Solvent Effects on Infrared Spectra

The measurement of such solvent-induced IR spectral changes has been extensively used in spectroscopic studies of solute/solvent interactions [1-4, 367], especially 

The wavenumber displacement of a solute vibration is a complex function of both solute and solvent properties and can be explained in terms of weak nonspecific electrostatic interactions (dipole-dipole, dipole-induced dipole, etc.) and of strong specific association of solute with solvent molecules, usually of the hydrogen-bond type [140], It should be realized that the duration of vibrational transitions is very short with respect to motion of the solvent molecules e.g. for an O—H stretching vibration, the frequency is ca. 10 s ). Thus, it is possible to observe such transitions even for short-lived entities such as may arise after a collision in the liquid phase (collision complexes) [140], 

To a first approximation, the bathochromic shift observed for the C=0 stretching vibration of acetone [cf. Table 6-4) in non-HBD solvents may be explained by the degree of C=0 dipolarity as determined by the relative contribution of the two meso-meric forms in Eq. (6-6). 

A change in the external environment produces small alterations in the relative contribution of the two mesomeric structures, and affects the wavenumbers of absorption in much the same way as do changes in the internal chemical environment [146], Accordingly, the vc-o absorption band of acetone is displaced from 1721.5 cm in 

The differentiation between effects due to specific solute/solvent interactions and bulk dielectric solvent effects is not easy to visualize and is often a matter of debate [367]. The experimental data indicate that the solvent sensitivities of vx-o vibrations are complex functions of several factors, including contributions from bulk dielectric effects, non-specific dispersion and induction forces, specific HBD/HBA interactions, as well as steric effects [134]. Solvent effects on the vc o IR stretching absorption have been line- 

---

Liu, Q., Sang, W., and Xu, X., Solvent effects on infrared spectra of 5-methyl-7-methoxy-iso-flavone in single solvent systems, J. Mol. Struct., 608, 253, 2002. 

Energy Relationships. 1. Solvent Polarity-Polarizability Effects on Infrared Spectra. 

Kamlet, M.J. and Taft, R.W. (1979b). Linear Solvation Energy Relationships. Part 1. Solvent Polarity-Polarizability Effects on Infrared Spectra. J.Chem.Soc.Perkin Trans.2,337-341. 

There are many more solvent effects on spectroscopic quantities, that cannot be even briefly discussed here, and more specialized works on solvent effects should be consulted. These solvent effects include effects on the line shape and particularly line width of the nuclear magnetic resonance signals and their spin-spin coupling constants, solvent effects on electron spin resonance (ESR) spectra, on circular dichroism (CD) and optical rotatory dispersion (ORD), on vibrational line shapes in both the infrared and the UV/visible spectral ranges, among others. 

The solvent effect on the uv/vis absorption spectra and the infrared and H NMR spectral data of (V-(nitrophenyl)alkylenediamines 82 and 83 shows spectroscopic behaviour, indicating the presence of an intramolecular hydrogen bond between the amino groups (cf. Scheme 17) which compete with the intermolecular hydrogen bond between 82 and 83 and the solvents150. 

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. ... 

Dyall, L.K. (1969) Solvent effects on the infrared spectra of anilines. V. Anilines with no ortho substituents. Spectrochim. Acta, Part A, 25, 1423-1435. 

Figure 17. The effect of cyclohexane (A) and dichloromethane (B) solvents on the desorption of cinchonidine (abbreviated as CD) from platinum [66], In both cases, a clean platinum surface was first exposed to a cinchonidine solution in CC14 to allow for the adsorption of cinchonidine, and the platinum disk was then exposed to either cyclohexane or dichloromethane. In the case of cyclohexane, a total rinsing with 180 mL in several sequential flushings did not lead to significant change of the infrared spectra. On the other hand, with dichloromethane (B), one flush was sufficient to remove most of the adsorbate. [Reproduced by permission of the American Chemical Society from Ma, Z. Zaera, F. J. Phys. Chem. B 2005,109, 406-414.]...

IR spectra were obtained on a Model 10MX Nicolet Fourier Transform infrared spectrometer. IR films were spin-coated from polymer solutions in chlorobenzene on either KBr discs or silicon wafers polished on both sides. The samples were baked in vacuum at 90 C for at least 1 hour to ensure solvent removal. Film thicknesses were approximately 1 jtm, sufficient to remove interference fringe effects from the spectra. 

Another consequence of the strong absorption properties of water is the spectral impact of the displacement of water by dissolved solutes. Generally, in absorption spectroscopy, the solvent is selected not to absorb over the wavelength range of interest. When the absorption properties of the solvent are negligible, any displacement of solvent molecules from the optical path by the dissolution of solute molecules has a negligible effect on the measured spectrum. For near-infrared spectra of aqueous solutions, however, the absorption spectrum depends heavily on the degree of water displacement by solutes in the sample. 

A number of studies have been made of the solvent dependence of the infrared spectra of carbonyl compounds. The results have shown that to a limited extent this effect can be used to aid assignment of CO-stretching fundamentals. Quantitative measurements of the variations on frequency and half-band widths vn2 with changing solvents have been made, but as yet, the solvent dependence of the intensities has not been studied in detail. 

---