Comparison of the Acidity of Natural and Synthetic Polyenes and the Characterization of the Proposed Structures of Conjugated Protonated Products

Date of Award

2023

Degree Name

M.S. in Chemistry

Department

Department of Chemistry

Advisor/Chair

Justin Biffinger

Abstract

Linear polyenes are an important class of compounds containing two or more alternating carbon-carbon double and single bonds that are soluble in organic non-polar solvents. Determining the relative basicity of polyenes experimentally is challenging in practice because such studies require mixing non-polar polyene-organic solvent mixtures with high concentrations of moderately polar organic acids. We will present computational approaches to determining the basicity of trans-1,4-diphenyl-1,3-butadiene (DPB), all trans-1,6-diphenyl-1,3,5-hexatriene (DPH), or all trans-1,8-diphenyl-1,3,5,7-octatetraene (DPO) with trifluoroacetic acid (TFAH) in n-hexane, benzene, and chloroform solvents. Our calculations indicate that the basicities of the DPPs increase with increasing length of the polyene moiety (DPO > DPH >> DPB) in the gas phase and in both benzene and n–heptane solvents. We will also show a comparison of the computational basicities of the various secondary and tertiary protonation sites along the conjugation pathway of ��-carotene, at natural terpenoid polyene, to the synthetic polyenes. Finally, this thesis will offer preliminary chemical mechanisms for the formation of the numerous products resulting from the rearrangements of the carbocations generated as a result of protonation. These mechanisms are proposed based on the final structures of the numerous isolated byproducts from this reaction using GC-MS, IR and 1D/2D NMR spectroscopies.

Keywords

Trifluoroacetic acid Diphenylpolyenes Cyclization Dimerization Adduct

Rights Statement

Copyright © 2023, Author

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