The photocatalysed reaction of five selected organic systems, namely 2,2'-dinitro biphenyl (1), N,N'-dimethyl-4-nitroso aniline (2), 4-dimethyl amino benzaldehyde (3), phthalaldehyde, (4) and tetramethyl benzoquinone (5) has been investigated in acetonitrile/water mixture in the presence of titanium dioxide and oxygen. An attempt has been made to identify the products formed during the photooxidation process through GC/MS analysis technique. The photolysis of 2,2-dinitro biphenyl (1) leads to the formation of 2-hydroxy-2'-nitro biphenyl (6), 2,2'-dihydroxy biphenyl (7) and 2-biphenyl amine (11); whereas, N,N'-dimethyl-4-nitroso aniline (2) gave rise to N,N'-dimethyl-4-nitro aniline (14) and N,N'-dimethyl-1,4-benzenediamine (15). However, the photolysis of 4-dimethyl amino benzaldehyde (3) yielded only a demethylated product (18). The illumination of phthalaldehyde (4), on the other hand, led to the formation of two products such as 1(3H)-isobenzofuranone (24) and 2-formyl-benzoic acid (21). Two intermediate products, tetramethyl hydroquinone (35) and 2,5-furandione3,4-dimethyl (34) have been identified in case of tetramethyl benzoquinone (5). The products have been identified by comparing the molecular ion and mass fragmentation peaks of the products with those reported in the GUMS library. A probable mechanism for the formation of the products has been proposed. (c) 2005 Elsevier B.V. All rights reserved.