Solid–solid phase transitions in azoxy compounds

Abstract

Solid–solid phase transitions in diazabicyclo-octene N-oxide, diazatricyclononene N-oxide, 1,1-dimethylazoxyethane, 1,1-dimethylazoethane and di-t-butylvinylene have been investigated by differential scanning calorimetry. The entropies of transition were 34.2, 42.4, 31.1, 20.2 and 22.9 J K–1 mol–1, respectively. Diazabicyclo-octene N-oxide and di-t-butylvinylene have two solid-state transitions. The entropies given are the sum of the two entropy increments. The two cyclic compounds have small fusion entropies, indicating that they form plastic crystals below the melting point. The entropies for the cyclic compounds are compared with those for bicyclic hydrocarbons of similar structure. The entropies of fusion for the three di-t-butyl compounds are large, with the sum of entropies of fusion and transition in the range 60–70 J K–1 mol–1.