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ESR study of rotational motions of spin‐labeled long‐chain nitroxides in solution
Author(s) -
Sueishi Yoshimi,
Takeuchi Takashi
Publication year - 1996
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/(sici)1099-1395(199604)9:4<234::aid-poc776>3.0.co;2-#
Subject(s) - chemistry , chain (unit) , spin (aerodynamics) , rotational dynamics , computational chemistry , chemical physics , nuclear magnetic resonance , thermodynamics , organic chemistry , molecule , quantum mechanics , physics
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 (τ c ) 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 τ c . 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 τ c is discussed in terms of the difference in the strength between solute‐solvent and solvent‐solvent interactions.