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Computational analysis of solvent effects in $^{19}F$ magnetic resonance spectra of fluoropyridines
Dahal, Kenita
Dahal, Kenita
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2021-12
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Abstract
The effects of some solvents on the $^{19}F$ NMR shift of 2-fluoropyridine and 3fluoropyridine
were first investigated by C.S. Giam and J.L. Lyle in the 1970’s (Journal of Organic Chemistry,
1973, 95 (10), 3235-3239), and their results showed that the solvent dependence of these fluorine
chemical shifts could not be correlated with a simple function of the solvent dielectric constant.
However, they do correlate with the solvent ET(30) value, based on the solvatochromism of
Reichardt’s dye. Be that as it may, the chemical shifts of the fluoropyridines are referenced to
fluorobenzene present in the same solvent. Therefore, the influence of fluorobenzene with the
solvent is not taken into consideration, where the shifts may have been affected by the solvent
induced dependence on the chemical shifts of fluorobenzene itself.
Our goal is proper modelling of the solvent-dependence of chemical shifts, first using
implicit solvent models. We are also working towards an approach using a combination of explicit
and implicit solvent models. Our work has also focused on re-acquiring NMR data for 2- and 3-
fluoropyridine and fluorobenzene using trifluoroacetic acid as an internal standard, so that the
effects of solvent on fluorobenzene (used as the reference compound) for Giam and Lyle’s study
on the fluoropyridines can be assessed.
An acceptable modelling system is found for 2-fluoropyridine in SMD model system with
def2-TZVP/M052X basis sets for geometry optimization and B3LYP/6-31+G(D) for NMR
shielding calculations. A satisfactory correlation was seen between the calculated chemical shifts
and experimental values of 2-fluoropyridine, validating our approximations in Gaussian. However,
reliable methods are still lacking for 3-fluoropyridine.
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Thesis (M.S.)-- Wichita State University, College of Liberal Arts and Sciences, Dept. of Chemistry
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Wichita State University
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© Copyright 2021 by Kenita Dahal
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