IR Band Intensities Research Articles

Measurement of the integral intensities of IR bands of crystalline substances in a polyethylene matrix

Measurement of the integral intensities of IR bands of crystalline substances in a polyethylene matrix

Study of the electron interactions of polysubstituted azoles by PMR and IR spectroscopy

The IR and PMR spectra of an extensive series of methyl derivatives of aromatic and heteroaromatic compounds were investigated. With a few exceptions, the experimental data on the chemical shifts of the protons \((\delta ^{{\text{CH}}_{\text{3}} } )\) and the intensity of the band of the symmetrical stretching vibration [(ACH)1/2] for five- and six-membered heterorings can be united in a single reaction series with polysubstituted toluenes within the framework of an additive scheme. The (ACH)1/2 values correlate satisfactorily with the calculated (by the CNDO/2 method) total charges on the carbon and hydrogen atoms of the methyl group. In contrast to the intensities of the IR bands, linear relationships between the chemical shifts and the charges on the hydrogen atoms are observed only within the limits of particular reaction series. The lack of a unified relationship was interpreted as being the result of the effect of the ring current, the contribution of which to the \((\delta ^{{\text{CH}}_{\text{3}} } )\) value depends on the nature of the heteroatom.

Vibrational frequencies, gauche dihedral angle and energy difference between rotational isomers of β-bromopropionitrile

Infrared absorption intensities of fundamental bands of β-bromopropionitrile CH 2BrCH 2CN were measured in the liquid state and the energy difference between the trans and gauche isomers was determined by applying the absolute intensity method. Normal frequencies and IR band intensities were computed for various dihedral angles for the gauche isomer to compare with observed values. As a result, the dihedral angle of the gauche isomer was determined as 105°. On the basis of computed frequencies and intensities and by referring to previous vibrational assignments, the fundamental frequencies of β-bromopropionitrile, especially for the trans isomer, were determined. From the converged value of the trans population ratio parameter the energy difference was determined as −0.57 ± 0.10 (kcal mol −1), which is in good agreement with previously obtained values. This fact confirms the validity of the absolute intensity method for obtaining an energy difference between rotational isomers.

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 Δ H and entropy Δ S 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 Δ H = −160 ± 40 cal Mol −1 and Δ S = −0.4 ± 0.5 cal (Mol · Grad) −1 respectively. Δ S 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 Δ H and Δ Sresult 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.

Über die bestimmung von isomerisierungsenthalpien und -entropien mit der IR-intensitätsmethode

Among the many sources of error which may affect the results for the enthalpy Δ H and entropy Δ S of isomerization determined by the IR-intensity method, the influence of the temperature dependence of the absorptivities of the reference bands, α g( T) and α t ( T), is studied theoretically. Based on the general case I, the following three special cases II–IV are examined, in which increasingly stronger constraints are imposed on the compound-specific functions α g ( T) and α T ( T): II. Constant ratio α g ( T)/α T ( T), III. α g ( T) and α T ( T) both temperature independent and different, IV. α g ( T) and α T ( T) both temperature independent and equal. For each case the formulae for the evaluation of Δ H and Δ S as well as the kind and the number of the quantities to be measured are given. Moreover, in the cases I and II new methods for the analysis of the measured data are suggested. In each case the plots of the normalized band intensities A g and A t and the temperature T versus each other in different two-dimensional diagrams have been examined to find out whether one of the simpler special cases is applicable for the respective pair of reference bands. It is shown that these plots are not a suitable tool because of the relatively poor accuracy and reproducibility of measured IR-band intensities obtainable up to now.

Infrared Spectra and Structure of Substituted Unsaturated Carbonyl Compounds. XIX. Four Component Conformational Equilibria in β-Ketoaldehyde Trans Enol Ethers

Abstract Acylic aliphatic trans β-alkoxy-α,β-unsaturated ketones, R1COCR2=CHOR3, have been shown to exhibit restricted rotation around both the Csp2–Csp2 and Csp2–O single bonds. The conformational equilibria between the EZZ, EEZ, EZE and EEE rotamers, estimated from comparison of the IR band intensities, are dependent on the steric requirements of the alkyl substituents. The sequence of the νC=O and νC=C vibrational frequences is νC=O(s-cis/O-s-trans)>νC=O(s-cis/O-s-cis)>νC=O(s-trans/O-s-trans)>νC=O(s-trans/O-s-cis)>νc=C(s-trans/O-s-trans)>νC=O(s-trans/O-s-cis)>νC=C(s-cis/O-s-trans)>νC=C(s-cis/O-s-cis). The wave number differences ΔνC=CC=O(s-cis/O-s-trans)=75–85 cm−1, ΔνC=CC=O(s-cis/O-s-cis)=80—100 cm−1, ΔνC=CC=O(s-trans/O-s-trans)=20—30 cm−1 and ΔνC=CC=O(s-trans/O-s-cis)=35–50 cm−1.

ChemInform Abstract: BAND INTENSITIES IN THE IR SPECTRA OF METAL CARBONYL COMPLEXES, NI AND CO TETRACARBONYLS

Abstract The IR band intensities of Ni and Co tetracarbonyls were measured and the dipole moment derivatives of the compounds were calculated. The effective charges on C and O atoms were estimated using the procedure suggested in a previous paper.

Band intensities in the IR spectra of metal carbonyl complexes, Ni and Co tetracarbonyls

The IR band intensities of Ni and Co tetracarbonyls were measured and the dipole moment derivatives of the compounds were calculated. The effective charges on C and O atoms were estimated using the procedure suggested in a previous paper.

Formation of carbonium ions on zeolite surfaces

The adsorption and thermal desorption of carbonium ions from surfaces of zeolites, Al 2O 3 and TiO 2 have been investigated spectroscopically. The formation of stable carbonium ions (Φ 3C +) of triphenylmethyl compounds (Φ 3CCl and Φ 3COH) occurred at relatively low temperatures, e.g. 100°C. No Φ 3C + ions could be detected after adsorption of triphenylmethane. These findings are in agreement with prior mass spectrometric results. Intensities of the respective IR bands indicate that the molecules (Φ 3CCl, Φ 3COH, Φ 3CH) penetrate into the interior of the zeolite grains, where they are adsorbed. The experiments show that acidic Lewis sites are responsible for the carbonium ion formation in the present system.

Near IR spectra of long chain vinyl derivatives

AbstractThe near IR spectra of a series of compounds derived from long chain fatty acids and containing the vinyl structure were examined. These included 1‐alkenes; acrylic, allyl and vinyl esters; and allyl and vinyl ethers. The bands caused by the vinyl structure were observed clearly and usually without interference. These bands consist of overtones of the fundamental C‐H stretching vitrations found in the normal IR region and of combination bands. Interactions between the vinyl group and the rest of the molecule were observed by changes in location, shape and intensity of the near IR bands. Quantitative analysis for vinyl derivatives based on near IR bands is usually convenient.

Spectroscopic study of derivatives of cyclo-pentadienylirondicarbonyl, containing an iron-tin bond

1. The IR spectra in the region of the frequencies of the valence vibrations of CO and the proton magnetic resonance spectra of a series of derivatives of cyclopentadienylirondicarbonyl, containing a tin-iron bond, were studied. 2. On the basis of the data obtained on the frequencies, relative intensities of the IR bands, and the values of the chemical shifts in the NMR spectrum, the mechanism of transmission of the influence of substituents on the tin atom to the carbonyl ligands and protons of the cyclopentadienyl ring, as well as possible conformations of derivatives of the type of [C5H5(CO)2Fe]2SnX2, are discussed.