(1) The pyrolysis of benzoic 5-benzyl-2-furoic anhydride by using SS-FVP method can obtain the ring-opened product naphthalene, and no ring-contracted product and its further derivatives. (2) Flash vacuum pyrolysis (FVP) of 2-(2-azidoethyl)thiophene, via a nitrene intermediate gave 1,2-di(2-thienyl)ethane, 3,5-di(2-thienyl)pyridine, and 2-methylthiophene as the main products.

(1) Flash vacuum pyrolysis (FVP) of (5-methyl-2-selenophenyl)methyl benzoate gave 4-methylene-4H-selenopyran. The structure was confirmed by trapping experiment. The mechanism for the 4-methylene-4H-selenopyran will be discussed. (2) Flash vacuum pyrolysis of 2-Azidomethylselenophene, via a nitrene intermediate, gave a trimer (N,N¡¦-di-2-selenophenylmethylidene-2-selenophenylmethylidene diamine).

Flash vacuum pyrolysis (FVP) of 2-azidoacetophenone gave the dimer 2-benzoyl-4- phenylimidazole and the trimer: 2,3-dibenzoyl-5-phenylpyrazine. Flash vacuum pyrolysis of 2-azido-1-(2-thienyl)ethanone gave the dimer: 2-(2-fromylthienyl)-4-(2-thienyl)imidazole and 2-formylthiophene.

Flash vacuum pyrolysis (FVP) of 2-azido-1-(1-methyl-2-pyrryl)ethanone and 2-azido-1- (2-benzo[b]thienyl)ethanone gave nitrene by elimination of one nitrogen molecule. When 2-azido-1-(1-methyl-2-pyrryl)ethanone as a precorsor, the reactive nitrene readily underwent self-condensation to give 2-(1-methyl-2-formylpyrryl)-4-(1-methyl-2- pyrryl)imidazole, it¡¦s isomer and 2,4,5-tri(1-methyl-2-formylpyrryl) imidazole. While 2-azido-1-(2-benzo[b]thienyl)ethanone as a precorsor, the reactive nitrene readily underwent self-condensation to give 2-2-formylbenzo[b]thienyl-5-(2-benzo[b]thiophen-2-yl)imidazole. The mechanism for the formation of products of self-condensation reaction from FVP of 2-azido-1-(1-methyl-2-pyrryl)ethanone and 2-azido-1-(2-benzo[b]thienyl) ethanone will be discussed.

Abstract¡G ¤@¡B trans o-Thiomethoxystilbene and its derivatives 19a-c had been studied by means of pyrolysis and photolysis. Under pyrolytic conditions, compounds 19a-c gave not only the products 24¡B30¡B33,but also their corresponding isomers 26¡B31¡B34 . Furthermore, compound 19c gave dibenzothiophene (32) as the major product by opening the furan ring at higher temperature. Under photolytic conditions, compounds 19a-c gave the corresponding photocyclic products 40¡B44¡B46. With the exception of 19c, photolysis of 19a and 19b also gave 24 and 30, respectively. ¤G¡B For synthetic study of thieno-fused derivatives 4 and 5 of truxene, preparation monomer 6 and 7 can be accomplished in two steps by means of flash vacuum pyrolysis.

A vacuum interrupter is a switching device used in vacuum circuit breakers, which are widely employed in medium voltage circuits for interrupting the short-circuit fault currents. The vacuum interrupter is the chamber in which the arc extinction and hence the current interruption takes place. On the occurrence of a fault, the breaker mechanism separates the contacts of the vacuum interrupter. As the contacts separate, an arc is established between the contacts. The arc evolves in the contact space and extinguishes at or near the current zero, thus interrupting the current. The processes of arc ignition, evolution and extinction are very complex. These processes are fundamental to the design and the performance of the vacuum interrupter and hence the circuit breaker. The evolution of the arc predominantly depends on the short-circuit current, the design and metallurgy of the contacts. The evolution of the vacuum arc has been the focal point of considerable research activity. Significant effort has been concentrated to understand the various modes of the arc, the transition between the modes, the arc movement and the dependency on the contact design and finally the effect of the arc evolution on the current interruption performance of the vacuum interrupter. The voltage across the contacts during the arcing, termed as the arc voltage, has been a focal point of several research projects. Research has shown that the arc voltage depends strongly on the mode and the evolution process of the arc. The dependency is observed with respect to the magnitude and the nature of the arc voltage. This dependency has been established through the comparison of the arc voltage trace and the actual arc photographs. The arc voltage is thus an important parameter in understanding the arcing process in the interrupter. Arc voltage could also be utilised to compare the arcing behaviour in vacuum interrupters with different contact geometries and metallurgies. Having understood how the arc voltage depends on the arc modes and how it can be used to analyse the arcing performance of the interrupter, this work aims to establish experimentally the dependency of the arc voltage on fundamental parameters of the short-circuit current and the contact design. The variation of the arc voltage is studied with respect to the magnitude of the short-circuit current. It is seen that the magnitude of the arc voltage is higher, for a higher short-circuit current. This dependency is also reflected in the nature of the arc voltage waveform. The effect of cumulative short- circuit operations has been understood through the study of arc voltage variation with respect to the accumulated arcing time. It has been found that the arc voltage consistently decreases as the accumulated arcing time increases. The effect of the contact diameter on the arc evolution has been studied by comparing the arc voltage variations for contacts of different diameters for the same short-circuit current. It is observed that the variation of arc voltage with respect to the contact diameter depends on the type of contact. In the case of radial magnetic field contacts, it has been observed that the arc voltage is lower for a contact with lower diameter. Whereas in the case of axial magnetic field contacts there is an inverse relation between the contact diameter and the arc voltage. Finally, the effect of the type and distribution of the magnetic field on the arc voltage variation as well as the contact erosion has been studied. In general, the observations show that the arc voltage magnitude for the radial magnetic field geometry is higher than the axial magnetic field geometry. Also, there is a significant difference in the appearance of the arc voltage waveforms for the arcs under the two types of magnetic fields. Finite element simulations and short-circuit evaluations have shown that the axial magnetic field contact system with 90 deg coil orientations yield a more uniform distribution of the flux density and hence lower erosion of the contacts. These results show a clear dependence of the arc voltage on the various above mentioned parameters. Thus the arc voltage could be utilised as a diagnostic parameter during the evaluation of the vacuum interrupter. In the present scenario, significant research is being done to increase the breaking capacity of the interrupters. This calls for optimization of design of the existing contacts and the design of novel contact geometries. The arc voltage would be used as an important diagnostic tool in this process. Also, the utilization of vacuum interrupter in high voltage and extra high voltage circuits is being explored. This application requires increase in the contact gap or series connection of gaps. The arc behaviour in longer gaps and gaps connected in series would be an important research area. Again the arc voltage could be used to study the arc evolution in these specialised conditions. The experiments in this research work have been performed on commercial vacuum interrupters. For a dedicated research on vacuum arcs and vacuum interrupter contacts, development of a vacuum arc research facility has also been attempted as a part of this research work.

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