NITROGEN-15 NMR AND PHOTOELECTRON SPECTROSCOPIC STUDIES OF SMALL HETEROCYCLES.
Item
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Title
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NITROGEN-15 NMR AND PHOTOELECTRON SPECTROSCOPIC STUDIES OF SMALL HETEROCYCLES.
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Identifier
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AAI8119651
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identifier
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8119651
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Creator
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CRIMALDI, KENNETH.
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Contributor
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Prof. Robert Lichter
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Date
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1981
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Language
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English
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Publisher
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City University of New York.
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Subject
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Chemistry, Organic
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Abstract
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Objectives. There were two major motivations for this work. The first was to fill the large gap existing in the ('15)N chemical shift literature for small-ring compounds. The second was to investigate the utility of ('15)N nmr as a probe of the unusual geometric and electronic properties of small rings. In the last two series (see below), PES was also used to investigate electronic properties.;The types of compounds under consideration here are as follows: (1)N-Alkylaziridines; (2)C-Alkyl and C-phenylaziridines; (3)N-Alkylazetidines; (4)N-Arylaziridines; (5)Alkyl- and arylazirines.;Results. ('15)N chemical shifts of 15 alkylaziridines, eight phenylaziridines, and six N-alkylazetidines have been measured at the natural-abundance level. The change in chemical shift with ring size up to seven atoms parallels ('13)C values of the corresponding carbocycles. The effect of N-methylation on the resonance positions decreases with ring size. N-Akylaziridines display (beta) and (gamma) effects analogous to acyclic amines; the (beta) effect decreases with branching at the (alpha) carbon. Ring alkyl groups also induce typical (beta) and (gamma) shifts, and the effect of (gamma) substitution depends on the degree of (beta) carbon branching. ('15)N shifts of 2-phenylaziridines appear to display the influence of conjugation between the two rings. The deshielding associated with that interaction is attenuated when the molecular geometry is distorted from the preferred bisected conformation. N-alkylazetidines display normal substituent effects except for N-tert-butylazetidine, which exhibits a shielding (beta) effect.;('15)N chemical shifts of ten N-arylaziridines were measured at the natural-abundance level. Good correlations were found with ('15)N and ('17)O shifts in similar systems. The range of chemical shifts is consistent with decreased interaction between the lone pair and the benzene ring relative to anilines. Dual substituent parameter analysis of the shifts revealed surprisingly high apparent resonance dependance. The steric effect of 2,6-dimethyl substitution was found to be much smaller than in dimethylanilines. Vertical ionization potentials for the three highest occupied orbitals were determined from photoelectron spectra. Attempts to correlate ionization potentials of lone-pair-like orbitals with ('15)N shifts were unsuccessful; only a general trend was observed in a plot of (pi)(,2) vs. (delta)(,N). The lack of correlation was attributed to direct interactions between the lone-pair-like orbitals and the orbitals of the substituent.;The ('15)N chemical shifts of ten azirines have been determined. These shifts are at higher shielding than those of corresponding acyclic imines. Effects of (beta) alkyl and (gamma) heteroatom substitution are comparable to those in other systems. In 2-phenylazirines, para substituents induce large ('15)N shift changes. Photoelectron spectra of nine azirines reveal a very low extent of conjugation between benzene (pi) and imine (pi) orbitals. This may be explained in terms of the triple-bond character of the azirine double bond.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
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Program
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Chemistry
