The structure characterization of molecules with ESR spin labels of pyroline and piperidine type

Abstract

Alkanes and most of their -and , -substituted derivatives show a remarkable alternation in their melting points with increasing chain length [1,2]. The same phenomenon also occurs within series of substances with a constant number of C-atoms. One of these isomeric series are the octenes where the melting points of the 2-and 4-octenes are relatively higher than those of 1-and 3-octenes. This holds for the series of cis-as well as for the series of trans-isomers.Single crystals of all trans-octenes have been grown in situ using a miniature zone melting procedure [3], and their X-ray analyses have been carried out. Crystal structures of cis-octenes have been determined by X-ray powder diffraction using lattice energies minimisations [4]. The structural similarities and differences between the trans-and cis-isomers of each serie could be analyzed based on the packing arrangements of hydrocarbon chains and the end groups. The melting point alternation in both isomeric series can be explained based on the calculations of lattice energies.