Abstract Using similar procedures, the syntheses of [2-14 C]-malononitrile and malono [14 C] nitrile are described. Condensation with o-chlorobenzaldehyde affords [2-14 C]-o- chlorobenzylidenemalononitrile and o-chlorobenzylidenemalono [14 C] nitrile respectively. The syntheses of [3 H] o-chlorobenzaldehyde and o-chlorobenz [14 C] aldehyde, again by a common sequence of reactions, is described and with malononitrile gives [3 H]-o- ...