Electron Diffraction Study on the Rotational Isomerism in n-Propyl Chloride

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Abstract
The molecular structure and the rotational isomerism of n-propyl chloride were investigated by means of the sector-microphotometer method of electron diffraction. The following structural parameters were obtained: C–Cl=1.775±0.02 A, C–C=1.535±0.02 A, and ∠C–C–Cl=111°±2°. It was confirmed that there are two isomers in the vapor phase; one is the trans-form, and the other is the gauche-form. From the analysis of the scattering intensity of the small-angle region (q=5∼15), the angle of ∠C–C–C, the azimuthal angle of the gauche-form, and the fraction of the trans-form were found to be 109.5°±2.5°, 59°±5°, and 19±5%, respectively. It was also found through the calculation of the partition functions that the gauche-form is only a few hundred calories/mole more stable than the trans-form, in fairly good agreement with the spectroscopic results. The procedure used in the analysis of the small-angle region is described in detail.