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.

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The vapour phase absorption spectrum of nitrosomethane in the 600-72Onm region has been re-examined. The overall complexity of the spectrum is shown to be due to a conformational change from the eclipsed ground state to a staggered excited state. The prominent torsional features have been reassigned and are found to be consistent with a barrier of 500+ 100 cm-' to internal rotation in the excited state. Progressions of 390 and 1420 cm-1 have been assigned to the CNO bending and NO stretching modes in the excited state. Only one electronic absorption system with a Franck-Condon forbidden origin at 694.1 nm corresponding to the 'A" +-'A' (L, T*) transition has been observed .The geometry changes accompanying electronic excitation have been estimated using ab initio calculations for the 'A" state. A substantial lengthening of the CN and NO bonds, a widening of their bond angle and a change in the phase of the torsional barrier are predicted.* h = 1 hartree = 2.1948 x lo5 cm-l.

The rates of nitrosodealkylation of severat symmetrical tertiary amines R,N including trialkylamines (R = Me, Et, Pr", and Bun) and substituted trialkylamines (R = C6H5CH2, triethanolamine, and nitrilotriacetic acid) have been measured in aqueous acetic acid-acetate buffers. The rate of formation of diethylnitrosamine was found to be first order in nitrous acid, triethylamine, and in the hydrogen ion concentration for pH >3.1. Rates increased with decreasing amine basicity. The rate equation was consistent with rapid, reversible nitrosation by nitrous acid or acetyl nitrite and a rate-determining subsequent elimination.

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