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Published October 2002 | public
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Effect of pH on the rotational conformations of 1,3-diamino-2-hydroxypropane

Cheng, Jim M.
Heller, Jessica P.
Petterson, Krag A.
Roberts, John D.
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Abstract

The effect of pH on the rotational conformations of 1,3-diamino-2-hydroxypropane in aqueous solution was investigated by proton NMR. Both the observed chemical shifts and coupling constants were used to calculate experimental pK_a values. The observed couplings were correlated with the expected couplings for the various possible staggered conformations to try to determine the pattern of conformations for the diamine and its conjugate acids. The best fits suggested a modest preference for the gauche–gauche conformation, especially at low pH, where the diprotonated hydroxydiamine predominates. In methanol, dimethyl sulfoxide and trichloromethane solutions, it was only possible to evaluate the conformational equilibria of the diamine. Slow proton exchange, which caused uncertainties in both chemical shifts and couplings for the monoprotonated and unprotonated diamine, nullified efforts to determine whether or not hydrogen bonding was important for these species in less polar solvents.

Additional Information

© 2002 John Wiley & Sons, Ltd. Received 21 January 2002; Revised 7 June 2002; Accepted 4 July 2002. Article first published online: 15 Aug 2002. 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 Summer Undergraduate Research Fellowship Program (SURF) for major assistance, and to the E. I. Du Pont Company, Dr and Mrs Chester M. McCloskey and the Camille and Henry Dreyfus Foundation for their financial assistance. We also thank Francoise Gregoire for her assistance in the course of this research.

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Created:
August 21, 2023
Modified:
October 24, 2023