Infrared Band Contours Research Articles

Infrared Spectrometric and Liquid Chromatographic Studies of Cyanoalkyl- Bonded Phases: A Competitive Two-Site Adsorption Model

Fourier transform infrared techniques and high performance liquid chromatography are used to study solvent-surface and solute-surface interactions for 3-cyanopropyl—modified silica in binary mixtures of 1-butanol and hexane. Plots of log k′ vs. mobile phase composition are either linear or biphasic depending on the test solute's appended functionality. These data as well as changes in the infrared band contour of the nitrile stretch region suggest a competitive two-site two-state displacement model.

Vinyl formate in the gas phase, investigated by electron diffraction, microwave spectroscopy and infrared band contour analysis, supplemented with molecular mechanics and ab-initio calculations of geometries and force fields

The structure of vinyl formate was studied by joint analysis of gas phase electron diffraction, microwave and infrared data including band profiles. The experimental data were supplemented with vibrational constraints taken from force field calculations on the 4–21G ab initio level, and with geometrical constraints arising from molecular mechanics (MM2 force field), STO-3G and geometry-relaxed 4–21G ab initio calculations. All data are in accord with a planar heavy-atom skeleton in the ( sp, ap) conformation, i.e. torsion angle φ(OCOC) = 0° and φ(CCOC) = 180°. From the occurrence of a single form at room temperature, it follows that ( sp, ap) is at least 2.3 kcal mol −1 more stable than the next conformer. Geometry constrained models based on MM2 and the STO-3G constraints were rejected on statistical grounds. The analysis favours the 4–21G constrained models. Subject to the ab initio constraints, the following internal coordinates ( r g -distances, r 0 α-angles) were found: CC, 1.331 Å; (C)CO, 1.397 Å; (O)CO, 1.350 Å; CO, 1.193 Å; CH, 1.087 Å; CCO, 121.0°: COC, 117.0°; OCO 127.2°.

Vibrational spectra of cyclopropyl cyanide and cyclopropyl cyanide‐α‐d1

AbstractRaman spectra of cyclopropyl cyanide‐α‐d1 (CPCN‐d) in its condensed phases have been recorded for the first time, along with the solid‐phase Raman spectrum of the parent compound, cyclopropyl cyanide (CPCN). In addition, liquid‐ and solid‐phase infrared spectra were obtained for the isotopic derivative, and gas‐phase Fourier transform infrared spectra were obtained for both compounds. The data for CPCN‐d, combined with information deduced from gas‐phase infrared band contours and Raman depolarization ratios, enable vibrational assignments to be proposed for 47 of the 48 normal modes of these two molecules. Strong mixing of several modes in CPCN is revealed by the deuterium labeling, and evidenc for self‐association in the condensed phases is discussed. The vibrational frequencies and assignments are compared with similar results for other cyanide‐ and halogen‐substituted cyclopropanes.

Spectra and structure of organophosphorus compounds. XXV—Raman and infrared spectra and conformational stability of ethyldimethylphosphine

AbstractThe Raman (10–3500 cm−1) and infrared (50–3500 cm−1) spectra have been recorded for gaseous and solid ethyldimethylphosphine, CH3CH2P(CH3)2. Additionally, the Raman spectrum of the liquid has been recorded and qualitative depolarization values have been obtained. From the fact that several distinct Raman lines disappear on going from the fluid phases to the solid state, it is concluded that the molecule exists as a mixture of the gauche and trans conformers in the fluid phase with the gauche conformer being more stable and the only one present in the spectrum of the solid. From a temperature study of the Raman spectrum of the liquid, the enthalpy difference between the gauche and trans conformers was determined to be 134 ± 32 cm−1 (383 ± 92 cal mol−1). Relying on group frequencies and relative intensities of the infrared and Raman bands, and in some cases infrared band contours, a complete vibrational assignment is proposed for the gauche conformer. The assignment is supported by a normal coordinate calculation which was carried out utilizing a modified valence force field to obtain the frequencies of the normal modes and the potential energy distribution. The CH3‐P torsions have been observed at 208 and 185 cm−1 in the gas phase and from these frequencies the periodic barriers to internal rotation have been calculated to be 905 ± 95 cm−1 (2.56 kcal mol−1). The CH3‐C torsion was also observed in the gas phase at 217 cm−1 from which a periodic barrier of 1134 cm−1 (3.22 kcal mol−1) was calculated. The asymmetric torsional mode has been observed for the gauche conformer in both the infrared and Raman spectra of the gas at 91 cm−1 with evidence of ‘hot bands’ at lower frequencies. All of these results are compared with corresponding quantities for several other organophosphines.

Spectra and structure of organogermanes. XXII. Microwave, infrared, and Raman spectra of methylgermyl cyanide

The microwave spectra have been recorded from 18.0 to 26.5 GHz for 12CH3GeH212C14N, 13CH3GeH212C14N, 12CH3GeH212C15N, 12CH3GeH213C14N, 12CH3GeD212C14N, and 12CD3GeH212C14N of the four naturally occurring isotopes of germane: 70Ge, 72Ge, 74Ge, and 76Ge. Only a-type transitions were observed and R-branch assignments have been made for all the isotopic species in the ground vibrational state from which the rotational constants were determined. From these data the complete structural parameters were determined to be r0(CME–Ge)=1.933±0.002 Å, r(Ge–CCN)=1.927±0.004 Å, r(C≡N)=1.155±0.004 Å, r(Ge–H)=1.521±0.001 Å, r(C–Hs)=1.092±0.005 Å, r(C–Ha)=1.092±0.005 Å, ∢CGeC=107.36°±0.60°, ∢HGeH=111.41°±0.04°, ∢HGeCMe=112.92°±0.08°, ∢HsCGe=109.5°±2.0°, and <HaCGe=109.3°±0.8°, where all of the parameters are rs values except for the carbon–hydrogen distances and angles. The dipole moment components were determined from the Stark effect to be ‖μa‖=4.20±0.14, ‖μb‖=0.39±0.03, and ‖μt‖=4.22±0.14 D. From the microwave splitting method, the threefold barrier to internal rotation was determined to be 1148±23 cal/mol (402±8 cm−1). The infrared (3200 to 50 cm−1) and Raman spectra (3200 to 10 cm−1) of gaseous and solid CH3GeH2CN, CH3GeD2CN, and CD3GeH2CN have been obtained. Additionally, the Raman spectra of the liquids have been recorded and qualitative depolarization values have been obtained. A complete vibrational assignment is proposed based on infrared band contours, depolarization values, and isotopic shifts. These results are compared to similar quantities in some related molecules.

Spectra and structure of small ring molecules: Part XLIV. Vibrational spectra and conformational stability of cyclobutylmethyl ketone

The infrared (3500 to 30 cm −1) and Raman (3200 to 30 cm −1 spectra have been recorded for the gaseous and solid states of cyclobutylmethyl ketone, c-C 4H 7C(CH 3)O. Additionally, the Raman spectrum of the liquid has been recorded and qualitative depolarization values have been obtained. Evidence is presented based on the band contours in the infrared spectrum that the molecule exists predominantly in the equatorial- gauche conformation (the C(CH 3)O group is in the equatorial position relative to the four-membered ring with the CO nearly eclipsing one of the CC bonds of the ring) in the gaseous and liquid states and exclusively in this conformation in the solid state. However, there is clear evidence in the Raman spectra of the fluid phases that a second conformer is present at ambient temperature and this conformer is believed to be the equatorial- trans where the CO is eclipsing the α-CH bond of the four-membered ring. The asymmetric torsion was observed as a very broad, structureless band centered at about 51 cm −1. From the relative intensities of the Raman lines of the liquid at 386 (equatorial- gauche) and 442 cm −1 (equatorial- trans) as a function of temperature, the enthalpy difference was found to be 480 ± 62 cm −1 (1.37 kcal mol −1) with the equatorial- gauche being more stable. A complete vibrational assignment is proposed based on infrared band contours, depolarization values, and group frequencies. The methyl torsion was tentatively assigned at 112 cm −1 from which a threefold barrier to internal rotation was calculated to have a value of 0.94 kcal mol −1 (331 cm −1). A few of the normal modes were observed to be split in the infrared spectrum of the solid which indicates that there are at least two molecules per primitive cell. These results are compared to similar quantities in some related molecules.

Low resolution microwave, infrared and Raman spectra, conformational stability, and vibrational assignment of isopropylisothiocyanate

The low resolution microwave spectrum of isopropylisothiocyanate, (CH 3 2CHNCS, has been recorded from 18.0 to 39.0 GHz. From the spacing of the central transitions for the near prolate symmetric top it is shown that the value of 2490 MHz for B+C is consistent with the skew conformer with a CNC angle of ≈ 145° where the NCS moiety is eclipsing one of the methyl groups, although the trans conformer where the lone pair of electrons on the nitrogen is eclipsing the hydrogen atom cannot be completely ruled out. The infrared and Raman (3200—30 cm −1 spectra of gaseous and solid isopropylisothiocyanate have been recorded. Also, the infrared spectrum of the sample isolated in a nitrogen matrix at 10 K has been recorded from 3200 to 300 cm −1. Additionally, the Raman spectrum of the liquid has been obtained and qualitative depolarization values measured. Based on a comparison of the vibrational data for the fluid and solid phases it has been determined that there is little evidence for the presence of a second conformer at ambient temperature and there was no evidence for the presence of two conformers in the matrix isolated sample. A complete vibrational analysis, based on infrared band contours, depolarization values and group frequencies, is proposed. The two methyl torsions were observed in the Raman spectrum of the solid at 285 and 250 cm −1 and from these data the barrier to internal rotation was calculated to be 1640 cm −1 (4.69 kcal mol −1). Additionally, a very weak B-type band centered at ≈45 cm −1 was observed in the infrared spectrum of the gas which probably arises from the asymmetric torsion of the NCS moiety. These results are compared to similar quantities for some corresponding molecules.

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.

Infrared and Raman spectra of cyclopropane-1,1- d2 and cyclopropane-1,1,2,2- d4

Vapor phase infrared and liquid Raman spectra of cyclopropane- 1,1- d 2 and cyclopropane- 1, 1,2,2- d 4 with vibrational assignments are presented. Close agreement is found between observed fundamental frequencies and those calculated from the cyclopropane force field of B lom and A ltona. Observed and calculated vapor phase infrared band contours for these cyclopropane isotopic molecules at 0.5 cm − resolution are compared. Infrared and Raman spectra for pure polycrystailine cyclopropane-1,1- d 2 and cyclopropane- 1,1,2,2- d 4, as well as for dilute solid solutions of each of these molecules, are presented.

ChemInform Abstract: VIBRATIONAL SPECTRUM AND CONFORMATION OF 2‐METHYL‐2‐NITROPROPANE

Abstract The infrared spectra of gaseous and solid 2-methyl-2-nitropropane, (CH 3 ) 3 CNO 3 , have been recorded from 25 to 3500 cm −1 and 80 to 3500 cm −1 , respectively. The Raman spectra of gaseous, liquid and solid 2-methyl-2-nitropropane have been recorded from 20 to 3500 cm −1 and depolarization values have been obtained for the liquid. A complete vibrational assignment for all of the normal modes based on band contours, depolarization values, and group frequencies has been made except for the NO 2 torsion. The vibrational data are consistent with the molecule either being in the bisected conformation or having essentially free internal rotation of the NO 2 group in the fluid phases. Taking into consideration all the available data from the vibrational and rotational spectra, it is probable that the nearly free internal rotation ( V 6 = 71 cm −1 ) can best explain the observed depolarization values, the diffuse infrared band contour for the NO 2 wag, and the far infrared spectrum of the gas. However, from a CNDO/2 calculation, the bisected conformation was found to be more stable than the eclipsed form by 176 cal mol −1 , which is consistent with the Raman depolarization data. From the frequencies for the methyl torsional modes which have been observed in the spectra of the solid phase, a barrier to internal rotation of the methyl groups of 3.93 kcal mol −1 has been calculated. The spectra of the solid are consistent with two molecules per primitive cell. These results are compared to the corresponding quantities for some similar molecules.

Vibrational spectrum and conformation of 2-methyl-2-nitropropane

The infrared spectra of gaseous and solid 2-methyl-2-nitropropane, (CH 3) 3CNO 3, have been recorded from 25 to 3500 cm −1 and 80 to 3500 cm −1, respectively. The Raman spectra of gaseous, liquid and solid 2-methyl-2-nitropropane have been recorded from 20 to 3500 cm −1 and depolarization values have been obtained for the liquid. A complete vibrational assignment for all of the normal modes based on band contours, depolarization values, and group frequencies has been made except for the NO 2 torsion. The vibrational data are consistent with the molecule either being in the bisected conformation or having essentially free internal rotation of the NO 2 group in the fluid phases. Taking into consideration all the available data from the vibrational and rotational spectra, it is probable that the nearly free internal rotation ( V 6 = 71 cm −1) can best explain the observed depolarization values, the diffuse infrared band contour for the NO 2 wag, and the far infrared spectrum of the gas. However, from a CNDO/2 calculation, the bisected conformation was found to be more stable than the eclipsed form by 176 cal mol −1, which is consistent with the Raman depolarization data. From the frequencies for the methyl torsional modes which have been observed in the spectra of the solid phase, a barrier to internal rotation of the methyl groups of 3.93 kcal mol −1 has been calculated. The spectra of the solid are consistent with two molecules per primitive cell. These results are compared to the corresponding quantities for some similar molecules.

Infrared and Raman spectra and normal coordinate calculations for methylisothiocyanate

The infrared spectra (3200-50 cm −1) of gaseous and solid CH 3NCS and CD 3NCS and the Raman spectra (3200-10 cm −1) of the liquids and solids have been recorded. The spectra have been interpreted on the basis of a “pseudo-symmetric top” with C 3v symmetry. An assignment of the fundamental vibrations in both molecules, based on their infrared band contours, depolarization values and group frequencies, is given and discussed. Particularly interesting is the low-frequency region where band maxima were observed at 152 and 80 cm −1 for CH 3NCS and 139 and 71 cm −1 for CD 3NCS in the infrared spectra of the gases. A normal coordinate analysis has also been carried out based on C 3v symmetry. Considerable mixing was found between the C αN stretch and NCS symmetric stretch in both isotopic species. The other normal modes in CH 3NCS are reasonably pure but, for the CD 3NCS molecule, considerable mixing was found between the CD 3 stretches and NCS antisymmetric stretch. The proposed vibrational assignment and the results of the normal coordinate calculations are discussed and compared with the results obtained for similar molecules.

Vibrational and conformational studies of cyclopropylcarbonyl chloride

The infrared (3500 to 20 cm −1) and Raman (3200 to 10 cm −1) spectra have been recorded for gaseous and solid cyclopropylcarbonyl chloride, c-C 3H 5CClO. Additionally, the Raman spectrum of the liquid has been recorded and qualitative depolarization values have been obtained. It has been determined that the conformer with the oxygen atom cis to the three-membered ring is the predominant form at ambient temperature in both the gaseous and liquid states but only the trans conformer is present in the spectra of the solid. From a temperature study of the Raman spectrum of the liquid an energy difference of 93 ± 20 cm −1 (267 cal mol −1) has been determined whereas the energy difference for the gaseous state was determined to be 297 ± 10 cm −1 (849 cal mol −1) from the infrared spectrum. The observed changes in Δ H in going from the gas to the liquid state indicates strong intermolecular association in the condensed phases which can account for the existence of the trans conformer in the solid state. The torsional mode has been tentatively assigned at 72 cm −1 in the far infrared spectrum of the vapor for the cis conformer, and for the trans conformer at ∼50 cm −1. From these frequencies and the Δ H for the gas, estimates are given for the values of the coefficients of the Fourier expansion of the potential function for internal rotation. The number of lattice modes observed in the infrared and Raman spectra of the solid indicates at least two molecules per primitive cell. A complete vibrational assignment is proposed for both conformers based on infrared band contours, depolarization values, and group frequencies. These results are compared to similar quantities in some related molecules.

Microwave, infrared and Raman spectra, conformation, and vibrational assignment of isopropylisocyanate

The low resolution microwave spectrum of isopropylisocyanate, (CH 3) 2CHNCO, has been recorded from 18.0 to 39.0 GHz. From the spacing of the major transitions it is shown that the value of 4031 MHz for B + C is consistent with the skew conformer with a CNC angle of ca. 139° where the NCO moiety is eclipsing one of the methyl groups, although the trans conformer where the lone pair of electrons on the nitrogen is eclipsing the hydrogen atom cannot be entirely ruled out. The infrared (3200-50 cm −1) and the Raman (3300-20 cm −1) spectra have been recorded for gaseous and solid isopropylisocyanate. Additionally, the Raman spectrum of the liquid has been obtained and qualitative depolarization values measured. There is little indication of the presence of a second conformer at ambient temperature from a comparison of the vibrational data for the fluid and solid phases. A complete vibrational analysis, based on infrared band contours, depolarization values and group frequencies, is proposed. The two methyl torsions have been observed in the Raman spectrum of the solid at 278 and 257 cm −1 and from these data the barrier to internal rotation was calculated to be 1620 cm −1 (4.63 kcal mol −1). These results are compared with similar quantities for some corresponding molecules.

Conformational barriers to internal rotation and vibrational assignment of cyclopropylcarbonyl fluoride

The infrared (3500 to 50 cm−1) and Raman (3200 to 10 cm−1) spectra have been recorded for the gaseous and solid states of cyclopropylcarbonyl fluoride, c-C3H5CFO. Additionally, the Raman spectrum of the liquid has been recorded and qualitative depolarization values have been obtained. The asymmetric torsion for the conformer which has the carbonyl group cis to the cyclopropane ring has been observed at 88.5 cm−1 in the far infrared spectrum of the gas with five accompanying hot bands, and the corresponding torsion of the trans conformer was observed at 91.0 cm−1 with two additional hot bands occurring at 90.6 and 90.2 cm−1. From these data the potential function for internal rotation of the asymmetric top has been determined and the following potential constants have been evaluated: V1=−618±6, V2=1970±27, V3=399±6, and V4=−48±10 cm−1. It has been determined that the cis conformer is the predominant form at ambient temperature in the gas phase and the enthalpy difference between the cis and the trans conformers is 222 cm−1 (629 cal/mol) for the vapor. The calculated trans-cis barrier is 1948 cm−1 (5.57 kcal/mol) and the cis-trans barrier is 2168 cm−1 (6.20 kcal/mol). From a temperature study of the Raman spectrum of the liquid an energy difference of 92±20 cm−1 (263 cal/mol) has been determined with the trans conformer being more stable in the liquid phase due to intermolecular interactions. Additionally, an investigation of the vibrational spectrum of the solid state indicates that both conformers persist even to 30 K but the trans conformer is more stable. The number of lattice modes observed in the Raman spectrum of the solid indicates at least two molecules per primitive cell. A complete vibrational assignment is proposed based on infrared band contours, depolarization values, and group frequencies. These results are compared to similar quantities in some related molecules.

Raman and infrared spectra, vibrational assignments and barriers to internal rotation of cis‐ and trans‐1‐chloropropene

AbstractThe Raman spectra of both cis‐ and trans‐1‐chloropropene were obtained between 3500 and 20 cm−1 for the vapor, liquid and solid states and the polarization data were obtained for the fluid phases. The infrared spectra were recorded between 3500 and 50 cm−1 for both compounds in the vapor and solid states. Complete vibrational assignments based on depolarization data, infrared band contours and group frequencies are presented for both molecules on the basis of Cs symmetry. The methyl torsion for trans‐1‐chloropropene was observed in the infrared spectrum of the vapor as a series of transitions with the 1 ← 0 fundamental having a frequency of 208 cm−1; from this fundamental frequency a periodic barrier to internal rotation was calculated to be 844±16 cm−1 (2413±46 cal mol−1). Although the methyl torsion was not observed directly for cis‐1‐chloropropene, the first overtone was tentatively assigned in the Raman spectrum of the vapor at 205 cm−1. Many of the fundamentals for both the cis and trans molecule appear as doublets in the spectra of the solids which indicates that there are at least two molecules per primitive cell for each solid. These results are compared to corresponding quantities in some similar molecules.

The millimeter-wave spectrum of CF 3Cl

The rotational spectra of CF 3 35Cl and CF 3 37Cl in their ground vibrational states were recorded in the microwave and millimeter-wave region, and analyzed to give precise values of the B rotational constants, centrifugal distortion constants, and quadrupole coupling constants. In addition, rotational spectra for the doubly degenerate states v 5 = 1 and v 6 = 1 of CF 3 35Cl were analyzed to yield values of ζ 5 and ζ 6. These are in good agreement with those obtained from Raman and infrared band contour analysis.

Microwave, infrared and Raman spectra, conformational stability and vibrational assignment of methoxyflurane

The low resolution microwave spectrum of methoxyflurane, CHCl 2CF 2OCH 3, has been recorded from 26.5 to 39.0 GHz. From the spacing of the major transitions it is shown that the value of 2036 MHz for B + C is consistent with the trans-trans or gauche-trans conformers where the first term ( trans or gauche) refers to the internal rotation around the C-C bond. The infrared (40–3500 cm −1) and the Raman (20–3500 cm −1) spectra have been recorded for gaseous and solid methoxyflurane. Additionally, the Raman spectrum of the liquid has been obtained and qualitative depolarization ratios measured. From these data it is shown that the most stable form in the fluid phases at ambient temperature is the gauche-trans conformer but the trans-trans form is the most stable in the solid state. A complete vibrational analysis based on infrared band contours, depolarization values and group frequencies is proposed for this conformer. From the analysis of the low frequency vibrational data, values of some of the barriers to internal rotation are estimated. These results are compared to some similar quantities for some corresponding molecules.

Vibrational spectra and conformation of oxalyl chlorofluoride in the crystalline and fluid states

The infrared (2000-20 cm −1) spectra have been recorded for gaseous and solid oxalyl chlorofluoride and the Raman (2000-10 cm −1) spectra obtained for the liquid and solid. Qualitative depolarization values have been obtained for the liquid. From these data it is shown that a second conformer of oxalyl chlorofluoride exists in the fluid phases and it is probable that it is the cis conformer but the gauche form cannot be ruled out completely. Attempts to obtain the enthalpy difference between the two conformers were unsuccessful. A complete vibrational assignment for trons-oxalyl chlorofluoride which is the most stable conformer is proposed based on infrared band contours, depolarization values and group frequencies. The torsional mode was observed at 38 cm −1in the infrared spectrum of the gas. Several of the fundamentals appeared as doublets in the infrared and Raman spectra of the solid which indicates that there are at least two molecules per primitive cell. These results are compared to similar quantities in related molecules.

Conformational barriers to internal rotation and vibrational assignment of methyl vinyl ketone

The infrared (3500 to 50 cm−1) and Raman (3200 to 10 cm−1) spectra have been recorded for the gaseous and solid states of methyl vinyl ketone. Additionally, the Raman spectrum of the liquid has been recorded and qualitative depolarization values have been obtained. The asymmetric torsion for the s-trans conformer was observed at 116 cm−1 in the infrared spectrum of the gas with two accompanying hot bands and the corresponding torsion of the s-cis conformer was observed at 87 cm−1 with an additional hot band occurring at 84 cm−1. From these data the potential function for internal rotation of the asymmetric top has been determined and the following potential constants have been evaluated: V1 = 180±9, V2 = 827±107, V3 = 113±8, and V4 = 150±34 cm−1. From these data it has been determined that the s-trans conformer is the predominant form at ambient temperature and the enthalpy difference between the s-trans and s-cis conformers is 280 cm−1 (800 cal/mol) for the vapor. The calculated trans–cis barrier is 827 cm−1 (2.36 kcal/mol) and the cis–trans barrier is 547 cm−1 (1.56 kcal/mol). From the relative intensities of the Raman lines of the liquid at 607 (s-cis) and 537 cm−1 (s-trans) as a function of temperature, the enthalpy difference was found to be 172 cm−1 (492 cal/mol). A complete vibrational assignment is proposed based on infrared band contours, depolarization values, and group frequencies. These results are compared to similar quantities in related molecules.