Abstract Irradiation of 3, 4-dimethoxy-1-nitrobenzene in the presence of butylamine leads to the formation of both possible photosubstitution products, ie, 2-methoxy-4-nitro-N- butylaniline and 2-methoxy-5-nitro-N-butylaniline with the predominance of the latter. Regioselectivity of the reaction as measured by molar ratio of the two isomeric products varies with pH of the solution, ranging from 3: 1 at pH 10 to 12. The results are discussed ...