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C-NITROSO-COMPOUNDS have been known for over eighty years, the first examples being NN-dimethyl-p-nitrosoaniline,l nitrosobenzene, which was prepared by Baeyer from reaction of nitrosyl chloride with diphenylmercury, and the pseudo-nitroles obtained by Meyer 3 from the reaction of nitrous acid with secondary nitro-alkanes. These and other similar aromatic and substituted aliphatic nitroso-compounds gave blue or green solutions but also formed, in most cases, colourless crystals. Piloty, Bamberger, and others showed by molecular-weight measurements that these colour changes corresponded to the existence of two different molecular forms, i.e., a blue or green unimolecular compound and a colourless bimolecular compound. This feature distinguished C-nitroso-from N-nitroso-compounds.* A further generalisation, established by about 1905, was that primary and secondary nitroso-compounds were not capable of more than transient existence owing to rapid isomerisation to the oxime: R1R2CH*N0 ---+ R1R2C:N*OH. This generalisation, which sufficed for the compounds then known, was given a wide currency by Sidgwick and was repeated by Walker in the most up-to-date review. Exceptions to this " rule " were recognised in m-nitrosotoluene (C,H,*CH,*NO), first prepared by Behrend and Konig,, and in the substituted secondary nitroso-compounds (R*CHX*NO),, where X = C1, Br, or C0,Et. I n some cases, the name " isonitroso-compound " was given to the oxime derived from the primary or secondary nitrosocompound. I n addition, it was recognised that many of' the bimolecular tertiary nitroso-compounds dissociated into the monomer in solution or when molten and that some nitroso-compounds existed as monomers only.It was also shown that all dimeric nitroso-compounds could be dissociated to the monomer in suitable conditions, though such dissociation might only be very limited in its extent. Before 1914, German chemists (particularly Piloty, Bamberger, Wieland, Staudinger, and Schmidt) made major contributions to our understanding of these compounds; in the inter-war period

The photolyses of three N-methyl-N-nitrosoanilines and two N-methyl-N-nitroanilines in organic solvents have been studied in the range of 300-340 nm. The influence of solvent character and the presence or absence of oxygen play important roles in the product composition range. The primary photochemical process involves N-N fission, this being homolytic in aprotic solvents and heterolytic in methanol. Three novel mechanistic conclusions are proposed, namely photosolvolysis of a nitrosamine in methanol, photooxidation of nitrosamines in aprotic solvents and the production of biphenyl derivatives on photolysis of nitro-substituted nitrosamines and nitramines in aromatic solvents.The reaction of nitrogen dioxide with N-methyl-4-nitroaniline produces a variety of products. In the course of a study of these reaction products it became apparent that some of the Nnitroso and N-nitro compounds produced displayed interesting photochemical reactions. Our earlier studies on the photochemistry of many C-nitroso compounds 1 and a couple of Nnitroso compounds 2 had demonstrated the importance of solvent character in photolyses where nitric oxide was a primary photochemical product. It was therefore of interest to study the photolyses of aromatic N-nitroso compounds paying attention to any differences between protic and aprotic solvents. The compounds chosen in this investigation comprise three nitrosamines and two nitramines.

IT is well known that the temperature-dependence of the velocity constant (k) of a reaction can be written in the formwhere E is the energy of activation and A is termed the Arrhenius factor. ( A is alternatively termed the frequency factor, temperature-independent factor, non-exponential factor, and pre-exponential factor.) It is obviously desirable to be able to calculate Arrhenius factors from first principles and thereby to understand the precise nature of their dependence, if any, on temperature or pressure.When the transition-state theory is applied to unimolecular reactions two possible cases can emerge.l By this theory