The molecular structure and the rotational isomerism ofn‐propyl chloride were investigated by means of the sector‐microphotometer method of electron diffraction. The following structural parameters were obtained: C&sngbnd;Cl=1.775±0.02 A, C&sngbnd;C=1.535±0.02 A, and ∠C&sngbnd;C&sngbnd;Cl=111°±2°. It was confirmed that there are two isomers in the vapor phase; one is thetrans‐form, and the other is thegauche‐form. From the analysis of the scattering intensity of the small‐angle region (q=5∼15), the angle of ∠C&sngbnd;C&sngbnd;C, the azimuthal angle of thegauche‐form, and the fraction of thetrans‐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 thegauche‐form is only a few hundred calories/mole more stable than thetrans‐form, in fairly good agreement with the spectroscopic results. The procedure used in the analysis of the small‐angle region is described in detail.
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