Infrared spectra solvent effects

Local multipoles do not, therefore, interact with oscillating dipoles. They do, however, interact with and re-enforce permanent dipoles. The sign of the effect so generated on the infrared spectrum will depend on the particular case, and of course different modes wiU be affected differently. Particularly relevant is a study 47) carried out on Os(CO)4Br2 and Os(CO)4l2. In this, it was found that CO stretching frequencies increase, with increasing solvent multipole effect, in the order... 

Materials and Methods. The isomeric compositions of the four polybutadienes used are listed in Table I. Samples were prepared for infrared measurement from solutions of the polymer without further purification. Most films were cast from carbon disulfide solutions on mercury or on glass plates, but a few films were cast from hexane solutions to determine whether or not the solvent affected the radiation-induced behavior. No difference was observed for films cast from the different solvents. The films were cured by exposure to x-rays in vacuum. (Doses were below the level producing detectable radiation effects.) They were then mounted on aluminum frames for infrared measurements. The thicknesses of the films were controlled for desirable absorbance ranges and varied from 0.61 X 10 s to 2 X 10 3 cm. After measuring the infrared spectrum with a Perkin-Elmer 221 infrared spectrophotometer, the mounted films were evacuated to 3 microns and sealed in glass or quartz tubes (quartz tubes only were used for reactor irradiations). 

An interface between gel permeation chromatography (GPC) and Fourier transform infrared (FTIR) spectrometry has been developed. With this system it is possible to collect solvent free polymer deposition and to measure their infrared spectra as a function of molecular weight. The mobile phase from the GPC effluent is converted into an aerosol and removed using a pneumatic nozzle. The sample is collected on a Ge disc that rotates below the nozzle. After the sample is collected, the disc is transferred to an FTIR spectrometer where the infrared spectrum of the sample is collected. Normal GPC sample concentrations (0.1-0.25 wtJvol%) give sufficient sample for useable FTIR signals. All normal GPC solvents can be effectively removed, and the interface works with both low temperature and high temperature GPC applications. 

Repulsive Interactions (Harmonic Oscillator in a Box). In most stable solutions and in pure liquids where the components are at or near relatively deep intermolecular potential minima, attractive interactions dominate the intermo-lecular repulsive terms. Unstable solutions of large solute molecules dissolved in a solution of small solvent molecules can be prepared in the solid phase by trapping experiments. Certain trapped free radicals may therefore show the effects of solvent-solute repulsive interactions, which would be evidenced by blue shifts in the infrared spectrum of these cramped solutes. Diatomic carbon (C2) trapped in solid xenon shows this effect strongly (30, 31, 32) in both the upper and lower... 

Infrared and Raman Spectroscopy. Resonance Raman spectra of aW-trans- and 15-CW-/3-carotene have been compared.The ps resonance Raman spectrum of /8-carotene has been described,and solvent effects on the excitation profile of the line of jS-carotene have been studied. Model calculations have been used to interpret observed jS-carotene Raman spectra and excitation profiles. Raman scattering spectra of j8-carotene-l2 complexes have been determined. Resonance Raman spectra of carotenoids have been used as an intrinsic probe for membrane potential, e.g. neurosporene [7,8-dihydro-(/r,(/r-carotene (183)] in chromatophores of Rhodopseudomonas sphaeroides. ° Resonance Raman spectroscopy and i.r. spectroscopy have been used in studies of the chromophore of visual pigments and visual cycle intermediates and of bacteriorhodopsin and its photocycle intermediates. ... 

Carbon dioxide in water absorbs at 2343.5 cm" . The observed small shift for bound CO 2 was attributed to a solvent effect. The absence of a larger spectral shift showed that this substrate is not appreciably distorted upon binding by the enzyme. The data of Riepe and Wang (1968) indicated that at a pcoz of 1 and 25°C the active site of the enzyme was about 25% saturated with CO2. Consequently, the measurement of peak height from the difference infrared spectrum was much less reliable than the measurement of frequency for the bound COj. On the other hand, carbonic anhydrase can be completely saturated by azide at fairly low total con-concentration of the latter. Therefore, quantitative infrared measurements of the concentration of the enzyme-azide complex were more easily carried out. 

The solvatochrome effect may also appear in the infrared spectrum. The acceptor strength scale of Kagiya [Ka 68] is based on the solvent dependence of the C==0 vibration band for acetophenone. As for his donor strength scale, the reference solvent is benzene. The acceptor strength is denoted by the band shift,... 

In the past, solution-based measurements were popular mainly because sampling was limited to the simple procedures involving transmission measurements. One possible benefit is that both solids and liquids may be studied in solution. In this case, the optical effects caused by differences between these two types of sample phase are removed. The problem has always been the selection of an appropriate solvent. All liquids have an infrared spectrum, and almost all liquids have relatively intense and complex spectra. There are few materials that have simple spectra that have clear windows for broad-range transmission measurements. As a general comment, the materials that are the best solvents, particularly for polar compounds, by nature are strong infrared absorbers. Therefore, it is very difficult to find convenient solvents that have good solvent characterisitics, that are relatively involatile, and that are convenient to handle (e.g., are nontoxic). 

E. N. Vasenko, Effect of the Solvent on the Position of the Absorption Rands in the Infrared Spectrum of Amides, Fix. Sbornik Uvav. Univ. 1957, No. 3, 192-195. 

The carbon monoxide present in the solution may also react with the products or the coordinatively unsaturated species, effectively reversing the reaction 137, 138). The differences in the behavior of the three carbonyls and the effect of solvent have been noted, so that one may choose the proper conditions for obtaining the desired product 137, 138, 139). For hexa-carbonylchromium and -tungsten, the order of reactivity of donors is pyridine > tetrahydrofuran > triethylamine > acetonitrile > 1,3-cyclohexa-diene > ethyl acetate > acetone > tolane. In the case of hexacarbonyl-molybdenum, acetonitrile and tolane are advanced in the series 138). Other workers have studied the photochemical reaction of [Mo(CO)6] with nitriles 107). The infrared spectrum of irradiated hexacarbonylmetal glasses at -180° C indicates the presence of the (tetragonal pyramidal)... 

---