NMR studies of isotope effect, geometric configuration, and hydrogen bonding

Xinjie Wu, Purdue University

Abstract

In this thesis, the following data have been documented based on the author's NMR study: the deuterium isotope shift in water is $-$0.032 ppm in benzene and $-$0.024 ppm in DMSO-d$\sb6$; the oxygen-18 isotope shift in water is $-$0.0032 ppm in benzene; the H-D coupling constant in HDO is 1.08 Hz, and the corresponding H-H coupling constant in H$\sb2$O is 7.04 Hz; the deuterium isotope shift in ammonium ion is +0.029 ppm; the nitrogen-15 isotope shift in the ammonium ion is $-$0.0015 ppm; the carbon-13 isotope shift in methanol is $-$0.0022 ppm; the boron-11 isotope shift in tetrahydroborate ion is $-$0.0030 ppm. Deuterium isotope effects on one-bond and three-bond spin-spin coupling also have been studied. Some new applications of isotope effect in structure determination such as the distinguishing of amino and imino proton from hydroxyl or carboxyl proton have been illustrated with practical examples. Specific assignments have been made for the two prochiral geminal protons on the positively charged nitrogen atom of proline by one and two dimensional NOE experiments. Proton that resonates up-field is cis to the alpha-carbon proton; that that is farther down-field is trans to the alpha-carbon proton. A procedure for determining strength of hydrogen bonding by NMR has been established, and the following data have been determined: the strengths of hydrogen bonding between water and dichloromethane, between water and dimethyl sulfoxide, between water and water, and between methanol and methanol are 1.503 $\pm$ 0.025 kcal/mol, 5.908 $\pm$ 0.434 kcal/mol, 2.244 $\pm$ 0.141 kcal/mol, and 2.249 $\pm$ 0.042 kcal/mol, respectively. No significant difference in hydrogen bonding ability between H$\sb2$O and HDO was found in this research.

Degree

Ph.D.

Advisors

Markley, Purdue University.

Subject Area

Analytical chemistry

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