Studies on Molecular Structure by the Measurement of the Dielectric Constants of Gases and Vapors. I. Construction of an Apparatus and the Dipole Moment and the Molecular Structure of 1, 1-Dichloroacetone

An apparatus for the measurement of dielectric constant in the gaseous state is constructed. The electrical circuit is a heterodyne double-beat type, the oscillators with a remarkably high frequency stability are constrcuted. By testing several types of gas cell, it was found that one of them (cell D) can be used satisfactorily for the present purpose. For the gas filling system, a modification of Groves’ method is employed. Using this apparatus dielectric constant measurement with an error of less than 0.5 per cent can be obtained. The dipole moment of 1,1-dichloroacetone was measured in this apparatus. The moment was found to increase with temperature. This increase is attributed to the increase of the more polar isomer (b), which coexists with the form (a). The energy difference of the two isomers was found to be about 800 cal./mole. This value is smaller than that of monochloroacetone, and the lowering of ΔE was considered to be due mainly to the reduced moment of the C-Cl bonds by mutual induction. It was thereby concluded that the energy difference in these molecules is electrostatic in nature rather than steric.