Publication Date

1970

Document Type

Dissertation/Thesis

First Advisor

Graham, Laurine L.||Graham, John D. (Professor of chemistry)||Spangler, Charles W.

Degree Name

M.S. (Master of Science)

Legacy Department

Department of Chemistry

LCSH

Amides; Nuclear magnetic resonance

Abstract

High-resolution Nuclear Magnetic Resonance (NMR) studies of hydrogen bonding in N-monosubstituted amides at varying temperatures were carried out. Two special cases are considered, self-associated amides in (1) an inert solvent and (2) a hydrogen bonding solvent. The solutes studied are the N-monosubstituted acetamides, CH₃CONHR, where R = CH₃, CH(CH₃)₂, and C(CH₃)₃. In order to study the self-association of N-monosubstituted amides by NMR, two equilibrium constants, K₁₂ for the monomer⇌dimer equilibrium, and K̅ for n-mer+ monomer⇌(n+1)-mer equilibria, which are related to the concentration of the solution and the observed chemical shift of the solute, were used. From a series of chemical shift measurements of the hydrogen bonding proton at varying concentrations, the two equilibrium constants, K₁₂ and K̅ were obtained. Consequently the thermodynamic constants for hydrogen bonding in the self-associated amides were determined from the equilibrium constants over a range of temperatures, 20-60° C. An IBM-360/50 computer at Northern Illinois University was used for evaluating the equilibrium constants, K₁₂ and K̅, and thermodynamic constants, ΔH°, ΔS°, and ΔF°. The equilibrium constants for N-methylacetamide, N-isopropylacetamide, N-t-butylacetamide in the strongly hydrogen bonding solvent dioxane at 30° C are found to be 3.9, 3.5, and 3.0 (m.f.)⁻¹ for the monomer⇌dimer equilibrium, and 10.6, 8.0, and 4.6 (m.f.)⁻¹ for the higher species equilibria, respectively, revealing that K̅ is approximately equal to twice K₁₂. It is also found that K̅ is much larger than K₁₂ for the N-monosubstituted amide in the inert solvent carbon tetrachloride. The equilibrium constants found for N-methylacetamide, N-idopropylacetamide, and N-t-butylacetamide in the inert solvent carbon tetrachloride at 30° C are 15, 10, and 6 (m.f.)⁻¹ for the monomer⇌dimer equilibrium, and 240, 160, and 60 (m.f.)⁻¹ for the higher species equilibria, respectively. In both dioxane and carbon tetrachloride solutions of N-methylacetamide, N-isopropylacetamide, and N-t-butylacetsunide, both K₁₂ and K̅ decrease as the bulk of the N-alkyl substituent increases. The enthalpy changes on hydrogen bonding in N-monosubstituted amides were deterraineds (1) in dioxane solvent, ΔH₁₂° = -1.1 and ΔH̅° = -1.2 Kcal/mole for N-methylacetamide; ΔH₁₂° = -0.8 and ΔH̅° = -0.9 Kcal/mole for N-isopropylacetamide; ΔH₁₂° = -0.7 and ΔH̅° = -0.8 Kcal/mole for N-t-butylacetamide; and (2) in carbon tetrachloride solvent, ΔH₁₂° = -3.7 and ΔH̅° = -4.5 Kcal/moke for N-methylacetamide, ΔH₁₂° = -3.0 and ΔH̅° = -4.3 Kcal/mole for N-isopropylacetamide; ΔH₁₂° = -2.4 and ΔH̅° = -3.3 Kcal/mole for N-t-butylacetamide. The entropy and free energy changes for the hydrogen bonding in N-monosubstituted amides were also determined. In both dioxane and carbon tetrachloride solutions of N-methylacetamide, N-isopropylacetamide, and N-t-butylacetamide, -ΔH° and -ΔF° decrease as the bulk of the N-alkyl substituent increases.

Comments

Includes bibliographical references.

Extent

xii, 131 pages

Language

eng

Publisher

Northern Illinois University

Rights Statement

In Copyright

Rights Statement 2

NIU theses are protected by copyright. They may be viewed from Huskie Commons for any purpose, but reproduction or distribution in any format is prohibited without the written permission of the authors.

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