Flash vacuum pyrolysis(FVP) of azidomethylthiophene,via a nitrene intermediate,gave two products,a dimer (thienylmethylidene-thienylamine) and a trimer (N,N`-dithienyl methylidene-thienylmethylidene diamine).The trimer underwent cyclization and dehydrogenation to afford 2,4,5-trithienylimidazole. However by the same route, FVP of azidomethylbenzo[b]furan produced only a trimer(dibenzo[b]furylmethylidene-N,N'-benzo[b]furylmethyl amine).

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.

Flash vacuum pyrolysis (FVP) of azidomethylthiophene, via a nitrene intermediate, gave a trimer (N,N`-trifurfurylidene-furfurylidene diamine). Use three kinds of methods to synthies benzofuran compound and gain the product by using the third method.

¤@¡BPyrolysis of 2-azido-1-(4-methoxyphenyl)ethanone (69) and 2-(2-azidoethyl)furan (85) gave nitrene intermediate to study. There is 2-(4-methoxybenzoyl)-4-(4- methoxyphenyl)imidazole (81) ¡B2-(4-methoxybenzoyl)-5-(4-methoxyphenyl) imidazole] (81¡¦)¡B2,3-di(4-methoxybenzoyl)-5-(4-methoxyphenyl) pyrazine] (82) and 3,5-di(2-furyl) pyridine (92) for pyrolysis products. ¤G¡BPyrolysis of3-methyl-2-cyclohexen[b] furylmethyl benzoate) (50) gave carbene intermediate to study. There is 2,3-dimethylene cyclohexen[b]furan (59) for pyrolysis products.

Gas-phase electron diffraction (GED) is the only viable technique for the accurate structural study of gas-phase molecules that contain more than ~10 atoms. Recent advances in Edinburgh have made it possible to study larger, more complex, stable molecules using the SARACEN method. This thesis is concerned with obtaining the structures of unstable species, using both standard GED techniques and by developing a new method in which ash vacuum pyrolysis is used to generate short-lived species in situ. In the first part of this thesis nine primary phosphines (R-PH2) with different substituents (R = methyl, vinyl, ethynyl, allenyl, allyl, propargyl, phenyl, benzyl and chloromethyl) are studied by GED. Vinylarsine and vinyldichloroarsine are also studied. Primary phosphines and arsines appear infrequently in the literature owing to their toxicity and high reactivity, especially of the unsaturated systems. The conformational behaviour in these molecules and trends throughout the series are rationalised. As appropriate, comparisons are made to analogous amines and the differences found are discussed. Tertiary phosphines (R3P) are routinely protected by complexation with borane (BH3) and it has been proposed that this technique could be extended to primary phosphines. As an extension of the initial investigation, the GED study of methylphosphine-borane offers an insight into structural changes that occur upon complexation, although attempts to study larger phosphine-borane complexes by GED proved dificult. The structures and bonding trends in a series of phosphineborane adducts are discussed, mainly using the results of ab initio calculations. The second part of the thesis details the implementation of a new, very high temperature nozzle, which allows the generation of short-lived species by pyrolysis. The workings of this nozzle are discussed and the study of the structure of ketene, generated from three different precursors, is detailed. The benzyl radical has also been studied, and a preliminary GED structure is presented. As a result of this work the molecular structures of Meldrum's acid and dibenzylsulfone are also presented, having been determined in the gas phase for the first time.