I. GAS PHASE NITROSATION OF BENZENE: IMPLICATIONS FOR SOLUTION ELECTROPHILIC AROMATIC SUBSTITUTION REACTIONS. II. GAS PHASE BINDING ENERGIES AND SPECTROSCOPIC PROPERTIES OF NITROSYL ION CHARGE-TRANSFER COMPLEXES. III. GAS PHASE NITROSYL ION COMPLEXES WITH AROMATICS: IMPLICATIONS FOR ELECTROPHILIC AROMATIC SUBSTITUTION REACTIONS. IV. PHOTODISSOCIATION OF PROTONATED BETA-DIKETONES IN THE GAS PHASE

WILLIAM DAVID REENTS, Purdue University

Abstract

In this work the structures and properties of gas phase NO('+) complexes are studied with emphasis on their relevance to electrophilic aromatic substitution reactions. Also, the photodissociation of protonated (beta)-diketones are examined and mechanisms are proposed for the dissociation process. In Part I the structures of nitrosated benzene, C(,6)H(,6)NO('+), and protonated nitrosobenzene, C(,6)H(,5)NOH('+), in the gas phase were examined and compared to similar species in solution. The solution phase intermediate in the nitrosation reaction, a (sigma)-complex, was found to exist as a high energy specie in the gas phase which prevented the gas phase substitution reaction from occurring. The results suggest a charge-transfer mechanism for nitrosation and nitration in solution. In Part II the NO('+) affinities (NOA) of 28 bases were determined using ion cyclotron resonance (ICR) spectrometry. The NOAs are observed to correlate with the proton affinities (PA) and the first ionization potentials (IP) of the bases for a specific class of compounds. The linearity with IP suggests that bonding to NO('+) is through the highest filled orbital. Exceptions to the correlation with IP (C(,6)H(,5)CF(,3), C(,6)H(,5)F and C(,6)H(,5)Cl with the alkylbenzenes) are found to correlate better with their second IP suggesting that in these cases the second highest filled orbital is involved with bonding to NO('+). The photodissociation spectra of the NO('+) complexes were obtained as well. The spectra were identical within a class of compounds but differed between classes. Also, the spectra changed when the charge location (base vs. NO) changed. In Part III the experimental and theoretical properties of aromatic NO('+) (pi) complexes are examined to gain insight into gas phase and solution electrophilic aromatic substitution reactions. In Part IV the gas phase photodissociation spectra of four protonated (beta)-diketones were obtained and compared to the absorption spectra of the corresponding ions in solution. Photodissociation of the protonated alkyl (beta)-diketones is believed to occur from the protonated keto form whereas photodissociation of protonated, 1,1,1-trifluoro-2,4-pentanedione is believed to occur from the protonated enol form. Mechanisms for the observed photodissociation processes are proposed and comparisons with results from related techniques are presented.

Degree

Ph.D.

Subject Area

Analytical chemistry

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