Understanding Long-Chain Melting Points,Fritz Breusch,and Interface Thermodynamics

A homologously isomorphous series of compounds can allow determination of local contributions to crystal properties. Historically, melting points have contributed little to structural theory, but those of a series of long-chain diacyl peroxides allow the measurement of localized structural contributions to solid-state thermodynamics, and demonstrate that a bromine substituent at a lamellar interface can make negative contributions to both the enthalpy and entropy of fusion, thus acting more “liquid-like” when in the crystal than when in the melt. We discuss how Istanbul, and opposition to Hitler, led Friedrich Breusch and his students to measure at least 1242 accurate melting points, and how this legacy may prove valuable in understanding crystalline solids, especially those that show odd-even melting-point alternation.