Solvent effects in infra-red spectra: C=O, C-H, and C-C vibrations

Abstract

Frequency displacements and intensities are reported for the C=O stretching fundamental and first overtone in acetone, acetaldehyde, and diisopropyl ketone, for the chloroform C-H stretching fundamental, and for the acetonitrile C-C stretching fundamental, all in a variety of non-polar and polar solvents. The solvent displacement of C-C is very small (?1 K), for C-H and C=O it is to the red and of the order of 10-20 K, with C=O overtones being displaced about twice as much as the fundamentals. The Kirkwood relation between the frequency displacement and solvent dielectric constant is inadequate if the static D is used. The C=O results can be. interpreted in terms of two superimposed effects : (i) the electronic polarization of the solvent causes a frequency shift related to the solvent refractive index, and (ii) in polar solvents there is an additional shift due to solvent dipole orientation. Effect (ii) causes an added contribution to the intensity. The C-H results do not fit easily into this interpretation.

Linear Free Energy Relationships.

“…Although the quantitative aspects of solvent effects on a number of physical properties, such as refractive index (9) and infrared frequencies (17,19), have been examined, successful correlations have only been achieved for shifts in ultraviolet and visible spectra. These have, however, such an exceptional precision that it is suggested (46,154,155,156) that these measurements provide an independent and accurate means of determining solvent parameters.…”

“…3 0 3 R T~ (8) log ( k i / k~)~ = gzB(zo -zi)/2.303RT~ (9) where k represents a rate or equilibrium constant, and the g-terms are the partial differentials of a standard free-energy of activation or a standard free-energy change during reaction as appropriate.…”

Solvent effects in infra-red spectroscopy

“…(5-6) I t is clear th a t (5-3) has m uch m ore scope for fitting experim ental d a ta th a n (IT ), w hich is know n to be in adequate in m any cases. Thus th e conclusion (Bayliss et al 1955) th a t a value of e less th a n th e sta tic value of th e dielectric co n stan t of a polar solvent, b u t nevertheless g reater th a n n 2, is indicat to experim ental d a ta is supported strongly b y (5-3). As a p ractical m ethod of correlating small observed shifts, (5-3) could be sim plified so th a t in polar m edia (5-7)…”

Infrared study on the interaction of poly(vinyl chloride) and ketones

“…Nonpolymeric systems containing chlorinated hydrocarbons and ketones show interactions. These were observed, for example, in dilute solutions of ketones in carbon tetrachloride (4-7), chloroform (4,8,9), deuterated chloroform (7,9), methylene chloride (4), dichloroethane (4), and tetrachloroethane (4). The carbonyl absorption shifts to lower frequencies except for carbon tetrachloride, which shows the opposite displacement taking as reference the absorption of the corresponding ketone as liquid film (5).…”