This thesis examines the matrix isolation chemistry of some tetrazolo[1,5- ajazines. Infrared spectroscopy was the chief experimental tool employed to characterize the products formed. Computational calculations were often used to support experimental observations and assist with mechanistic arguments.
Chapter 1 looked at the isomeric 6- and 8-cyanotetrazolo[1,5-a]pyridines. When photolysed in Ar, they are converted to cyano - substituted diazacycloheptatetraenes (absorbing strongly near 1986 cm-1). Some minor by - products (2040 - 2060 cm-1)
are thought to be acyclic ketenimines formed by ring opening of the intermediate nitrenes. Following the photolysis kinetically was an excellent method to group together absorptions for each species. The diazacycloheptatetraenes were trapped in solution with amine and alcohol nucleophiles to yield new 1,3-diazepines. These are stable, mostly sublimable compounds, whose structures were identified using NMR spectroscopy.
The tetrazolo[l,5-a]pyrazine / tetrazolo[1,5-c]pyrimidine isomeric pair are explored in chapter 2. There are two photolysis products: 1-cyanoimidazole (2268 cm-1) and (2-isocyanovinyl)carbodiimide (2135 cm-1) (c.f. cyanotetrazoles in chapter 1 where 7 -
membered ring diazacycloheptatetraenes are obtained). However, from 8- chlorotetrazolo[1,5-a]pyrazine the only photolysis product is 2-chloro-1-cyanoimidazole (2269 cm-1). Mechanistic discussion based on these experimental observations and predicted energy barriers are presented.
Attention in chapter 3 turns to [1,2,3]triazolo[1,5-c]quinazoline. Photolysis in Ar is very slow. 2-(2-iminovinyl)isocyanobenzene is thought to be partly responsible for the weak product bands. Thermolysis (600 °C) gave a much clearer result. 3-Cyanoindole (2236 cm-1) is formed predominantly and identified easily by comparison to an authentic sample.
Finally, chapter 4 investigates the tetrazolo[5,1-a]isoquinoline / tetrazolo[1,5- a]quinoline system. Photolysis converts both to the same ring expanded benzannelated diazacycloheptatetraene (2020 cm-1). Ring opened 2-(2-iminovinyl)benzonitrile (2041 - 2071 cm-1) is also produced from the former. The differences in product distribution are concluded to be due to the different reactivities of the 2-quinolyl and 1- isoquinolylnitrenes.