Investigation of Rotational Isomers with Ultrasound

Sound absorption measurements in organic liquids have revealed relaxation processes in some cyclohexane derivatives, cyclohexene, methyl formate, ethyl acetoacetate, acetic anhydride, and methyl benzoate. Additional absorption measurements have been made in the relaxation regions of formic acid, ethyl formate, methyl acetate, and ethyl acetate. A study of cyclohexane derivatives and other similar ring molecules has led to the identification of the mechanism responsible for the relaxations in these liquids. The relaxation phenomena are attributed to the disturbance by the sound wave of equilibria between rotational isomers. The restricted rotation occurs about the single bonds in the ring during the conversion from one chair configuration to another. The relaxation in cyclohexene is caused by the disturbance of the equilibrium between pseudochair and boat configurations, again involving rotation about single C–C bonds. The relaxations in esters of the carboxylic acids are attributed to rotational isomers which arise from rotation about C–O bonds. Infrared absorption bands at about 1160 and 1185 cm-1 in the formates and acetates are identified with rotational isomers of the type postulated for the relaxations in these liquids.

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