The reaction of the oxadiazapentane (CF 3) 2NON(CF 3) 2 ( 1) with the alkenes CH 2=CHX (X=Br, Cl, Ph, CN), CH 2=CX 2 (X=Cl, F), CHCl=CCl 2 and CF 2=CCl 2 at c. 20 °C gives in each case a single 1:1 adduct formed via initial (CF 3) 2N· radical attack. With the alkene CH 2=CHF, bidirectional radical attack occurs to afford the 1:1 adducts (CF 3) 2NCH 2CHFON(CF 3) 2 and (CF 3) 2NCHFCH 2ON(CF 3) 2 in the ratio 94:6, while with ( E)-CHCl=CHCl a mixture of the erythro and threo 1:1 adducts is formed (ratio 70:30). Reaction of 1 with the alkene CCl 2=CCl 2 at 50 °C gives the hydrazine (CF 3) 2NN(CF 3) 2 (39%), the 1:1 adduct (CF 3) 2NCCl 2CCl 2ON(CF 3) 2 (21%) and the 2:1 adduct of the oxyl (CF 3) 2NO· and the alkene, i.e. (CF 3) 2NOCCl 2CCl 2ON(CF 3) 2 (39%), while with cyclohexene allylic hydrogen abstraction competes with addition to afford the compounds (CF 3) 2NH (4%), (CF 3) 2NO CHCH=CH(CH 2) 2C H 2 (27%), (CF 3) 2N CH(CH 2) 4C H 2 (23%) and the 1:1 adduct (CF 3) 2N CH(CH 2) 4C HON(CF 3) 2 (44%). From competition experiments, the order of reactivity of alkenes, CH 2= CCl 2 〉 CHF= CF 2 〉 CH 2= CHCl 〉 CH 2= CH 2 〉 CH 2= CHF 〉 CH 2= CF 2 〉 CHCl = CCl 2 〉 CCl 2 〉 CCl 2 = CCl 2, towards (CF 3) 2N· radical attack is obtained.