MICROWAVE AND INFRARED DIELECTRIC-RELAXATION OF ALKYL CARBONATES, CHLOROFORM, AND THEIR MIXTURES AT 25-DEGREES-C

Microwave data yielding the complex permittivity epsilon' - epsilon' - Jepsilon'', infrared and visible refractive indices, and infrared att enuation coefficients for liquid dimethyl carbonate [(CH3O)2CO; abbrev :DMC], chloroform, and their mixtures have been recorded at 25-degrees -C. For pure DMC the real part of the complex permittivity epsilon' ve rsus frequency shows two domains: the microwave frequency range previo usly studied and interpreted as the rotational relaxation of the metho xy groups, -OCH3, around the carbonyl moiety, > C = 0, and a new domai n at infrared frequencies. This latter domain showing a decay of n2 is probably attributable to intramolecular vibrations. The profile of n( IR2) (the squared refractive index) versus frequency for pure CHCl3 re veals a dielectric phenomenon hinted at by literature data obtained at far-IR frequencies. This phenomenon can be explained qualitatively as due to weakly damped resonance absorptions. Mixtures of CHCl3 and DMC are more interesting in the microwave frequency range than mixtures o f CCl4 and DMC because of interactions in the former pair arising from H bonding. Mixtures of DMC and CHCl3 have a microwave dielectric spec trum that differs markedly from that which would be expected for mole fraction X(DMC) = 0.50, if the two components did not interact strongl y with each other. The dielectric relaxation frequencies of pure DMC a nd pure CHCl3 are f(r) = 22 and 27 GHz, respectively. When they are mi xed at a composition X(DMC) = 0.50, a dielectric relaxation spectrum i s produced that can be interpreted by a Cole-Cole distribution with an average relaxation frequency f(r) = 17 GHz and a distribution relaxat ion parameter alpha = 0.08 (0 < alpha < 1 with alpha = 0 for a single Debye relaxation process). This microwave dielectric relaxation is asc ribed to the formation of H-bonded complexes arising from interactions of the proton of CHC13 and the carbonyl moiety of DMC. A similar X(DM C) = 0.50 mixture of DMC and CCl4 does not produce the same microwave dielectric relaxation thus supporting the attribution of the phenomeno n to the formation of a hydrogen-bonded CHCl3-DMC complex. Mixtures of ethylene carbonate [EC] and CHCl3 UP to CEC congruent-to 3 M produce a microwave dielectric spectrum that can also be interpreted as arisin g from hydrogen bonding between EC and CHCl3.