Structure of Molecules and Internal Rotation focuses on the processes, methodologies, and reactions involved in internal rotation. The manuscript first offers information on studies on dihalogenoethanes, as well as the spectroscopic and thermal measurements of ethane and its derivatives. Discussions focus on the dielectric constant of halogenoethanes, electron diffraction, Raman effect in ethane derivatives, and entropy difference between rotational isomers. The text also ponders on internal rotation in simple molecules and paraffinic hydrocarbons. The publication examines polypeptides and related compounds and the principles and experimental methods of structure determination. Topics include Raman effect, infrared absorption, molecules with two peptide bonds, and the configuration of a polypeptide chain. The manuscript is a valuable source of data for chemists and readers interested in the structure of molecules and internal rotation.