Abstract Trifluromethyl substitution on the pyrazole ring was found to enhance photoreactivity via the P 4 pathway which involves interchange of the N2-C3 ring atoms. Thus, 1-methyl-3-(trifluromethyl) pyrazole (1) and 1-methyl-5-(trifluromethyl) pyrazole (3) transposed with a P 4/P 6 or P 4/P 6+ P 7 ratio of 2.1: 1. 1-methyl-4-(trifluromethyl) pyrazole (2) transposed regiospecifically by the P 4 transposition pathway. Compounds 2 and 3 ...