On the origin of the high density of liquid cyclohexane

Cyclohexane and 2,3-dimethylbutane molecules are the most compact among saturated C6-hydrocarbons. They have a similar size and are arranged in the liquid phase like atoms in simple liquids. However, the cyclohexane density is higher approximately by 20% than that of 2,3-dimethylbutane. The reasons of this distinction are discussed. It can be explained within the concepts of the physics of simple liquids. According to them, a small variation of the radius of a particle hard core or the pair interaction energy can lead to appreciable changes in the structure and density of a liquid. The obtained results give grounds to discard the explanations based exclusively on the features of the shape of the given molecules.