Polarization modulation interferometry and vibrational circular dichroism of amino alcohols

Date of Award

1991

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Advisor(s)

Laurence A. Nafie

Second Advisor

Tess Freedman

Subject Categories

Chemistry | Organic Chemistry

Abstract

This dissertation investigates two aspects of vibrational circular dichroism (VCD). First, an experimental and theoretical evaluation of polarization modulation interferometry (PMI) as an alternative to the existing double modulation method of VCD measurement is carried out. The experimental results presented in this dissertation constitute the first measurements of VCD utilizing PMI. The PMI technique requires three times the number of scans to obtain a spectral quality comparable to that of the double modulation method. The analysis of the PMI method undertaken in this dissertation attempts to explain the difficulties involved in the experimentation and the possible reasons for requiring the averaging of three data sets to obtain a high quality VCD spectrum.

Second, the source and nature of VCD intensity generation for localized hydroxyl, amine and methine stretches in (S)-2-amino-1-propanol, (S)-1-amino-2-propanol, (S)-1-dimethylamino-2-propanol, (S)-$\alpha$-phenylethanol, (S)-sec-butyl-amine and (S)-sec-butanol is investigated by means of the ring current mechanism and the local chirality concept. The local chirality concept is introduced for the first time to understand VCD intensities. The observation of strong negative VCD for some of the above molecules in the OH and NH stretching region is ascribed to presence of local environmental chirality. The ideas developed in the VCD analysis for above compounds are then utilized in conjunction with NMR measurements to investigate the conformational preferences in nonpolar and aqueous solution for a set of biologically relevant amino alcohols: (1S,2R)-ephedrine $\{$C$\sb6$H$\sb5$CH (CH(NHCH$\sb3$)-CH$\sb3$) OH$\}$, (1S,2R)-norephedrine $\{$C$\sb6$H$\sb5$CH (CH(NH$\sb2$)CH$\sb3$) OH$\}$, (1S,2R)-N-methyl-ephedrine $\{$C$\sb6$H$\sb5$CH (CH(N(CH$\sb3)\sb2$)CH$\sb3$) OH$\}$, (1S,2S)-pseudoephedrine $\{$C$\sb6$H$\sb5$CH (CH(NHCH$\sb3$)CH$\sb3$) OH$\}$, (1S,2S)-noepseudoephedrine (C$\sb6$H$\sb5$CH (CH(NH$\sb2$)CH$\sb3$) OH$\}$ and (1S,2S)-N-methylpseudoephedrine $\{$C$\sb6$H$\sb5$CH (CH(N(CH$\sb3)\sb2$)CH$\sb3$) OH$\}$. The conclusions of this investigation are not only consistent with the NMR results but also include distinction between the two gauche conformations.

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