Disertation (Ph.D.)--Worcester Polytechnic Institute. / Keywords: cyanopyridine; methylpyridine; pyridine; phototransposition; azaprefulvene Includes bibliographical references (317-321 ).

The vapor phase photochemistry of the three isomeric cyanopyridines and the three methylpyridines was studied by irradiating their vapors at 254 nm. It was found that direct irradiation of any one cyanopyridine isomer resulted in the formation of the other two isomers of cyanopyridine or methylpyridines respectively. The reactivity of each isomer was found to be different. This was suggested to be based on the stability of their azaprefulvene intermediates formed during interconversion. The phototransposition of these molecules was suggested to result from 2,6-bonding, nitrogen migration around the five sides of cyclopentenyl ring followed by rearomatization. This mechanism was found to be consistent with the results of deuterium labeling studies of cyanopyridines These result suggest that cyanopyridines undergo phototransposition via the intermediacy of azaprefulvenes instead of Dewar-pyridine and azaprismane. Thus, photochemical studies showed that the six trideuteriopyridine isomers constitute two separate photochemical triads. Each triad consists of three isomers that are photointerconverting upon irradiation at 254 nm in the vapor phase. Similary, it was found that the three isomeric tetradeuteriopyridine isomers also constitute a photochemical triad and are interconverting upon irradiation at 254 nm in the vapor phase. These phototranspositions are best explained by the cyclization, nitrogen migration, and rearomatization mechanism. These results are in contrast to the long-held belief that pyridine is photostable in the vapor phase. Instead, unlabeled pyridine undergoes a hidden phototransposition leading back to itself.

Orientador: Pedro Oliver Dunstan Lozano / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-22T07:28:40Z (GMT). No. of bitstreams: 1 Khan_AbdulMajeed_D.pdf: 3004508 bytes, checksum: 1d8c778094bf0cb1b93fa7bf80e19074 (MD5) Previous issue date: 2013 / Resumo: Os adutos MX2.nL (M = Mn, Fe, Co, Ni, Cu ou Zn, L = 3-cianopiridina, piperidina ou piperazaina, X = Br, n = 0,5, 0,75, 1, 1,5, 2 ou 4), foram sintetizados e caracterizados através de análise elementar, determinação de pontos de fusão, espectroscopia IV e eletrônica e análise termogravimétrica. Todos os adutos são sólidos e sensíveis à umidade atmosférica. Os dados espectroscópicos na região do infravermelho, para os adutos, indicam a presença de um mesmo padrão de bandas em comparação com os respectivos ligantes livres. No entanto, deslocamentos de algumas bandas são evidentes devido à coordenação dos íons metálicos aos ligantes. As entalpias de dissolução em HCl 1,2 molL dos adutos, brometos metálicos e ligantes, foram determinados. Através de ciclos termoquímicos apropriados, foram calculadas as variações de entalpia padrão para as reações: MBr2 (s) + nL (s,l) MBr2.nL (s) DrH MBr2.nL (s) MBr2 (s) + nL (g) DDH MBr2 (g) + nL (g) MBr2.nL (s) DMH Foram também calculadas as variações entálpicas padrão de formação dos adutos e as variações entálpicas padrão da ligação metal-nitrogênio. Os parâmetros termoquímicos permitiram determinar a ordem de acidez dos adutos: para os adutos de ligante 3-cianopiridina: NiBr2>FeBr2> CoBr2>MnBr2 e ZnBr2>CuBr2, para os adutos de ligante piperidina: FeBr2 > MnBr2, CoBr2 > NiBr2, para adutos de ligante piperazina: FeBr2 > MnBr2 > NiBr2 e CuBr2 > ZnBr2 > CoBr2. A ordem de basicidade das ligantes e (Piperidina) >(3-cianopiridina) para os adutos de ZnBr2 e (Piperidina) > (Piperazina) para os adutos de CuBr2. / Abstract: The adducts MX2.nL (M = Mn, Fe, Co, Ni, Cu or Zn, L = 3-cyanopyridine, piperidine or piperazaina, X = Br, n = 0.5, 0.75, 1, 1.5, 2 or 4), were synthesized and characterized by elemental analysis, melting point measurements of the adducts, vibrational and electronic spectroscopy and thermogravimetric analysis. All adducts are solid and sensitive to moisture. The spectroscopic data in the infrared region, indicate the presence of a similar band pattern as compared with the free ligands. However, dislocation of some bands are observed due to coordination of the metal ions to the ligands. The enthalpies of dissolution in HCl 1.2 molL of the adducts, metal bromides and ligands have been determined. Through appropriate thermochemical cycles, we calculated the standard enthalpy changes for the reactions: MBr2 (s) + nL (s,l) MBr2.nL (s) DrH MBr2.nL (s) MBr2 (s) + nL (g) DDH MBr2 (g) + nL (g) MBr2.nL (s) DMH Standard enthalpy of formation and standard mean enthalpy of Metal-Nitrogen bonds were also calculated. The thermochemical parameters allowed to determine the acidity order of metal bromides for the adducts of the same stoichiometry: For the adducts of ligand 3-cyanopyridine: NiBr2> FeBr2> CoBr2> MnBr2 and ZnBr2> CuBr2. for the adducts of ligand piperidine: FeBr2> MnBr2 and CoBr2> NiBr2. for the adducts of ligand piperazine: FeBr2> MnBr2> NiBr2 and CuBr2> ZnBr2> CoBr2. The order of basicity is (Piperidine)> (3-cyanopyridine) for the adducts of ZnBr2 and (Piperidine)> (Piperazine) for the adducts of CuBr2. / Doutorado / Quimica Inorganica / Doutor em Ciências