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 attenuation 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' versus frequency shows two domains: the microwave frequency range previously studied and interpreted as the rotational relaxation of the methoxy groups, -OCH3, around the carbonyl moiety, > C = 0, and a new domain 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 reveals 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 of CCl4 and DMC because of interactions in the former pair arising from H bonding. Mixtures of DMC and CHCl3 have a microwave dielectric spectrum that differs markedly from that which would be expected for mole fraction X(DMC) = 0.50, if the two components did not interact strongly with each other. The dielectric relaxation frequencies of pure DMC and pure CHCl3 are f(r) = 22 and 27 GHz, respectively. When they are mixed at a composition X(DMC) = 0.50, a dielectric relaxation spectrum is produced that can be interpreted by a Cole-Cole distribution with an average relaxation frequency f(r) = 17 GHz and a distribution relaxation parameter alpha = 0.08 (0 < alpha < 1 with alpha = 0 for a single Debye relaxation process). This microwave dielectric relaxation is ascribed to the formation of H-bonded complexes arising from interactions of the proton of CHC13 and the carbonyl moiety of DMC. A similar X(DMC) = 0.50 mixture of DMC and CCl4 does not produce the same microwave dielectric relaxation thus supporting the attribution of the phenomenon 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 arising from hydrogen bonding between EC and CHCl3.