Abstract High resolution NMR spectra of solutions were studied in order to find a possible explanation for the differences in transition temperatures between corresponding esters of cholesterol and thiocholesterol and within each homologous series. In this investigation, only gross changes in chemical shift of resonant lines were utilized to account for the higher thermal stability of the cholesteric mesophase exhibited by sulfur substituted derivatives. The spectra obtained for the solutions clearly demonstrate a decrease of the force constant for the carbonyl group of the thioesters and thereby support the argument that lateral forces may be mainly responsible for higher transition temperatures. However, the data are not sufficient to explain the decrease of thermal stability for the cholesteric mesophase within a homologous series.
[1]
K. Hayamizu,et al.
The relative signs of the long range spin-spin coupling constants in formic acid esters
,
1967
.
[2]
G. J. Karabatsos,et al.
Structural studies by nuclear magnetic resonance. XIII. Rotational isomerism about the alkyl-oxyoen bond of acetates.
,
1966
.
[3]
J. Sandström,et al.
Charge distributions in carbonyl and thiocarbonyl compounds
,
1964
.
[4]
N. Bhacca.
High resolution NMR spectra catalog
,
1963
.
[5]
G. Slomp,et al.
Nuclear Magnetic Resonance Studies on Some Hydrocarbon Side Chains of Steroids
,
1962
.
[6]
W. Potts,et al.
Characteristic infrared absorption frequencies of thiol esters and related compounds
,
1959
.