Molekülinterne Dipolorientierung und dielektrische Absorption in verdünnter Lösung bei Mikro-und Submillimeterwellen. V.Acetyl-Verbindungen

The dielectric loss of sixteen molecules, eleven with the acetyle group in aromatic bonds and five in aliphatic bonds, has been measured in very dilute solutions of cyclohexene at 20 °C. Five of these molecules are investigated in decalene solutions, too. The measurements have been made at wavenumbers in the range 0.08 to 140 cm -1 above 8 cm -1 making use of a pumped molecular laser. They are supplemented by the data of a Fourier transform spectrometer up to 300 cm -1. All microwave spectra of loss factor ε″ are analysed in terms of three absorption areas using the two variable Mori formalism. On the other hand, Lorentz curves are fitted to the FIR absorption spectra of α(v̄).The fast relaxation process of the aliphatic compounds is suggested to be due to intramolecular reorientation of the acetyle group itself, since in acetyle cyclohexene the remaining part of the molecule is rigid. To the contrary, the acetyle group is not able to reorientate swiftly, if bounded to aromatic rings. Presumably, it is fixed by mesomeric interaction with the dipole in the plain of the ring. However, 2-methyl acetophenone and 1-acetyle naphthone show some quick dipole reorientation, which coincides with a steric hindrance of the group in entering the plain of the ring.