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'Objective' determination of coupling constants and conformational equilibria by solvent variation: a re-evaluation

Deutsch, Phillip T. and Roberts, John D. (2005) 'Objective' determination of coupling constants and conformational equilibria by solvent variation: a re-evaluation. Magnetic Resonance in Chemistry, 43 (5). pp. 417-423. ISSN 0749-1581. doi:10.1002/mrc.1566.

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An ‘objective’ method for determining conformational equilibria in substituted ethanes, proposed by Abraham et al., has been evaluated by computational methods. Abraham's method involves measuring vicinal couplings, such as ^3J(H,H) and ^3J(H,F), between methine and methylene protons with methine, methylene protons and fluorine in a range of solvents, on the assumption that the underlying coupling constants of the individual conformers are constant, but the fractions of each conformer in each solvent are different and unknown. Abraham posited that this would produce an ‘over-determined’ data set with more equations than unknowns would. Abraham's procedure is re-evaluated, and it is demonstrated that the type of system being considered here, where there are more equations than unknowns, is not necessarily over-determined. A computer equation solver and Monte Carlo-type procedures were employed to demonstrate that multiple numerical solutions exist for a representative ‘over-determined’ data set provided by Abraham. A statistical method was also developed to determine precisely which parameter sets constitute plausible solutions.

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Additional Information:© 2005 John Wiley & Sons, Ltd. Received 1 November 2004; Accepted 11 January 2005. Article first published online: 4 Mar 2005. Acknowledgment is made to the donors of the Petroleum Research Fund administered by the American Chemical Society for support of this research. We are also deeply indebted to the support by the National Science Foundation under Grant No. CHE-0104273, the Summer Undergraduate Research Fellowship Program (SURF) at the California Institute of Technology, the Camille and Henry Dreyfus Foundation, Merck and Company, the E. I. DuPont Company and Dr and Mrs Chester M. McCloskey for their helpful financial assistance.
Funding AgencyGrant Number
American Chemical Society Petroleum Research FundUNSPECIFIED
Caltech Summer Undergraduate Research Fellowship (SURF)UNSPECIFIED
Camille and Henry Dreyfus FoundationUNSPECIFIED
Merck and CompanyUNSPECIFIED
Dr. and Mrs. Chester M. McCloskeyUNSPECIFIED
Subject Keywords:NMR; 1H NMR; conformation; conformational equilibrium; solvent variation; substituted ethanes; computational methods; conformer ratio
Issue or Number:5
Record Number:CaltechAUTHORS:20150930-125952939
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Official Citation:Deutsch, P. T. and Roberts, J. D. (2005), ‘Objective’ determination of coupling constants and conformational equilibria by solvent variation: a re-evaluation. Magn. Reson. Chem., 43: 417–423. doi: 10.1002/mrc.1566
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:60616
Deposited By: Ruth Sustaita
Deposited On:01 Oct 2015 17:39
Last Modified:10 Nov 2021 22:36

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