Information on the rotational motion of various types of spin-labelled long-chain nitroxides was obtained from the anisotropic ESR signals. By varying the position of the nitroxide moiety along the chain, the intrinsic flexibility of molecular chain was examined. The rotational correlation times (τc) of spin-labelled long-chain nitroxides were about 10-10 s. The activation parameters for rotational motion were estimated from the temperature and pressure dependences of τc. It was found that the activation entropy observed for methyl 16-doxyl stearate is obviously large compared with those for methyl 5- and methyl 12-doxyl stearates. The results suggest an increase in the molecular motions at the end of the hydrocarbon chain. The viscosity dependence of τc is discussed in terms of the difference in the strength between solute-solvent and solvent-solvent interactions.
|Number of pages||7|
|Journal||Journal of Physical Organic Chemistry|
|Publication status||Published - Jan 1 1996|
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Organic Chemistry