Some studies of long range shielding effects on chemical shifts

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  • Long range shielding parameters for the C-H, C=0, and thioketal groups were derived by least squares analysis of chemical shifts of C-18 and C-19 methyl groups in 5a,14a-androstane derivatives. The sensitivity of these parameters to structural approximations, concerning conformations of methyl groups and steroid framework, were studied. The C-H bond anisotropy is thought to be small, but no definitive value could be obtained. An electrostatic and a magnetic shielding mechanism were found to be operative in the cases of the carbonyl and thioketal groups. Shielding parameters for the C=0 bond agree reasonably well with previous results. The thioketal parameters are not considered physically meaningful quantitites due to the severity of approximations and the small number of equations, but they predict chemical shifts rather well. Conformational approximations, concerning methyl groups and steroid ring systems were found to have only a moderate effect on shielding parameters and calculated shifts.

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  • Copyright ¬© 1970 the author(s). Theses may be used for non-commercial research, educational, or related academic purposes only. Such uses include personal study, research, scholarship, and teaching. Theses may only be shared by linking to Carleton University Institutional Repository and no part may be used without proper attribution to the author. No part may be used for commercial purposes directly or indirectly via a for-profit platform; no adaptation or derivative works are permitted without consent from the copyright owner.
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  • 1970

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