Perhydropyren, ein beim Phasenübergang hüpfender Kohlenwasserstoff

Abstract

Polarizing microscopy and differential scanning calorimetry measurements on crystals of three (1a-c) of the 14 diastereoisomers of perhydropyrene (hexadecahydropyrene) led in the case of 1a^[1] to the discovery of a reversible solid-solid phase transition (ΔH ≈ ±1.4 kJ/mol) originating an unusual, interesting combined mechanical and optical behaviour. On heating above ca. 71.5°C as well as on subsequent cooling below ca. 65.5 °C crystals of 1a show abrupt vigorous movements and a change of interference colours, each time these two temperatures are passed; especially in the cooling process loose, uncovered crystals may hop about 6 cm high! This «colour and hopping effect» of 1a can be observed many times on taking the same sample through this heating and cooling cycle. – In comparison to 1a a derivative of hexahydroxycyclohexane (myo-inositol) is discussed briefly which displays this «colour and hopping effect» even at two temperatures.