Alternate Author Name(s)

Dr. Mina Houtan, PhD '78

Document Type

Dissertation

Date of Award

1977

Keywords

Organic Chemistry, Terpenes, Charge transfer

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

First Advisor

K. Keith Innes

Second Advisor

Lawrence Verbit

Third Advisor

Alfred Hassner

Abstract

The circular dichroism charge transfer (CT) spectra of the achiral acceptors TCNE, DDQ, and Vitamin K3 with chiral donors such as terpenes, steroids and β-phenylethylamine derivatives in methylene chloride at 27° were investigated. A new transition not attributable to either component alone, but due to a CT complex was observed. The donors investigated were: (-)-fenchone, (-)-menthone, (+)-camphor, (+)-endo-3-bromocamphor, 5α-cholestan-3-one, 5α-pregnan-3β-ol-20-one, testosterone, 5α-androstan-17β-ol-3-one, Δ5-androstene-3β-ol-17-one, estrone, 17-methyl-testosterone, 17-ethynyl estradiol, β-estradiol cholesterol, (-)-menthol, 3β-bromo-cholest-5-ene, (-)-α-pinene, cholesteryl-p-nitrobenzoate, cholesteryl nitrate, cholesteryl benzoate, (S)-(+)-sec-butylamine, (1S,2S)-(+)-pseudoephedrine, (S)-(-)-ephedrine, (S)-(-)-α-phenylethylamine, (S)-(+)-amphetamine, (S)-(+)-methamphetamine, (S)-(+)-2-amino-1-propanol.

A correlation has been found between measured ellipticities and the spectroscopic nature of the CT transition, i.e., π→π* and n→π* transitions in the case of TCNE complexes. The longer wavelength π→π* transitions show considerably smaller ellipticities than the shorter wavelength n→π* transitions.

The advantages of CD over UV, especially in the case of DDQ complexes, are discussed. CD has been used for the first time to study the CT spectra of DDQ complexes.

A correlation has been found between the position of the CT complex transition and the type of electron donor, i.e., complexes with hydroxyl donors (n-donors) are in the range of 310-340 nm, ketones (n-donors) 370-405 nm, double bonds or benzene rings (π-donors) 420-518 nm, amines (n-donors) 428-467 nm, when TCNE, DDQ, or Vitamin K3 are used as the acceptor.

We report for the first time the use of CD to determine the equilibrium constant and molar ellipticity of the chiral CT complexes using a variation of the Benesi-Hildebrand equation.

Using a one-meter path length cell we report for the first time a vapor phase as well as a solvent dependence CD study of (5R)-(+)-pulegone, (5R)-(-)-carvone, (+)-camphene-1-carboxaldehyde, (-)-fenchone, (-)-7,7-dimethylbicyclo [2.2.1]heptan-2-one-1-carbonitrile, (S)-(-)-α-methylbenzylamine, and (S)-(-)-α-phenylethanol. The solvents used were acetonitrile, methanol, methylene chloride, 1,4-dioxane, isooctane, and n-heptane. A linear relationship between Z-values (a solvent polarity scale) and the shift of the n→π* and π→π* transitions was found. A negative π→π* CE was found at 206 nm for (5R)-(-)-carvone whose CD spectra had previously been reported to 235 nm. (5R)-(-)-carvone with a trans configuration of the double bond with respect to the carbonyl group shows vibronic structure while (5R)-(+)-pulegone with a cis configuration shows only one maximum for both the n→π* and π→π* transitions. Two oppositely signed CE’s for (+)-camphene-1-carboxaldehyde in solution and only one negative CE for the n→π* transition in the vapor phase indicates the existence of at least two significantly populated conformers in the liquid phase. The single negative CE in the vapor phase is the resultant of the population-weighted average of all the conformers present.

(-)-Fenchone and (-)-7,7-dimethyl-bicyclo[2.2.1]-heptan-2-one-1-carbonitrile are both rigid bicyclic ketones. The latter shows vibronic structure for the n→π* transition, but (-)-fenchone shows only one broad band for the corresponding transition. (+)-Camphor was used as a model compound to investigate this difference which indicated an electronic interaction between the cyano and carbonyl group of (-)-7,7-dimethyl-bicyclo[2.2.1]heptan-2-one-1-carbonitrile.

Only very small wavelength shifts were found in the vapor and liquid phase CD spectra of the configurationally-related compounds (S)-(-)-α-phenylethylamine and (S)-(-)-α-phenylethanol, which contain the optically active benzenoid chromophore.

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