Electron spin resonance and molecular motion of the RCH2CHCOOR' radicals in X‑irradiated ester‑urea inclusion compounds
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Date
1964-08-15
Authors
Griffith, O. H.
Journal Title
Journal ISSN
Volume Title
Publisher
Journal of Chemical Physics
Abstract
Single crystals of the inclusion compounds formed between long-chain alkyl esters and urea were x irradi
ated at room temperature, and the free radicals produced were investigated by electron spin resonance.
The 11 esters studied were diethyl adipate and the methyl, ethyl, hexyl, and octyl esters of monocarboxylic
acids. The long-lived free radicals observed in all of these compounds are of the type RCHaCHCOOR'.
These are ir-electron radicals with the unpaired electron largely localized on one carbon 2p orbital. The
coupling constants of the alcohol protons (R') were resolved in the spectra of several radicals and the
values ranged from 3 to 6 Mc/sec. The ester radicals undergo motion in the tubular cavities formed by the
urea molecules of the crystal, and this affects the magnitudes of the proton coupling constants. The de
pendence of the a-and /3-proton coupling constants on this motion is briefly considered. From the ethyl
heptanoate radical ESR data, recorded over the range of 352° to 7°±3°K, and from the room-temperature
ESR data of all eleven ester radicals, information is obtained regarding the motions and orientations of
the ester radicals. In addition, two carboxylic-acid-urea inclusion compounds were investigated, and the
orientations and motions of the well-known radicals produced in these systems (RCH2CHCOOH) are
compared to those of the ester radicals. Approximate equations are given which relate the observed a-proton
coupling constants and spectroscopic splitting factors to the diagonal elements of the a-proton tensors
and g tensors of all radicals investigated.
Description
13 pages
Keywords
Citation
Griffith, O. H. (1964) Electron spin resonance and molecular motion of the RCH2CHCOOR' radicals in X‑irradiated ester‑urea inclusion compounds, J. Chem. Phys. 4l, 1093‑1105.