A STUDY OF THE ELECTRONIC PROPERTIES OF SOME HETEROCYCLIC COMPOUNDS AND THE THERMAL DECOMPOSITION OF 2-METHYLAZIRIDINE / FANG JIYE

Abstract

This thesis consists of two parts. I. Study of Electronic Structure The He I and He II photoelectron spectra of isomeric thienyl-pyridines and thienyl-ethynyl-pridines were recorded. As potential monomers for the preparation of conducting polymers, the electronic and conformational structure was analyzed as well. The relationship between deduced electronic structure and formation of novel-polymer materials is discussed. The investigation results suggest that 2-(2'-Thienyl)pyridine, 2-[2-(2'- Thienyl)ethynyl)]pyridine and 3-[2-(2'-Thienyl)ethynyl)]pyridine should be considered as the "building block" candidates for the new electrically conducting polymers since they possess lower bandgaps than the rest. All the mono-and di-ethynylthiophenes were synthesized. Their electronic structure properties were discussed based on the He I and He II photoelectron spectra and other chemical analysis results, and the ? conjugated bond lengths of various isomers were compared. The spectra indicate that various orbital interactions take place between thiophene ? and ethynyl ? orbitals. The investigations indicate that, in ethynyl substituted thiophenes, interactions between ring ? and ?-substituent orbitals are stronger than those between ring ? and ?-substituent orbitals, i.e. 2,5- ethynylthiophene should be the "best" monomeric candidate for electrically conducting polymer. The relationship between deduced electronic structure and formation of novel-polymer materials is also discussed. II. Thermal Decomposition Study The thermal decomposition of 2-methylaziridine(MA) was investigated using photoelectron spectroscopic technique. The primary decomposition of MA is completed at 750 °C. N-methylvinylamine (NMVA) and N-methylethylidenimine (MEIM) were formed from MA simultaneously. The pyrolytic mechanisms were also proposed. Semiempirical calculation results indicate that MA may convert to NMVA and MEIM via two individual processes. Moreover, calculations indicate that conversion of MA to NMVA is favoured over that of MA to MEIM. At higher pyrolytic temperature (>800 °C), secondary products such as CH4, C2H4, CH3CN, HCN, NH3 and hydrocarbon were observed. The photoelectron spectrum of NMVA was recorded for the first time and the ionization bands were assigned .