proposed based on group frequency correlations, Raman polarization data and comparison with the spectra of parent and some halogeno-substituted molecules.

Vibrational spectra and assignments for 3-halogeno-derivatives of thiophene

The i.r. spectra of 3-chloro-, 3-bromo- and 3-iodothiophene as liquids and solids at 100 K have been studied from 4000 to 250 cm −1. The laser Raman spectra of liquids have also been recorded and depolarization values have been measured. An assignment of the 21 fundamental vibrations is proposed based on group frequency correlations, Raman polarization data and comparison with the spectra of parent molecule.

Vibrational spectra and assignments for 2-chloro and 2-bromo derivatives of thiophene, selenophene and tellurophene

The infrared spectra of 2-chloro-, 2-bromo-thiophene, -selenophene and -tellurophene as liquids have been investigated from 4000 to 300 cm −1. The laser Raman spectra of these liquids have also been recorded and depolarization values have been measured. An assignment of the 21 fundamental vibrations is proposed, based on group frequency correlations, Raman polarization data and comparison with the spectra of parent molecules.

Infrared and Raman group frequency correlations: Substituted oxamides

Infrared and Raman spectra of N,N′-dialkyl oxamides and N,N′-diaryl oxamides or ( N,N′-oxanilides) were recorded, and characteristic group frequencies useful in spectra-structure identification are presented. The i.r. and Raman data recorded for N,N′-dialkyl or N,N′-diaryl oxamides in the solid phase can be explained on the basis that they exist in an intermolecularly hydrogen bonded trans configuration where each oxamide group can be viewed as having C 2 h symmetry. In the vapor phase, N,N′-dimethyloxamide also exists in the trans configuration. Evidence is presented that suggest N,N,N′,N′-tetraethyloxamide exists as rotational isomers in solution, and that these are the trans and gauche structures.

Spectra and structure of small ring compounds. XXXVI. 1-methylcyclopentene and 1,2-dimethylcyclopentene

The i.r. spectra of solid and gaseous 1-methylcyclopentene and 1,2-dimethylcyclopentene were recorded from 4000 to 33 cm −1. The corresponding Raman spectra of the gases and liquids were measured. The fundamental vibrations of each compound have been assigned on the basis of group frequency correlations, band intensities, band contours and Raman depolarization values. The barrier hindering internal rotation of the methyl group has been calculated to be 1.93 kcal/mol for 1-methylcyclopentene. In 1,2-dimethylcyclopentene the methyl barrier is 1.77 kcal/mol for the B 2 vibrational mode.

Raman spectra and vibrational assignments for deuterated membrane lipids: 1,2-Dipalmitoyl phosphatidylcholine-d 9 and -d 62

Vibrational Raman spectra of polycrystalline 1,2-dipalmitoyl phosphatidylcholine-d 9 (fully deuterated choline methyl groups) and 1,2-dipalmitoyl phosphatidylcholine-d 62 (fully deuterated acyl chains) were recorded in the 2800–3050, 2050–2250 and 700–1800 cm −1 regions. The fundamental vibrational modes were assigned primarily on the basis of isotopic frequency shift ratios, group frequency correlations and comparisons with specific model compounds. Since deuterium-substituted lipids provide well-isolated spectral probes, particularly in the carbon-deuterium stretching region, the dependence of the 2050–2250 cm −1 region on lipid phase was examined for the dipalmitoyl phosphatidylcholine-d 62 species. The methylene CD 2 deformation and twisting modes at 984 and 919 cm −1, respectively, also exhibit intense, isolated vibrational transitions which should prove useful for monitoring molecular order in mixed deuterated and undeuterated lipid systems. Except for the relatively weak choline methyl C-D and C-H stretching modes, the spectrum of 1,2-dipalmitoyl phosphatidylcholine-d 9 is not distinguishable from that of the undeuterated system. For both the d 9 and undeuterated species, the vibrational modes associated with the lipid head group region are sensitive to slight hydration.

Vibrational spectra of several fluorine-substituted allene molecules

The i.r. spectra (200–4000 cm −1) of gaseous and the Raman spectra (0–4000 cm −1) of both gaseous and liquid H 2CCCF 2, HDCCCCF 2, D 2CCCF 2, F 2CCCF 2, H 2CCCHF, FHCCCHF and F 2CCCHF have been recorded and the data interpreted in detail. The normal modes for these molecules have been assigned on the basis of the i.r. band contours, the depolarization ratios, the observed isotopic shifts, and group frequency correlations. Normal coordinate calculations have been carried out for the 1,1-difluoroallene and tetrafluoroallene molecules. For the 1,1-difluoroallene molecule, extensive mixing was found between the symmetric CCC stretch and the symmetric CF 2 stretch whereas less extensive mixing was found for the CF 2 wag with the CCC out-of-plane bend, the CF 2 scissors with the CCC symmetric stretch, and the CCC in-plane bend with the CF 2 rock. For the tetrafluoroallene molecule, extensive mixing was found for the antisymmetric CCC stretch and the out-of-phase symmetric CF 2 stretch.

Vibrational spectra and assignments for tetrahydrothiophene, tetrahydroselenophene and tetrahydrotellurophene

The i.r. spectra of tetrahydrothiophene, -selenophene and -tellurophene as liquids and solids at 100K have been studied from 4000- to 250 cm −1. The Raman spectra of liquids have also been recorded and depolarization values have been measured. An assignment of the 33 fundamental vibrations for the 3 molecules is proposed based on depolarization values, dichroic behaviour and group-frequency correlations.

Vibrational spectra of ethyl iodedes

The infrared spectra of CH 3CH 2I, CD 3CH 2I, and CH 3CD 2I of the vapors and the solids at 170°C have been recorded from 4000-200 cm −1. The Raman spectra of the liquids and vapors have also been recorded and depolarization values have been measured. Assignment of the eighteen fundamental vibrations has been based on depolarization values, band contours, group-frequency correlations, and normal coordinate calculations. A critical discussion of the CH stretching assignments in CH 3CH 2X molecules is presented.

L'étude vibrationnelle du paraquat

AbstractRaman and IR spectra of solid powders and solutions of paraquat and derivatives are reported. The fundamental vibrations of each compound have been assigned on the basis of group frequency correlations, isotopic substitution (shifts) and band intensities, as well as depolarization values when applicable.

The vibrational spectra of 3,3‐difluoroxetane

AbstractRaman spectra of 3, 3‐difluoroxetane have been recorded from 50 to 3500 cm−1 in all three physical states. In addition, the infrared spectra of gaseous and solid 3,3‐difluoroxetane have been measured between 200 and 3500 cm−1. A vibrational assignment is presented in terms of the C2ν point group which is based upon the observed band contours, depolarization ratios, group frequency correlations and relative band intensities. Although transitions associated with the ring‐puckering mode of 3,3‐difluoroxetane were not directly observed, a weak absorption at 1228 cm−1 has been assigned to a combination band involving the out‐of‐plane skeletal bending and a CH2 wagging mode. With this assignment, the 1 ← 0 transition of ν24 is estimated to be centered near 69 cm−1. The data reported herein will be compared with other studies on similar ring systems.

Spectra and structure of small ring compounds. XXXI Microwave, Raman and infrared spectra, conformation, dipole moment, and quadrupole coupling constants of 2-oxazoline

The microwave spectrum of 2-oxazoline has been recorded from 12.4–40.0 GHz. Both Q-branch and R-branch assignments have been made for the ground and five vibrationally excited states of the ring puckering mode for both A - and B-type transitions. The components of the diple moment were determined by the Stark effect to be μa = 1.14±0.01, μb = 1.35±0.01, μc = 0.00±0.00, and μt = 1.77±0.01 D. The quadrupole coupling constants were found to have the following values: χa a = −3.54, χb b = 2.03, and χc c = 1.51 MHz. From the inertial defect Δc and the dipole moment, it is concluded that the heavy atom skeleton is planar. From the relative intensity measurements, the first excited state of the ring puckering vibration was found to have a frequency of 79±8 cm−1 and from a series of difference bands in the infrared spectrum, the ν = 0→1, 1→2, 2→3, 3→4, and 4→5 transitions were found to have the following frequencies: 74, 95, 103, 110, and 117 cm−1, respectively. The potential function governing the ring puckering motion was found to be of the form V = 22.2 (Z4+1.31Z2), where Z is the reduced ring puckering coordinate. The Raman spectra of gaseous, liquid, and solid 2-oxazoline was investigated from 0–3500 cm−1 and the infrared spectra of the gas and solid were recorded from 33–3500 cm−1. The vibrational assignment of the fundamentals is proposed which is consistent with the Cs conformation. The assignment is based on the gas-phase band contours, the depolarization values, and group frequency correlations. The number of lattice modes indicate that there are at least two molecules per primitive cell. The results are compared with those obtained for other similar five-membered rings.

Gas and matrix infrared spectra of n-methyl-ethylidenimine and valence force field

Infrared spectra of gaseous and matrix isolated trans-CH 3N:CHCH 3, CD 3N:CHCH 3 and CH N:CDCD 3 have been recorded from 4000 to 200 cm −1 under medium resolution. Nearly complete assignments have been established based upon rotational contours, isotope shifts and group frequency correlations. A number of Fermi resonances have been detected mainly related to CH(D) stretching fundamentals. ln particular, the light N-methyl group gives rise to a complicated Fermi multiplet in the CH-stretching region. An examination of Q sub-band structures resulted in the identification of a number of Coriolis resonances, which in most cases involve pairs of nearly coinciding ‘E-type“ methyl deformation fundamentals. The rotational fine structure of three bands has been analysed by means of combination differences providing estimates for effective rotational constants A( u)- 1 2 [ B( u)+ C( u)]. From a normal coordinate analy a 30 parameter valence force field has been obtained, which allows an approximation of 85 experimental frequencies with an RMS deviation of 7.4 cm −1.

Vibrational spectra and structure of esters—I. Infrared and Raman spectra of CH 3COOCH 3, CH 3COOCD 3, CD 3COOCH 3 and CD 3COOCD 3

The infrared spectra of gaseous, liquid and solid methyl acetate and its deuterium derivatives have been investigated from 4000 to 200 cm −1. The absorption spectrum of the crystalline state of each isotope has also been measured down to 33 cm −1, but the methyl torsional modes were not resolved. Raman spectra of the gaseous, liquid and solid states were obtained between 100 and 4000 cm −1. It is concluded that methyl acetate is present as a single molecular conformation in the temperature range studied since there is a one to one correspondence between the infrared and Raman transitions measured at ambient and liquid nitrogen temperatures. An assignment of the 27 normal modes, based upon relative band intensities, isotopic shift ratios and group frequency correlations is presented.