The synthesis and study of polycyclic aromatic hydrocarbons

The work presented in this Thesis is concerned with the synthesis and spectral study of polycyclic aromatic hydrocarbons with a view to explaining the properties and constitution of these compounds. 1.2-3.4-7.8-Tribenzotetracene (I) was prepared to demonstrate the importance of benzenoid rings in the stabilisation of aromatic hydrocarbons. Examination of the series of isomeric hydrocarbons having seven rings, indicates that stability increases with the number of benzenoid rings. The synthesis of 6.7-benzopentaphene (II) was undertaken to investigate the conjugation of molecules having three branches. Spectral study of pentaphene, 6.7-benzopentaphene and trinaphthylene (III) suggests that conjugation can only take place in two branches of the molecule simultaneously. A new hypothesis for the distribution of pi-electrons in benzene is advanced, and an improved synthesis of trinaphthylene (III) is recorded. Two previously unknown linear pyrenes, 1.2-benzo-naphtho-[2".3"-7.8]-pyrene (IV) and 1.2-benzo-anthraceno-[2".3"-7.8]-pyrene (V) were synthesised and the ideas In the last paragraph were found to be fully applicable to these. The fully benzenoid hydrocarbon, 1.12-2.3-6.7-8.9-tetrabenzanthanthrene (VI) was prepared. This exhibits all the characteristics of these extremely stable compounds. Thus it is insoluble in concentrated sulphuric acid, gives an orange phosphorescence of long life in solid solution at low temperature, and is very stable thermally. The absorption spectrum was strongly shifted to the violet. The I.E. spectrum was recorded as a verification of the hydrocarbon's structure. The two hitherto unknown hydrocarbons, 1.2-3.4-5.6-tribenzocoronene (VII) and 1.12-O-phenylene-2.3-10.11-dibenzoperylene (VIII) were made. These proved to be sterically strained. In the course of these syntheses, two quino-dimethides (IX) and (X) were obtained. These are both quite stable. Various attempts to prepare 1.2-5.6-9.10-tribenzo-coronene are recorded. Nonw of these was successful, but a material which is thought to be a mixture of 7.8-benzo-naphtho-[1'.3'-1.9]-anthrene (XI) and 2.3-benzo-naphtho-[1'.3'-1.9] -anthrene (XII) was obtained. Preliminary investigations into the synthesis of 1.2-5.6-Dibenzovalene (XIII) are described and the quinone (XIV) was isolated and characterised