Structure electronique du thiazole et de l'isothiazole

The electronic states of thiazole studied by VUV absorption spectroscopy and ab initio configuration interaction methods

“…Differences in vibrational frequencies for the ions: IE 1 (1200, 500), IE 2 (880) and IE 4 (800 cm À1 ) [11,13] are important, but IE 3 shows no resolved fine structure [11,13]. As expected, Penning ionization electron spectroscopy (PIES) of thiazole [15,16] gives an energy envelope similar to the UV-PES for the IE 1 to IE 3 region [11][12][13][14], after allowing for the relative shift in the electron kinetic energy axes of PIES relative to UV-PES (excitation energies 19.82 and 21.22 eV, respectively). Cross-section differences observed in PIES for the combined band IE 2 + IE 3 are significantly different from the other IE, but did not assist assignment or positioning of the separate IE.…”

“…IE 2 has IE 2 A $9.95 eV, and IE 2 V 10.24 eV; only IE 3 V 10.48 eV was determined. The symmetry identification of IE 2 and IE 3 is not agreed [11][12][13][14], although Koopmans' theorem [11] led to the order: p À1 4 < p À1 3 LP À1 N . The absence of a strong 0-0band makes identification of the p À1 3 state uncertain, IE from LP À1 N are often Gaussian in shape.…”

“…The lowest ionization energy of thiazole is: adiabatic (IE A ) 9.37 and vertical (IE V ) 9.43 eV [11]. Seven vibrational members were observed on IE 1 A ; the relatively strong 0-0 band implied a p-ionisation, which was assigned to p À1 4 [11][12][13][14]. This vibrational pattern (in stick form) is used extensively in the present study, as an identifier for Rydberg states in the VUV spectrum.…”

“…A number of important thiazoles occur in nature; one forms a crucial part of vitamin B 1 (thiamine), and other examples are the fungal metabolites epothilones-A, -B and -C, important as cancer chemotherapy drugs. In order to interpret the VUV Rydberg spectrum, we also reconsider the order of cationic states previously reported in UV-photoelectron spectra (UV-PES) [11][12][13][14] and Penning ionization (PIES) [15,16].…”

Properties and Reactions of Thiazole

“…For thiazole the first experimental measurement using this technique was preformed by Salmona et al (189) who later studied various alkyl and functional derivatives in the 2-position (190,191). Substitution of an hydrogen atom by an alkyl group destabilizes the first ionization potential, the perturbation being constant for iso-propyl and heavier substituents.…”