Document Type

Dissertation

Date of Award

1974

Keywords

Liquid crystals, Circular dichroism

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

First Advisor

C. Max. Hull

Second Advisor

John J. Eisch

Third Advisor

Howard Alper

Series

Science and Mathematics

Abstract

Part One of this work is a correlation of molecular structure with mesophase formation and stability. Since it has been established that mesogenic compounds are linear, rigid, and contain polarizable electron density, the synthetic approach restricts molecular structure to include these properties. In order to correlate mesomorphism with molecular structure, the central groups and terminal substituents were systematically altered, and electronic and steric factors are discussed in relation to mesophase formation and stability. Some p-substituted phenyl esters of acetylenedicarboxylic, fumaric, maleic, mesaconic, cyclohexanedicarboxylic, and benzoic acid were prepared. It was found that deviation from linearity decreased mesophase stability. On the other hand, increased polarizability along the molecular axis enhanced mesophase stability.

Part Two, a study of the circular dichroism of α,β-unsaturated diesters, includes synthesis and spectra of the optically active menthyl and bornyl esters of acetylenedicarboxylic, maleic, and fumaric acids. The ultraviolet spectrum of each ester exhibits a maximum at 195-210 nm assigned to a π→π* transition and a shoulder at ~ca. 270 nm due to an n→>π* transition. Each ester exhibited a strong negative Cotton effect in the region of the π→π* transition.

In the region of the n→π* transition in the ultraviolet spectrum, the maleate esters displayed one Cotton effect but the fumarate and acetylenedicarboxylate esters exhibited two overlapping Cotton effects. In order to determine the origin of the observed Cotton effects, solvent dependent and variable temperature CD studies were performed. The data are best interpreted in terms of a restriction to one conformation in the maleate esters, and in terms of a conformational equilibrium between cisoid and transoid rotamers in the cases of dibornyl acetylenedicarboxylate and in dibornyl and dimenthyl fumarate.

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